/* * linux/fs/namei.c * * Copyright (C) 1991, 1992 Linus Torvalds */ /* * Some corrections by tytso. */ /* [Feb 1997 T. Schoebel-Theuer] Complete rewrite of the pathname * lookup logic. */ /* [Feb-Apr 2000, AV] Rewrite to the new namespace architecture. */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include "internal.h" #include "mount.h" /* [Feb-1997 T. Schoebel-Theuer] * Fundamental changes in the pathname lookup mechanisms (namei) * were necessary because of omirr. The reason is that omirr needs * to know the _real_ pathname, not the user-supplied one, in case * of symlinks (and also when transname replacements occur). * * The new code replaces the old recursive symlink resolution with * an iterative one (in case of non-nested symlink chains). It does * this with calls to _follow_link(). * As a side effect, dir_namei(), _namei() and follow_link() are now * replaced with a single function lookup_dentry() that can handle all * the special cases of the former code. * * With the new dcache, the pathname is stored at each inode, at least as * long as the refcount of the inode is positive. As a side effect, the * size of the dcache depends on the inode cache and thus is dynamic. * * [29-Apr-1998 C. Scott Ananian] Updated above description of symlink * resolution to correspond with current state of the code. * * Note that the symlink resolution is not *completely* iterative. * There is still a significant amount of tail- and mid- recursion in * the algorithm. Also, note that _readlink() is not used in * lookup_dentry(): lookup_dentry() on the result of _readlink() * may return different results than _follow_link(). Many virtual * filesystems (including /proc) exhibit this behavior. */ /* [24-Feb-97 T. Schoebel-Theuer] Side effects caused by new implementation: * New symlink semantics: when open() is called with flags O_CREAT | O_EXCL * and the name already exists in form of a symlink, try to create the new * name indicated by the symlink. The old code always complained that the * name already exists, due to not following the symlink even if its target * is nonexistent. The new semantics affects also mknod() and link() when * the name is a symlink pointing to a non-existent name. * * I don't know which semantics is the right one, since I have no access * to standards. But I found by trial that HP-UX 9.0 has the full "new" * semantics implemented, while SunOS 4.1.1 and Solaris (SunOS 5.4) have the * "old" one. Personally, I think the new semantics is much more logical. * Note that "ln old new" where "new" is a symlink pointing to a non-existing * file does succeed in both HP-UX and SunOs, but not in Solaris * and in the old Linux semantics. */ /* [16-Dec-97 Kevin Buhr] For security reasons, we change some symlink * semantics. See the comments in "open_namei" and "do_link" below. * * [10-Sep-98 Alan Modra] Another symlink change. */ /* [Feb-Apr 2000 AV] Complete rewrite. Rules for symlinks: * inside the path - always follow. * in the last component in creation/removal/renaming - never follow. * if LOOKUP_FOLLOW passed - follow. * if the pathname has trailing slashes - follow. * otherwise - don't follow. * (applied in that order). * * [Jun 2000 AV] Inconsistent behaviour of open() in case if flags==O_CREAT * restored for 2.4. This is the last surviving part of old 4.2BSD bug. * During the 2.4 we need to fix the userland stuff depending on it - * hopefully we will be able to get rid of that wart in 2.5. So far only * XEmacs seems to be relying on it... */ /* * [Sep 2001 AV] Single-semaphore locking scheme (kudos to David Holland) * implemented. Let's see if raised priority of ->s_vfs_rename_mutex gives * any extra contention... */ /* In order to reduce some races, while at the same time doing additional * checking and hopefully speeding things up, we copy filenames to the * kernel data space before using them.. * * POSIX.1 2.4: an empty pathname is invalid (ENOENT). * PATH_MAX includes the nul terminator --RR. */ void final_putname(struct filename *name) { if (name->separate) { __putname(name->name); kfree(name); } else { __putname(name); } } #define EMBEDDED_NAME_MAX (PATH_MAX - sizeof(struct filename)) static struct filename * getname_flags(const char __user *filename, int flags, int *empty) { struct filename *result, *err; int len; long max; char *kname; result = audit_reusename(filename); if (result) return result; result = __getname(); if (unlikely(!result)) return ERR_PTR(-ENOMEM); /* * First, try to embed the struct filename inside the names_cache * allocation */ kname = (char *)result + sizeof(*result); result->name = kname; result->separate = false; max = EMBEDDED_NAME_MAX; recopy: len = strncpy_from_user(kname, filename, max); if (unlikely(len < 0)) { err = ERR_PTR(len); goto error; } /* * Uh-oh. We have a name that's approaching PATH_MAX. Allocate a * separate struct filename so we can dedicate the entire * names_cache allocation for the pathname, and re-do the copy from * userland. */ if (len == EMBEDDED_NAME_MAX && max == EMBEDDED_NAME_MAX) { kname = (char *)result; result = kzalloc(sizeof(*result), GFP_KERNEL); if (!result) { err = ERR_PTR(-ENOMEM); result = (struct filename *)kname; goto error; } result->name = kname; result->separate = true; max = PATH_MAX; goto recopy; } /* The empty path is special. */ if (unlikely(!len)) { if (empty) *empty = 1; err = ERR_PTR(-ENOENT); if (!(flags & LOOKUP_EMPTY)) goto error; } err = ERR_PTR(-ENAMETOOLONG); if (unlikely(len >= PATH_MAX)) goto error; result->uptr = filename; result->aname = NULL; audit_getname(result); return result; error: final_putname(result); return err; } struct filename * getname(const char __user * filename) { return getname_flags(filename, 0, NULL); } /* * The "getname_kernel()" interface doesn't do pathnames longer * than EMBEDDED_NAME_MAX. Deal with it - you're a kernel user. */ struct filename * getname_kernel(const char * filename) { struct filename *result; char *kname; int len; len = strlen(filename); if (len >= EMBEDDED_NAME_MAX) return ERR_PTR(-ENAMETOOLONG); result = __getname(); if (unlikely(!result)) return ERR_PTR(-ENOMEM); kname = (char *)result + sizeof(*result); result->name = kname; result->uptr = NULL; result->aname = NULL; result->separate = false; strlcpy(kname, filename, EMBEDDED_NAME_MAX); return result; } #ifdef CONFIG_AUDITSYSCALL void putname(struct filename *name) { if (unlikely(!audit_dummy_context())) return audit_putname(name); final_putname(name); } #endif static int check_acl(struct inode *inode, int mask) { #ifdef CONFIG_FS_POSIX_ACL struct posix_acl *acl; if (mask & MAY_NOT_BLOCK) { acl = get_cached_acl_rcu(inode, ACL_TYPE_ACCESS); if (!acl) return -EAGAIN; /* no ->get_acl() calls in RCU mode... */ if (acl == ACL_NOT_CACHED) return -ECHILD; return posix_acl_permission(inode, acl, mask & ~MAY_NOT_BLOCK); } acl = get_acl(inode, ACL_TYPE_ACCESS); if (IS_ERR(acl)) return PTR_ERR(acl); if (acl) { int error = posix_acl_permission(inode, acl, mask); posix_acl_release(acl); return error; } #endif return -EAGAIN; } /* * This does the basic permission checking */ static int acl_permission_check(struct inode *inode, int mask) { unsigned int mode = inode->i_mode; if (likely(uid_eq(current_fsuid(), inode->i_uid))) mode >>= 6; else { if (IS_POSIXACL(inode) && (mode & S_IRWXG)) { int error = check_acl(inode, mask); if (error != -EAGAIN) return error; } if (in_group_p(inode->i_gid)) mode >>= 3; } /* * If the DACs are ok we don't need any capability check. */ if ((mask & ~mode & (MAY_READ | MAY_WRITE | MAY_EXEC)) == 0) return 0; return -EACCES; } /** * generic_permission - check for access rights on a Posix-like filesystem * @inode: inode to check access rights for * @mask: right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC, ...) * * Used to check for read/write/execute permissions on a file. * We use "fsuid" for this, letting us set arbitrary permissions * for filesystem access without changing the "normal" uids which * are used for other things. * * generic_permission is rcu-walk aware. It returns -ECHILD in case an rcu-walk * request cannot be satisfied (eg. requires blocking or too much complexity). * It would then be called again in ref-walk mode. */ int generic_permission(struct inode *inode, int mask) { int ret; /* * Do the basic permission checks. */ ret = acl_permission_check(inode, mask); if (ret != -EACCES) return ret; if (S_ISDIR(inode->i_mode)) { /* DACs are overridable for directories */ if (capable_wrt_inode_uidgid(inode, CAP_DAC_OVERRIDE)) return 0; if (!(mask & MAY_WRITE)) if (capable_wrt_inode_uidgid(inode, CAP_DAC_READ_SEARCH)) return 0; return -EACCES; } /* * Read/write DACs are always overridable. * Executable DACs are overridable when there is * at least one exec bit set. */ if (!(mask & MAY_EXEC) || (inode->i_mode & S_IXUGO)) if (capable_wrt_inode_uidgid(inode, CAP_DAC_OVERRIDE)) return 0; /* * Searching includes executable on directories, else just read. */ mask &= MAY_READ | MAY_WRITE | MAY_EXEC; if (mask == MAY_READ) if (capable_wrt_inode_uidgid(inode, CAP_DAC_READ_SEARCH)) return 0; return -EACCES; } EXPORT_SYMBOL(generic_permission); /* * We _really_ want to just do "generic_permission()" without * even looking at the inode->i_op values. So we keep a cache * flag in inode->i_opflags, that says "this has not special * permission function, use the fast case". */ static inline int do_inode_permission(struct inode *inode, int mask) { if (unlikely(!(inode->i_opflags & IOP_FASTPERM))) { if (likely(inode->i_op->permission)) return inode->i_op->permission(inode, mask); /* This gets set once for the inode lifetime */ spin_lock(&inode->i_lock); inode->i_opflags |= IOP_FASTPERM; spin_unlock(&inode->i_lock); } return generic_permission(inode, mask); } /** * __inode_permission - Check for access rights to a given inode * @inode: Inode to check permission on * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC) * * Check for read/write/execute permissions on an inode. * * When checking for MAY_APPEND, MAY_WRITE must also be set in @mask. * * This does not check for a read-only file system. You probably want * inode_permission(). */ int __inode_permission(struct inode *inode, int mask) { int retval; if (unlikely(mask & MAY_WRITE)) { /* * Nobody gets write access to an immutable file. */ if (IS_IMMUTABLE(inode)) return -EACCES; } retval = do_inode_permission(inode, mask); if (retval) return retval; retval = devcgroup_inode_permission(inode, mask); if (retval) return retval; return security_inode_permission(inode, mask); } EXPORT_SYMBOL(__inode_permission); /** * sb_permission - Check superblock-level permissions * @sb: Superblock of inode to check permission on * @inode: Inode to check permission on * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC) * * Separate out file-system wide checks from inode-specific permission checks. */ static int sb_permission(struct super_block *sb, struct inode *inode, int mask) { if (unlikely(mask & MAY_WRITE)) { umode_t mode = inode->i_mode; /* Nobody gets write access to a read-only fs. */ if ((sb->s_flags & MS_RDONLY) && (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode))) return -EROFS; } return 0; } /** * inode_permission - Check for access rights to a given inode * @inode: Inode to check permission on * @mask: Right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC) * * Check for read/write/execute permissions on an inode. We use fs[ug]id for * this, letting us set arbitrary permissions for filesystem access without * changing the "normal" UIDs which are used for other things. * * When checking for MAY_APPEND, MAY_WRITE must also be set in @mask. */ int inode_permission(struct inode *inode, int mask) { int retval; retval = sb_permission(inode->i_sb, inode, mask); if (retval) return retval; return __inode_permission(inode, mask); } EXPORT_SYMBOL(inode_permission); /** * path_get - get a reference to a path * @path: path to get the reference to * * Given a path increment the reference count to the dentry and the vfsmount. */ void path_get(const struct path *path) { mntget(path->mnt); dget(path->dentry); } EXPORT_SYMBOL(path_get); /** * path_put - put a reference to a path * @path: path to put the reference to * * Given a path decrement the reference count to the dentry and the vfsmount. */ void path_put(const struct path *path) { dput(path->dentry); mntput(path->mnt); } EXPORT_SYMBOL(path_put); struct nameidata { struct path path; struct qstr last; struct path root; struct inode *inode; /* path.dentry.d_inode */ unsigned int flags; unsigned seq, m_seq; int last_type; unsigned depth; struct file *base; char *saved_names[MAX_NESTED_LINKS + 1]; }; /* * Path walking has 2 modes, rcu-walk and ref-walk (see * Documentation/filesystems/path-lookup.txt). In situations when we can't * continue in RCU mode, we attempt to drop out of rcu-walk mode and grab * normal reference counts on dentries and vfsmounts to transition to rcu-walk * mode. Refcounts are grabbed at the last known good point before rcu-walk * got stuck, so ref-walk may continue from there. If this is not successful * (eg. a seqcount has changed), then failure is returned and it's up to caller * to restart the path walk from the beginning in ref-walk mode. */ /** * unlazy_walk - try to switch to ref-walk mode. * @nd: nameidata pathwalk data * @dentry: child of nd->path.dentry or NULL * Returns: 0 on success, -ECHILD on failure * * unlazy_walk attempts to legitimize the current nd->path, nd->root and dentry * for ref-walk mode. @dentry must be a path found by a do_lookup call on * @nd or NULL. Must be called from rcu-walk context. */ static int unlazy_walk(struct nameidata *nd, struct dentry *dentry) { struct fs_struct *fs = current->fs; struct dentry *parent = nd->path.dentry; BUG_ON(!(nd->flags & LOOKUP_RCU)); /* * After legitimizing the bastards, terminate_walk() * will do the right thing for non-RCU mode, and all our * subsequent exit cases should rcu_read_unlock() * before returning. Do vfsmount first; if dentry * can't be legitimized, just set nd->path.dentry to NULL * and rely on dput(NULL) being a no-op. */ if (!legitimize_mnt(nd->path.mnt, nd->m_seq)) return -ECHILD; nd->flags &= ~LOOKUP_RCU; if (!lockref_get_not_dead(&parent->d_lockref)) { nd->path.dentry = NULL; goto out; } /* * For a negative lookup, the lookup sequence point is the parents * sequence point, and it only needs to revalidate the parent dentry. * * For a positive lookup, we need to move both the parent and the * dentry from the RCU domain to be properly refcounted. And the * sequence number in the dentry validates *both* dentry counters, * since we checked the sequence number of the parent after we got * the child sequence number. So we know the parent must still * be valid if the child sequence number is still valid. */ if (!dentry) { if (read_seqcount_retry(&parent->d_seq, nd->seq)) goto out; BUG_ON(nd->inode != parent->d_inode); } else { if (!lockref_get_not_dead(&dentry->d_lockref)) goto out; if (read_seqcount_retry(&dentry->d_seq, nd->seq)) goto drop_dentry; } /* * Sequence counts matched. Now make sure that the root is * still valid and get it if required. */ if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) { spin_lock(&fs->lock); if (nd->root.mnt != fs->root.mnt || nd->root.dentry != fs->root.dentry) goto unlock_and_drop_dentry; path_get(&nd->root); spin_unlock(&fs->lock); } rcu_read_unlock(); return 0; unlock_and_drop_dentry: spin_unlock(&fs->lock); drop_dentry: rcu_read_unlock(); dput(dentry); goto drop_root_mnt; out: rcu_read_unlock(); drop_root_mnt: if (!(nd->flags & LOOKUP_ROOT)) nd->root.mnt = NULL; return -ECHILD; } static inline int d_revalidate(struct dentry *dentry, unsigned int flags) { return dentry->d_op->d_revalidate(dentry, flags); } /** * complete_walk - successful completion of path walk * @nd: pointer nameidata * * If we had been in RCU mode, drop out of it and legitimize nd->path. * Revalidate the final result, unless we'd already done that during * the path walk or the filesystem doesn't ask for it. Return 0 on * success, -error on failure. In case of failure caller does not * need to drop nd->path. */ static int complete_walk(struct nameidata *nd) { struct dentry *dentry = nd->path.dentry; int status; if (nd->flags & LOOKUP_RCU) { nd->flags &= ~LOOKUP_RCU; if (!(nd->flags & LOOKUP_ROOT)) nd->root.mnt = NULL; if (!legitimize_mnt(nd->path.mnt, nd->m_seq)) { rcu_read_unlock(); return -ECHILD; } if (unlikely(!lockref_get_not_dead(&dentry->d_lockref))) { rcu_read_unlock(); mntput(nd->path.mnt); return -ECHILD; } if (read_seqcount_retry(&dentry->d_seq, nd->seq)) { rcu_read_unlock(); dput(dentry); mntput(nd->path.mnt); return -ECHILD; } rcu_read_unlock(); } if (likely(!(nd->flags & LOOKUP_JUMPED))) return 0; if (likely(!(dentry->d_flags & DCACHE_OP_WEAK_REVALIDATE))) return 0; status = dentry->d_op->d_weak_revalidate(dentry, nd->flags); if (status > 0) return 0; if (!status) status = -ESTALE; path_put(&nd->path); return status; } static __always_inline void set_root(struct nameidata *nd) { get_fs_root(current->fs, &nd->root); } static int link_path_walk(const char *, struct nameidata *); static __always_inline unsigned set_root_rcu(struct nameidata *nd) { struct fs_struct *fs = current->fs; unsigned seq, res; do { seq = read_seqcount_begin(&fs->seq); nd->root = fs->root; res = __read_seqcount_begin(&nd->root.dentry->d_seq); } while (read_seqcount_retry(&fs->seq, seq)); return res; } static void path_put_conditional(struct path *path, struct nameidata *nd) { dput(path->dentry); if (path->mnt != nd->path.mnt) mntput(path->mnt); } static inline void path_to_nameidata(const struct path *path, struct nameidata *nd) { if (!(nd->flags & LOOKUP_RCU)) { dput(nd->path.dentry); if (nd->path.mnt != path->mnt) mntput(nd->path.mnt); } nd->path.mnt = path->mnt; nd->path.dentry = path->dentry; } /* * Helper to directly jump to a known parsed path from ->follow_link, * caller must have taken a reference to path beforehand. */ void nd_jump_link(struct nameidata *nd, struct path *path) { path_put(&nd->path); nd->path = *path; nd->inode = nd->path.dentry->d_inode; nd->flags |= LOOKUP_JUMPED; } void nd_set_link(struct nameidata *nd, char *path) { nd->saved_names[nd->depth] = path; } EXPORT_SYMBOL(nd_set_link); char *nd_get_link(struct nameidata *nd) { return nd->saved_names[nd->depth]; } EXPORT_SYMBOL(nd_get_link); static inline void put_link(struct nameidata *nd, struct path *link, void *cookie) { struct inode *inode = link->dentry->d_inode; if (inode->i_op->put_link) inode->i_op->put_link(link->dentry, nd, cookie); path_put(link); } int sysctl_protected_symlinks __read_mostly = 0; int sysctl_protected_hardlinks __read_mostly = 0; /** * may_follow_link - Check symlink following for unsafe situations * @link: The path of the symlink * @nd: nameidata pathwalk data * * In the case of the sysctl_protected_symlinks sysctl being enabled, * CAP_DAC_OVERRIDE needs to be specifically ignored if the symlink is * in a sticky world-writable directory. This is to protect privileged * processes from failing races against path names that may change out * from under them by way of other users creating malicious symlinks. * It will permit symlinks to be followed only when outside a sticky * world-writable directory, or when the uid of the symlink and follower * match, or when the directory owner matches the symlink's owner. * * Returns 0 if following the symlink is allowed, -ve on error. */ static inline int may_follow_link(struct path *link, struct nameidata *nd) { const struct inode *inode; const struct inode *parent; if (!sysctl_protected_symlinks) return 0; /* Allowed if owner and follower match. */ inode = link->dentry->d_inode; if (uid_eq(current_cred()->fsuid, inode->i_uid)) return 0; /* Allowed if parent directory not sticky and world-writable. */ parent = nd->path.dentry->d_inode; if ((parent->i_mode & (S_ISVTX|S_IWOTH)) != (S_ISVTX|S_IWOTH)) return 0; /* Allowed if parent directory and link owner match. */ if (uid_eq(parent->i_uid, inode->i_uid)) return 0; audit_log_link_denied("follow_link", link); path_put_conditional(link, nd); path_put(&nd->path); return -EACCES; } /** * safe_hardlink_source - Check for safe hardlink conditions * @inode: the source inode to hardlink from * * Return false if at least one of the following conditions: * - inode is not a regular file * - inode is setuid * - inode is setgid and group-exec * - access failure for read and write * * Otherwise returns true. */ static bool safe_hardlink_source(struct inode *inode) { umode_t mode = inode->i_mode; /* Special files should not get pinned to the filesystem. */ if (!S_ISREG(mode)) return false; /* Setuid files should not get pinned to the filesystem. */ if (mode & S_ISUID) return false; /* Executable setgid files should not get pinned to the filesystem. */ if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) return false; /* Hardlinking to unreadable or unwritable sources is dangerous. */ if (inode_permission(inode, MAY_READ | MAY_WRITE)) return false; return true; } /** * may_linkat - Check permissions for creating a hardlink * @link: the source to hardlink from * * Block hardlink when all of: * - sysctl_protected_hardlinks enabled * - fsuid does not match inode * - hardlink source is unsafe (see safe_hardlink_source() above) * - not CAP_FOWNER * * Returns 0 if successful, -ve on error. */ static int may_linkat(struct path *link) { const struct cred *cred; struct inode *inode; if (!sysctl_protected_hardlinks) return 0; cred = current_cred(); inode = link->dentry->d_inode; /* Source inode owner (or CAP_FOWNER) can hardlink all they like, * otherwise, it must be a safe source. */ if (uid_eq(cred->fsuid, inode->i_uid) || safe_hardlink_source(inode) || capable(CAP_FOWNER)) return 0; audit_log_link_denied("linkat", link); return -EPERM; } static __always_inline int follow_link(struct path *link, struct nameidata *nd, void **p) { struct dentry *dentry = link->dentry; int error; char *s; BUG_ON(nd->flags & LOOKUP_RCU); if (link->mnt == nd->path.mnt) mntget(link->mnt); error = -ELOOP; if (unlikely(current->total_link_count >= 40)) goto out_put_nd_path; cond_resched(); current->total_link_count++; touch_atime(link); nd_set_link(nd, NULL); error = security_inode_follow_link(link->dentry, nd); if (error) goto out_put_nd_path; nd->last_type = LAST_BIND; *p = dentry->d_inode->i_op->follow_link(dentry, nd); error = PTR_ERR(*p); if (IS_ERR(*p)) goto out_put_nd_path; error = 0; s = nd_get_link(nd); if (s) { if (unlikely(IS_ERR(s))) { path_put(&nd->path); put_link(nd, link, *p); return PTR_ERR(s); } if (*s == '/') { if (!nd->root.mnt) set_root(nd); path_put(&nd->path); nd->path = nd->root; path_get(&nd->root); nd->flags |= LOOKUP_JUMPED; } nd->inode = nd->path.dentry->d_inode; error = link_path_walk(s, nd); if (unlikely(error)) put_link(nd, link, *p); } return error; out_put_nd_path: *p = NULL; path_put(&nd->path); path_put(link); return error; } static int follow_up_rcu(struct path *path) { struct mount *mnt = real_mount(path->mnt); struct mount *parent; struct dentry *mountpoint; parent = mnt->mnt_parent; if (&parent->mnt == path->mnt) return 0; mountpoint = mnt->mnt_mountpoint; path->dentry = mountpoint; path->mnt = &parent->mnt; return 1; } /* * follow_up - Find the mountpoint of path's vfsmount * * Given a path, find the mountpoint of its source file system. * Replace @path with the path of the mountpoint in the parent mount. * Up is towards /. * * Return 1 if we went up a level and 0 if we were already at the * root. */ int follow_up(struct path *path) { struct mount *mnt = real_mount(path->mnt); struct mount *parent; struct dentry *mountpoint; read_seqlock_excl(&mount_lock); parent = mnt->mnt_parent; if (parent == mnt) { read_sequnlock_excl(&mount_lock); return 0; } mntget(&parent->mnt); mountpoint = dget(mnt->mnt_mountpoint); read_sequnlock_excl(&mount_lock); dput(path->dentry); path->dentry = mountpoint; mntput(path->mnt); path->mnt = &parent->mnt; return 1; } EXPORT_SYMBOL(follow_up); /* * Perform an automount * - return -EISDIR to tell follow_managed() to stop and return the path we * were called with. */ static int follow_automount(struct path *path, unsigned flags, bool *need_mntput) { struct vfsmount *mnt; int err; if (!path->dentry->d_op || !path->dentry->d_op->d_automount) return -EREMOTE; /* We don't want to mount if someone's just doing a stat - * unless they're stat'ing a directory and appended a '/' to * the name. * * We do, however, want to mount if someone wants to open or * create a file of any type under the mountpoint, wants to * traverse through the mountpoint or wants to open the * mounted directory. Also, autofs may mark negative dentries * as being automount points. These will need the attentions * of the daemon to instantiate them before they can be used. */ if (!(flags & (LOOKUP_PARENT | LOOKUP_DIRECTORY | LOOKUP_OPEN | LOOKUP_CREATE | LOOKUP_AUTOMOUNT)) && path->dentry->d_inode) return -EISDIR; current->total_link_count++; if (current->total_link_count >= 40) return -ELOOP; mnt = path->dentry->d_op->d_automount(path); if (IS_ERR(mnt)) { /* * The filesystem is allowed to return -EISDIR here to indicate * it doesn't want to automount. For instance, autofs would do * this so that its userspace daemon can mount on this dentry. * * However, we can only permit this if it's a terminal point in * the path being looked up; if it wasn't then the remainder of * the path is inaccessible and we should say so. */ if (PTR_ERR(mnt) == -EISDIR && (flags & LOOKUP_PARENT)) return -EREMOTE; return PTR_ERR(mnt); } if (!mnt) /* mount collision */ return 0; if (!*need_mntput) { /* lock_mount() may release path->mnt on error */ mntget(path->mnt); *need_mntput = true; } err = finish_automount(mnt, path); switch (err) { case -EBUSY: /* Someone else made a mount here whilst we were busy */ return 0; case 0: path_put(path); path->mnt = mnt; path->dentry = dget(mnt->mnt_root); return 0; default: return err; } } /* * Handle a dentry that is managed in some way. * - Flagged for transit management (autofs) * - Flagged as mountpoint * - Flagged as automount point * * This may only be called in refwalk mode. * * Serialization is taken care of in namespace.c */ static int follow_managed(struct path *path, unsigned flags) { struct vfsmount *mnt = path->mnt; /* held by caller, must be left alone */ unsigned managed; bool need_mntput = false; int ret = 0; /* Given that we're not holding a lock here, we retain the value in a * local variable for each dentry as we look at it so that we don't see * the components of that value change under us */ while (managed = ACCESS_ONCE(path->dentry->d_flags), managed &= DCACHE_MANAGED_DENTRY, unlikely(managed != 0)) { /* Allow the filesystem to manage the transit without i_mutex * being held. */ if (managed & DCACHE_MANAGE_TRANSIT) { BUG_ON(!path->dentry->d_op); BUG_ON(!path->dentry->d_op->d_manage); ret = path->dentry->d_op->d_manage(path->dentry, false); if (ret < 0) break; } /* Transit to a mounted filesystem. */ if (managed & DCACHE_MOUNTED) { struct vfsmount *mounted = lookup_mnt(path); if (mounted) { dput(path->dentry); if (need_mntput) mntput(path->mnt); path->mnt = mounted; path->dentry = dget(mounted->mnt_root); need_mntput = true; continue; } /* Something is mounted on this dentry in another * namespace and/or whatever was mounted there in this * namespace got unmounted before lookup_mnt() could * get it */ } /* Handle an automount point */ if (managed & DCACHE_NEED_AUTOMOUNT) { ret = follow_automount(path, flags, &need_mntput); if (ret < 0) break; continue; } /* We didn't change the current path point */ break; } if (need_mntput && path->mnt == mnt) mntput(path->mnt); if (ret == -EISDIR) ret = 0; return ret < 0 ? ret : need_mntput; } int follow_down_one(struct path *path) { struct vfsmount *mounted; mounted = lookup_mnt(path); if (mounted) { dput(path->dentry); mntput(path->mnt); path->mnt = mounted; path->dentry = dget(mounted->mnt_root); return 1; } return 0; } EXPORT_SYMBOL(follow_down_one); static inline int managed_dentry_rcu(struct dentry *dentry) { return (dentry->d_flags & DCACHE_MANAGE_TRANSIT) ? dentry->d_op->d_manage(dentry, true) : 0; } /* * Try to skip to top of mountpoint pile in rcuwalk mode. Fail if * we meet a managed dentry that would need blocking. */ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path, struct inode **inode) { for (;;) { struct mount *mounted; /* * Don't forget we might have a non-mountpoint managed dentry * that wants to block transit. */ switch (managed_dentry_rcu(path->dentry)) { case -ECHILD: default: return false; case -EISDIR: return true; case 0: break; } if (!d_mountpoint(path->dentry)) return !(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT); mounted = __lookup_mnt(path->mnt, path->dentry); if (!mounted) break; path->mnt = &mounted->mnt; path->dentry = mounted->mnt.mnt_root; nd->flags |= LOOKUP_JUMPED; nd->seq = read_seqcount_begin(&path->dentry->d_seq); /* * Update the inode too. We don't need to re-check the * dentry sequence number here after this d_inode read, * because a mount-point is always pinned. */ *inode = path->dentry->d_inode; } return !read_seqretry(&mount_lock, nd->m_seq) && !(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT); } static int follow_dotdot_rcu(struct nameidata *nd) { struct inode *inode = nd->inode; if (!nd->root.mnt) set_root_rcu(nd); while (1) { if (nd->path.dentry == nd->root.dentry && nd->path.mnt == nd->root.mnt) { break; } if (nd->path.dentry != nd->path.mnt->mnt_root) { struct dentry *old = nd->path.dentry; struct dentry *parent = old->d_parent; unsigned seq; inode = parent->d_inode; seq = read_seqcount_begin(&parent->d_seq); if (read_seqcount_retry(&old->d_seq, nd->seq)) goto failed; nd->path.dentry = parent; nd->seq = seq; break; } if (!follow_up_rcu(&nd->path)) break; inode = nd->path.dentry->d_inode; nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq); } while (d_mountpoint(nd->path.dentry)) { struct mount *mounted; mounted = __lookup_mnt(nd->path.mnt, nd->path.dentry); if (!mounted) break; nd->path.mnt = &mounted->mnt; nd->path.dentry = mounted->mnt.mnt_root; inode = nd->path.dentry->d_inode; nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq); if (read_seqretry(&mount_lock, nd->m_seq)) goto failed; } nd->inode = inode; return 0; failed: nd->flags &= ~LOOKUP_RCU; if (!(nd->flags & LOOKUP_ROOT)) nd->root.mnt = NULL; rcu_read_unlock(); return -ECHILD; } /* * Follow down to the covering mount currently visible to userspace. At each * point, the filesystem owning that dentry may be queried as to whether the * caller is permitted to proceed or not. */ int follow_down(struct path *path) { unsigned managed; int ret; while (managed = ACCESS_ONCE(path->dentry->d_flags), unlikely(managed & DCACHE_MANAGED_DENTRY)) { /* Allow the filesystem to manage the transit without i_mutex * being held. * * We indicate to the filesystem if someone is trying to mount * something here. This gives autofs the chance to deny anyone * other than its daemon the right to mount on its * superstructure. * * The filesystem may sleep at this point. */ if (managed & DCACHE_MANAGE_TRANSIT) { BUG_ON(!path->dentry->d_op); BUG_ON(!path->dentry->d_op->d_manage); ret = path->dentry->d_op->d_manage( path->dentry, false); if (ret < 0) return ret == -EISDIR ? 0 : ret; } /* Transit to a mounted filesystem. */ if (managed & DCACHE_MOUNTED) { struct vfsmount *mounted = lookup_mnt(path); if (!mounted) break; dput(path->dentry); mntput(path->mnt); path->mnt = mounted; path->dentry = dget(mounted->mnt_root); continue; } /* Don't handle automount points here */ break; } return 0; } EXPORT_SYMBOL(follow_down); /* * Skip to top of mountpoint pile in refwalk mode for follow_dotdot() */ static void follow_mount(struct path *path) { while (d_mountpoint(path->dentry)) { struct vfsmount *mounted = lookup_mnt(path); if (!mounted) break; dput(path->dentry); mntput(path->mnt); path->mnt = mounted; path->dentry = dget(mounted->mnt_root); } } static void follow_dotdot(struct nameidata *nd) { if (!nd->root.mnt) set_root(nd); while(1) { struct dentry *old = nd->path.dentry; if (nd->path.dentry == nd->root.dentry && nd->path.mnt == nd->root.mnt) { break; } if (nd->path.dentry != nd->path.mnt->mnt_root) { /* rare case of legitimate dget_parent()... */ nd->path.dentry = dget_parent(nd->path.dentry); dput(old); break; } if (!follow_up(&nd->path)) break; } follow_mount(&nd->path); nd->inode = nd->path.dentry->d_inode; } /* * This looks up the name in dcache, possibly revalidates the old dentry and * allocates a new one if not found or not valid. In the need_lookup argument * returns whether i_op->lookup is necessary. * * dir->d_inode->i_mutex must be held */ static struct dentry *lookup_dcache(struct qstr *name, struct dentry *dir, unsigned int flags, bool *need_lookup) { struct dentry *dentry; int error; *need_lookup = false; dentry = d_lookup(dir, name); if (dentry) { if (dentry->d_flags & DCACHE_OP_REVALIDATE) { error = d_revalidate(dentry, flags); if (unlikely(error <= 0)) { if (error < 0) { dput(dentry); return ERR_PTR(error); } else { d_invalidate(dentry); dput(dentry); dentry = NULL; } } } } if (!dentry) { dentry = d_alloc(dir, name); if (unlikely(!dentry)) return ERR_PTR(-ENOMEM); *need_lookup = true; } return dentry; } /* * Call i_op->lookup on the dentry. The dentry must be negative and * unhashed. * * dir->d_inode->i_mutex must be held */ static struct dentry *lookup_real(struct inode *dir, struct dentry *dentry, unsigned int flags) { struct dentry *old; /* Don't create child dentry for a dead directory. */ if (unlikely(IS_DEADDIR(dir))) { dput(dentry); return ERR_PTR(-ENOENT); } old = dir->i_op->lookup(dir, dentry, flags); if (unlikely(old)) { dput(dentry); dentry = old; } return dentry; } static struct dentry *__lookup_hash(struct qstr *name, struct dentry *base, unsigned int flags) { bool need_lookup; struct dentry *dentry; dentry = lookup_dcache(name, base, flags, &need_lookup); if (!need_lookup) return dentry; return lookup_real(base->d_inode, dentry, flags); } /* * It's more convoluted than I'd like it to be, but... it's still fairly * small and for now I'd prefer to have fast path as straight as possible. * It _is_ time-critical. */ static int lookup_fast(struct nameidata *nd, struct path *path, struct inode **inode) { struct vfsmount *mnt = nd->path.mnt; struct dentry *dentry, *parent = nd->path.dentry; int need_reval = 1; int status = 1; int err; /* * Rename seqlock is not required here because in the off chance * of a false negative due to a concurrent rename, we're going to * do the non-racy lookup, below. */ if (nd->flags & LOOKUP_RCU) { unsigned seq; dentry = __d_lookup_rcu(parent, &nd->last, &seq); if (!dentry) goto unlazy; /* * This sequence count validates that the inode matches * the dentry name information from lookup. */ *inode = dentry->d_inode; if (read_seqcount_retry(&dentry->d_seq, seq)) return -ECHILD; /* * This sequence count validates that the parent had no * changes while we did the lookup of the dentry above. * * The memory barrier in read_seqcount_begin of child is * enough, we can use __read_seqcount_retry here. */ if (__read_seqcount_retry(&parent->d_seq, nd->seq)) return -ECHILD; nd->seq = seq; if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE)) { status = d_revalidate(dentry, nd->flags); if (unlikely(status <= 0)) { if (status != -ECHILD) need_reval = 0; goto unlazy; } } path->mnt = mnt; path->dentry = dentry; if (likely(__follow_mount_rcu(nd, path, inode))) return 0; unlazy: if (unlazy_walk(nd, dentry)) return -ECHILD; } else { dentry = __d_lookup(parent, &nd->last); } if (unlikely(!dentry)) goto need_lookup; if (unlikely(dentry->d_flags & DCACHE_OP_REVALIDATE) && need_reval) status = d_revalidate(dentry, nd->flags); if (unlikely(status <= 0)) { if (status < 0) { dput(dentry); return status; } d_invalidate(dentry); dput(dentry); goto need_lookup; } path->mnt = mnt; path->dentry = dentry; err = follow_managed(path, nd->flags); if (unlikely(err < 0)) { path_put_conditional(path, nd); return err; } if (err) nd->flags |= LOOKUP_JUMPED; *inode = path->dentry->d_inode; return 0; need_lookup: return 1; } /* Fast lookup failed, do it the slow way */ static int lookup_slow(struct nameidata *nd, struct path *path) { struct dentry *dentry, *parent; int err; parent = nd->path.dentry; BUG_ON(nd->inode != parent->d_inode); mutex_lock(&parent->d_inode->i_mutex); dentry = __lookup_hash(&nd->last, parent, nd->flags); mutex_unlock(&parent->d_inode->i_mutex); if (IS_ERR(dentry)) return PTR_ERR(dentry); path->mnt = nd->path.mnt; path->dentry = dentry; err = follow_managed(path, nd->flags); if (unlikely(err < 0)) { path_put_conditional(path, nd); return err; } if (err) nd->flags |= LOOKUP_JUMPED; return 0; } static inline int may_lookup(struct nameidata *nd) { if (nd->flags & LOOKUP_RCU) { int err = inode_permission(nd->inode, MAY_EXEC|MAY_NOT_BLOCK); if (err != -ECHILD) return err; if (unlazy_walk(nd, NULL)) return -ECHILD; } return inode_permission(nd->inode, MAY_EXEC); } static inline int handle_dots(struct nameidata *nd, int type) { if (type == LAST_DOTDOT) { if (nd->flags & LOOKUP_RCU) { if (follow_dotdot_rcu(nd)) return -ECHILD; } else follow_dotdot(nd); } return 0; } static void terminate_walk(struct nameidata *nd) { if (!(nd->flags & LOOKUP_RCU)) { path_put(&nd->path); } else { nd->flags &= ~LOOKUP_RCU; if (!(nd->flags & LOOKUP_ROOT)) nd->root.mnt = NULL; rcu_read_unlock(); } } /* * Do we need to follow links? We _really_ want to be able * to do this check without having to look at inode->i_op, * so we keep a cache of "no, this doesn't need follow_link" * for the common case. */ static inline int should_follow_link(struct dentry *dentry, int follow) { return unlikely(d_is_symlink(dentry)) ? follow : 0; } static inline int walk_component(struct nameidata *nd, struct path *path, int follow) { struct inode *inode; int err; /* * "." and ".." are special - ".." especially so because it has * to be able to know about the current root directory and * parent relationships. */ if (unlikely(nd->last_type != LAST_NORM)) return handle_dots(nd, nd->last_type); err = lookup_fast(nd, path, &inode); if (unlikely(err)) { if (err < 0) goto out_err; err = lookup_slow(nd, path); if (err < 0) goto out_err; inode = path->dentry->d_inode; } err = -ENOENT; if (!inode || d_is_negative(path->dentry)) goto out_path_put; if (should_follow_link(path->dentry, follow)) { if (nd->flags & LOOKUP_RCU) { if (unlikely(unlazy_walk(nd, path->dentry))) { err = -ECHILD; goto out_err; } } BUG_ON(inode != path->dentry->d_inode); return 1; } path_to_nameidata(path, nd); nd->inode = inode; return 0; out_path_put: path_to_nameidata(path, nd); out_err: terminate_walk(nd); return err; } /* * This limits recursive symlink follows to 8, while * limiting consecutive symlinks to 40. * * Without that kind of total limit, nasty chains of consecutive * symlinks can cause almost arbitrarily long lookups. */ static inline int nested_symlink(struct path *path, struct nameidata *nd) { int res; if (unlikely(current->link_count >= MAX_NESTED_LINKS)) { path_put_conditional(path, nd); path_put(&nd->path); return -ELOOP; } BUG_ON(nd->depth >= MAX_NESTED_LINKS); nd->depth++; current->link_count++; do { struct path link = *path; void *cookie; res = follow_link(&link, nd, &cookie); if (res) break; res = walk_component(nd, path, LOOKUP_FOLLOW); put_link(nd, &link, cookie); } while (res > 0); current->link_count--; nd->depth--; return res; } /* * We can do the critical dentry name comparison and hashing * operations one word at a time, but we are limited to: * * - Architectures with fast unaligned word accesses. We could * do a "get_unaligned()" if this helps and is sufficiently * fast. * * - non-CONFIG_DEBUG_PAGEALLOC configurations (so that we * do not trap on the (extremely unlikely) case of a page * crossing operation. * * - Furthermore, we need an efficient 64-bit compile for the * 64-bit case in order to generate the "number of bytes in * the final mask". Again, that could be replaced with a * efficient population count instruction or similar. */ #ifdef CONFIG_DCACHE_WORD_ACCESS #include #ifdef CONFIG_64BIT static inline unsigned int fold_hash(unsigned long hash) { return hash_64(hash, 32); } #else /* 32-bit case */ #define fold_hash(x) (x) #endif unsigned int full_name_hash(const unsigned char *name, unsigned int len) { unsigned long a, mask; unsigned long hash = 0; for (;;) { a = load_unaligned_zeropad(name); if (len < sizeof(unsigned long)) break; hash += a; hash *= 9; name += sizeof(unsigned long); len -= sizeof(unsigned long); if (!len) goto done; } mask = bytemask_from_count(len); hash += mask & a; done: return fold_hash(hash); } EXPORT_SYMBOL(full_name_hash); /* * Calculate the length and hash of the path component, and * return the "hash_len" as the result. */ static inline u64 hash_name(const char *name) { unsigned long a, b, adata, bdata, mask, hash, len; const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; hash = a = 0; len = -sizeof(unsigned long); do { hash = (hash + a) * 9; len += sizeof(unsigned long); a = load_unaligned_zeropad(name+len); b = a ^ REPEAT_BYTE('/'); } while (!(has_zero(a, &adata, &constants) | has_zero(b, &bdata, &constants))); adata = prep_zero_mask(a, adata, &constants); bdata = prep_zero_mask(b, bdata, &constants); mask = create_zero_mask(adata | bdata); hash += a & zero_bytemask(mask); len += find_zero(mask); return hashlen_create(fold_hash(hash), len); } #else unsigned int full_name_hash(const unsigned char *name, unsigned int len) { unsigned long hash = init_name_hash(); while (len--) hash = partial_name_hash(*name++, hash); return end_name_hash(hash); } EXPORT_SYMBOL(full_name_hash); /* * We know there's a real path component here of at least * one character. */ static inline u64 hash_name(const char *name) { unsigned long hash = init_name_hash(); unsigned long len = 0, c; c = (unsigned char)*name; do { len++; hash = partial_name_hash(c, hash); c = (unsigned char)name[len]; } while (c && c != '/'); return hashlen_create(end_name_hash(hash), len); } #endif /* * Name resolution. * This is the basic name resolution function, turning a pathname into * the final dentry. We expect 'base' to be positive and a directory. * * Returns 0 and nd will have valid dentry and mnt on success. * Returns error and drops reference to input namei data on failure. */ static int link_path_walk(const char *name, struct nameidata *nd) { struct path next; int err; while (*name=='/') name++; if (!*name) return 0; /* At this point we know we have a real path component. */ for(;;) { u64 hash_len; int type; err = may_lookup(nd); if (err) break; hash_len = hash_name(name); type = LAST_NORM; if (name[0] == '.') switch (hashlen_len(hash_len)) { case 2: if (name[1] == '.') { type = LAST_DOTDOT; nd->flags |= LOOKUP_JUMPED; } break; case 1: type = LAST_DOT; } if (likely(type == LAST_NORM)) { struct dentry *parent = nd->path.dentry; nd->flags &= ~LOOKUP_JUMPED; if (unlikely(parent->d_flags & DCACHE_OP_HASH)) { struct qstr this = { { .hash_len = hash_len }, .name = name }; err = parent->d_op->d_hash(parent, &this); if (err < 0) break; hash_len = this.hash_len; name = this.name; } } nd->last.hash_len = hash_len; nd->last.name = name; nd->last_type = type; name += hashlen_len(hash_len); if (!*name) return 0; /* * If it wasn't NUL, we know it was '/'. Skip that * slash, and continue until no more slashes. */ do { name++; } while (unlikely(*name == '/')); if (!*name) return 0; err = walk_component(nd, &next, LOOKUP_FOLLOW); if (err < 0) return err; if (err) { err = nested_symlink(&next, nd); if (err) return err; } if (!d_can_lookup(nd->path.dentry)) { err = -ENOTDIR; break; } } terminate_walk(nd); return err; } static int path_init(int dfd, const char *name, unsigned int flags, struct nameidata *nd) { int retval = 0; nd->last_type = LAST_ROOT; /* if there are only slashes... */ nd->flags = flags | LOOKUP_JUMPED | LOOKUP_PARENT; nd->depth = 0; nd->base = NULL; if (flags & LOOKUP_ROOT) { struct dentry *root = nd->root.dentry; struct inode *inode = root->d_inode; if (*name) { if (!d_can_lookup(root)) return -ENOTDIR; retval = inode_permission(inode, MAY_EXEC); if (retval) return retval; } nd->path = nd->root; nd->inode = inode; if (flags & LOOKUP_RCU) { rcu_read_lock(); nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq); nd->m_seq = read_seqbegin(&mount_lock); } else { path_get(&nd->path); } goto done; } nd->root.mnt = NULL; nd->m_seq = read_seqbegin(&mount_lock); if (*name=='/') { if (flags & LOOKUP_RCU) { rcu_read_lock(); nd->seq = set_root_rcu(nd); } else { set_root(nd); path_get(&nd->root); } nd->path = nd->root; } else if (dfd == AT_FDCWD) { if (flags & LOOKUP_RCU) { struct fs_struct *fs = current->fs; unsigned seq; rcu_read_lock(); do { seq = read_seqcount_begin(&fs->seq); nd->path = fs->pwd; nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq); } while (read_seqcount_retry(&fs->seq, seq)); } else { get_fs_pwd(current->fs, &nd->path); } } else { /* Caller must check execute permissions on the starting path component */ struct fd f = fdget_raw(dfd); struct dentry *dentry; if (!f.file) return -EBADF; dentry = f.file->f_path.dentry; if (*name) { if (!d_can_lookup(dentry)) { fdput(f); return -ENOTDIR; } } nd->path = f.file->f_path; if (flags & LOOKUP_RCU) { if (f.flags & FDPUT_FPUT) nd->base = f.file; nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq); rcu_read_lock(); } else { path_get(&nd->path); fdput(f); } } nd->inode = nd->path.dentry->d_inode; if (!(flags & LOOKUP_RCU)) goto done; if (likely(!read_seqcount_retry(&nd->path.dentry->d_seq, nd->seq))) goto done; if (!(nd->flags & LOOKUP_ROOT)) nd->root.mnt = NULL; rcu_read_unlock(); return -ECHILD; done: current->total_link_count = 0; return link_path_walk(name, nd); } static void path_cleanup(struct nameidata *nd) { if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) { path_put(&nd->root); nd->root.mnt = NULL; } if (unlikely(nd->base)) fput(nd->base); } static inline int lookup_last(struct nameidata *nd, struct path *path) { if (nd->last_type == LAST_NORM && nd->last.name[nd->last.len]) nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY; nd->flags &= ~LOOKUP_PARENT; return walk_component(nd, path, nd->flags & LOOKUP_FOLLOW); } /* Returns 0 and nd will be valid on success; Retuns error, otherwise. */ static int path_lookupat(int dfd, const char *name, unsigned int flags, struct nameidata *nd) { struct path path; int err; /* * Path walking is largely split up into 2 different synchronisation * schemes, rcu-walk and ref-walk (explained in * Documentation/filesystems/path-lookup.txt). These share much of the * path walk code, but some things particularly setup, cleanup, and * following mounts are sufficiently divergent that functions are * duplicated. Typically there is a function foo(), and its RCU * analogue, foo_rcu(). * * -ECHILD is the error number of choice (just to avoid clashes) that * is returned if some aspect of an rcu-walk fails. Such an error must * be handled by restarting a traditional ref-walk (which will always * be able to complete). */ err = path_init(dfd, name, flags, nd); if (!err && !(flags & LOOKUP_PARENT)) { err = lookup_last(nd, &path); while (err > 0) { void *cookie; struct path link = path; err = may_follow_link(&link, nd); if (unlikely(err)) break; nd->flags |= LOOKUP_PARENT; err = follow_link(&link, nd, &cookie); if (err) break; err = lookup_last(nd, &path); put_link(nd, &link, cookie); } } if (!err) err = complete_walk(nd); if (!err && nd->flags & LOOKUP_DIRECTORY) { if (!d_can_lookup(nd->path.dentry)) { path_put(&nd->path); err = -ENOTDIR; } } path_cleanup(nd); return err; } static int filename_lookup(int dfd, struct filename *name, unsigned int flags, struct nameidata *nd) { int retval = path_lookupat(dfd, name->name, flags | LOOKUP_RCU, nd); if (unlikely(retval == -ECHILD)) retval = path_lookupat(dfd, name->name, flags, nd); if (unlikely(retval == -ESTALE)) retval = path_lookupat(dfd, name->name, flags | LOOKUP_REVAL, nd); if (likely(!retval)) audit_inode(name, nd->path.dentry, flags & LOOKUP_PARENT); return retval; } static int do_path_lookup(int dfd, const char *name, unsigned int flags, struct nameidata *nd) { struct filename filename = { .name = name }; return filename_lookup(dfd, &filename, flags, nd); } /* does lookup, returns the object with parent locked */ struct dentry *kern_path_locked(const char *name, struct path *path) { struct nameidata nd; struct dentry *d; int err = do_path_lookup(AT_FDCWD, name, LOOKUP_PARENT, &nd); if (err) return ERR_PTR(err); if (nd.last_type != LAST_NORM) { path_put(&nd.path); return ERR_PTR(-EINVAL); } mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT); d = __lookup_hash(&nd.last, nd.path.dentry, 0); if (IS_ERR(d)) { mutex_unlock(&nd.path.dentry->d_inode->i_mutex); path_put(&nd.path); return d; } *path = nd.path; return d; } int kern_path(const char *name, unsigned int flags, struct path *path) { struct nameidata nd; int res = do_path_lookup(AT_FDCWD, name, flags, &nd); if (!res) *path = nd.path; return res; } EXPORT_SYMBOL(kern_path); /** * vfs_path_lookup - lookup a file path relative to a dentry-vfsmount pair * @dentry: pointer to dentry of the base directory * @mnt: pointer to vfs mount of the base directory * @name: pointer to file name * @flags: lookup flags * @path: pointer to struct path to fill */ int vfs_path_lookup(struct dentry *dentry, struct vfsmount *mnt, const char *name, unsigned int flags, struct path *path) { struct nameidata nd; int err; nd.root.dentry = dentry; nd.root.mnt = mnt; BUG_ON(flags & LOOKUP_PARENT); /* the first argument of do_path_lookup() is ignored with LOOKUP_ROOT */ err = do_path_lookup(AT_FDCWD, name, flags | LOOKUP_ROOT, &nd); if (!err) *path = nd.path; return err; } EXPORT_SYMBOL(vfs_path_lookup); /* * Restricted form of lookup. Doesn't follow links, single-component only, * needs parent already locked. Doesn't follow mounts. * SMP-safe. */ static struct dentry *lookup_hash(struct nameidata *nd) { return __lookup_hash(&nd->last, nd->path.dentry, nd->flags); } /** * lookup_one_len - filesystem helper to lookup single pathname component * @name: pathname component to lookup * @base: base directory to lookup from * @len: maximum length @len should be interpreted to * * Note that this routine is purely a helper for filesystem usage and should * not be called by generic code. Also note that by using this function the * nameidata argument is passed to the filesystem methods and a filesystem * using this helper needs to be prepared for that. */ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len) { struct qstr this; unsigned int c; int err; WARN_ON_ONCE(!mutex_is_locked(&base->d_inode->i_mutex)); this.name = name; this.len = len; this.hash = full_name_hash(name, len); if (!len) return ERR_PTR(-EACCES); if (unlikely(name[0] == '.')) { if (len < 2 || (len == 2 && name[1] == '.')) return ERR_PTR(-EACCES); } while (len--) { c = *(const unsigned char *)name++; if (c == '/' || c == '\0') return ERR_PTR(-EACCES); } /* * See if the low-level filesystem might want * to use its own hash.. */ if (base->d_flags & DCACHE_OP_HASH) { int err = base->d_op->d_hash(base, &this); if (err < 0) return ERR_PTR(err); } err = inode_permission(base->d_inode, MAY_EXEC); if (err) return ERR_PTR(err); return __lookup_hash(&this, base, 0); } EXPORT_SYMBOL(lookup_one_len); int user_path_at_empty(int dfd, const char __user *name, unsigned flags, struct path *path, int *empty) { struct nameidata nd; struct filename *tmp = getname_flags(name, flags, empty); int err = PTR_ERR(tmp); if (!IS_ERR(tmp)) { BUG_ON(flags & LOOKUP_PARENT); err = filename_lookup(dfd, tmp, flags, &nd); putname(tmp); if (!err) *path = nd.path; } return err; } int user_path_at(int dfd, const char __user *name, unsigned flags, struct path *path) { return user_path_at_empty(dfd, name, flags, path, NULL); } EXPORT_SYMBOL(user_path_at); /* * NB: most callers don't do anything directly with the reference to the * to struct filename, but the nd->last pointer points into the name string * allocated by getname. So we must hold the reference to it until all * path-walking is complete. */ static struct filename * user_path_parent(int dfd, const char __user *path, struct nameidata *nd, unsigned int flags) { struct filename *s = getname(path); int error; /* only LOOKUP_REVAL is allowed in extra flags */ flags &= LOOKUP_REVAL; if (IS_ERR(s)) return s; error = filename_lookup(dfd, s, flags | LOOKUP_PARENT, nd); if (error) { putname(s); return ERR_PTR(error); } return s; } /** * mountpoint_last - look up last component for umount * @nd: pathwalk nameidata - currently pointing at parent directory of "last" * @path: pointer to container for result * * This is a special lookup_last function just for umount. In this case, we * need to resolve the path without doing any revalidation. * * The nameidata should be the result of doing a LOOKUP_PARENT pathwalk. Since * mountpoints are always pinned in the dcache, their ancestors are too. Thus, * in almost all cases, this lookup will be served out of the dcache. The only * cases where it won't are if nd->last refers to a symlink or the path is * bogus and it doesn't exist. * * Returns: * -error: if there was an error during lookup. This includes -ENOENT if the * lookup found a negative dentry. The nd->path reference will also be * put in this case. * * 0: if we successfully resolved nd->path and found it to not to be a * symlink that needs to be followed. "path" will also be populated. * The nd->path reference will also be put. * * 1: if we successfully resolved nd->last and found it to be a symlink * that needs to be followed. "path" will be populated with the path * to the link, and nd->path will *not* be put. */ static int mountpoint_last(struct nameidata *nd, struct path *path) { int error = 0; struct dentry *dentry; struct dentry *dir = nd->path.dentry; /* If we're in rcuwalk, drop out of it to handle last component */ if (nd->flags & LOOKUP_RCU) { if (unlazy_walk(nd, NULL)) { error = -ECHILD; goto out; } } nd->flags &= ~LOOKUP_PARENT; if (unlikely(nd->last_type != LAST_NORM)) { error = handle_dots(nd, nd->last_type); if (error) goto out; dentry = dget(nd->path.dentry); goto done; } mutex_lock(&dir->d_inode->i_mutex); dentry = d_lookup(dir, &nd->last); if (!dentry) { /* * No cached dentry. Mounted dentries are pinned in the cache, * so that means that this dentry is probably a symlink or the * path doesn't actually point to a mounted dentry. */ dentry = d_alloc(dir, &nd->last); if (!dentry) { error = -ENOMEM; mutex_unlock(&dir->d_inode->i_mutex); goto out; } dentry = lookup_real(dir->d_inode, dentry, nd->flags); error = PTR_ERR(dentry); if (IS_ERR(dentry)) { mutex_unlock(&dir->d_inode->i_mutex); goto out; } } mutex_unlock(&dir->d_inode->i_mutex); done: if (!dentry->d_inode || d_is_negative(dentry)) { error = -ENOENT; dput(dentry); goto out; } path->dentry = dentry; path->mnt = nd->path.mnt; if (should_follow_link(dentry, nd->flags & LOOKUP_FOLLOW)) return 1; mntget(path->mnt); follow_mount(path); error = 0; out: terminate_walk(nd); return error; } /** * path_mountpoint - look up a path to be umounted * @dfd: directory file descriptor to start walk from * @name: full pathname to walk * @path: pointer to container for result * @flags: lookup flags * * Look up the given name, but don't attempt to revalidate the last component. * Returns 0 and "path" will be valid on success; Returns error otherwise. */ static int path_mountpoint(int dfd, const char *name, struct path *path, unsigned int flags) { struct nameidata nd; int err; err = path_init(dfd, name, flags, &nd); if (unlikely(err)) goto out; err = mountpoint_last(&nd, path); while (err > 0) { void *cookie; struct path link = *path; err = may_follow_link(&link, &nd); if (unlikely(err)) break; nd.flags |= LOOKUP_PARENT; err = follow_link(&link, &nd, &cookie); if (err) break; err = mountpoint_last(&nd, path); put_link(&nd, &link, cookie); } out: path_cleanup(&nd); return err; } static int filename_mountpoint(int dfd, struct filename *s, struct path *path, unsigned int flags) { int error = path_mountpoint(dfd, s->name, path, flags | LOOKUP_RCU); if (unlikely(error == -ECHILD)) error = path_mountpoint(dfd, s->name, path, flags); if (unlikely(error == -ESTALE)) error = path_mountpoint(dfd, s->name, path, flags | LOOKUP_REVAL); if (likely(!error)) audit_inode(s, path->dentry, 0); return error; } /** * user_path_mountpoint_at - lookup a path from userland in order to umount it * @dfd: directory file descriptor * @name: pathname from userland * @flags: lookup flags * @path: pointer to container to hold result * * A umount is a special case for path walking. We're not actually interested * in the inode in this situation, and ESTALE errors can be a problem. We * simply want track down the dentry and vfsmount attached at the mountpoint * and avoid revalidating the last component. * * Returns 0 and populates "path" on success. */ int user_path_mountpoint_at(int dfd, const char __user *name, unsigned int flags, struct path *path) { struct filename *s = getname(name); int error; if (IS_ERR(s)) return PTR_ERR(s); error = filename_mountpoint(dfd, s, path, flags); putname(s); return error; } int kern_path_mountpoint(int dfd, const char *name, struct path *path, unsigned int flags) { struct filename s = {.name = name}; return filename_mountpoint(dfd, &s, path, flags); } EXPORT_SYMBOL(kern_path_mountpoint); int __check_sticky(struct inode *dir, struct inode *inode) { kuid_t fsuid = current_fsuid(); if (uid_eq(inode->i_uid, fsuid)) return 0; if (uid_eq(dir->i_uid, fsuid)) return 0; return !capable_wrt_inode_uidgid(inode, CAP_FOWNER); } EXPORT_SYMBOL(__check_sticky); /* * Check whether we can remove a link victim from directory dir, check * whether the type of victim is right. * 1. We can't do it if dir is read-only (done in permission()) * 2. We should have write and exec permissions on dir * 3. We can't remove anything from append-only dir * 4. We can't do anything with immutable dir (done in permission()) * 5. If the sticky bit on dir is set we should either * a. be owner of dir, or * b. be owner of victim, or * c. have CAP_FOWNER capability * 6. If the victim is append-only or immutable we can't do antyhing with * links pointing to it. * 7. If we were asked to remove a directory and victim isn't one - ENOTDIR. * 8. If we were asked to remove a non-directory and victim isn't one - EISDIR. * 9. We can't remove a root or mountpoint. * 10. We don't allow removal of NFS sillyrenamed files; it's handled by * nfs_async_unlink(). */ static int may_delete(struct inode *dir, struct dentry *victim, bool isdir) { struct inode *inode = victim->d_inode; int error; if (d_is_negative(victim)) return -ENOENT; BUG_ON(!inode); BUG_ON(victim->d_parent->d_inode != dir); audit_inode_child(dir, victim, AUDIT_TYPE_CHILD_DELETE); error = inode_permission(dir, MAY_WRITE | MAY_EXEC); if (error) return error; if (IS_APPEND(dir)) return -EPERM; if (check_sticky(dir, inode) || IS_APPEND(inode) || IS_IMMUTABLE(inode) || IS_SWAPFILE(inode)) return -EPERM; if (isdir) { if (!d_is_dir(victim)) return -ENOTDIR; if (IS_ROOT(victim)) return -EBUSY; } else if (d_is_dir(victim)) return -EISDIR; if (IS_DEADDIR(dir)) return -ENOENT; if (victim->d_flags & DCACHE_NFSFS_RENAMED) return -EBUSY; return 0; } /* Check whether we can create an object with dentry child in directory * dir. * 1. We can't do it if child already exists (open has special treatment for * this case, but since we are inlined it's OK) * 2. We can't do it if dir is read-only (done in permission()) * 3. We should have write and exec permissions on dir * 4. We can't do it if dir is immutable (done in permission()) */ static inline int may_create(struct inode *dir, struct dentry *child) { audit_inode_child(dir, child, AUDIT_TYPE_CHILD_CREATE); if (child->d_inode) return -EEXIST; if (IS_DEADDIR(dir)) return -ENOENT; return inode_permission(dir, MAY_WRITE | MAY_EXEC); } /* * p1 and p2 should be directories on the same fs. */ struct dentry *lock_rename(struct dentry *p1, struct dentry *p2) { struct dentry *p; if (p1 == p2) { mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT); return NULL; } mutex_lock(&p1->d_inode->i_sb->s_vfs_rename_mutex); p = d_ancestor(p2, p1); if (p) { mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_PARENT); mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_CHILD); return p; } p = d_ancestor(p1, p2); if (p) { mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT); mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_CHILD); return p; } mutex_lock_nested(&p1->d_inode->i_mutex, I_MUTEX_PARENT); mutex_lock_nested(&p2->d_inode->i_mutex, I_MUTEX_PARENT2); return NULL; } EXPORT_SYMBOL(lock_rename); void unlock_rename(struct dentry *p1, struct dentry *p2) { mutex_unlock(&p1->d_inode->i_mutex); if (p1 != p2) { mutex_unlock(&p2->d_inode->i_mutex); mutex_unlock(&p1->d_inode->i_sb->s_vfs_rename_mutex); } } EXPORT_SYMBOL(unlock_rename); int vfs_create(struct inode *dir, struct dentry *dentry, umode_t mode, bool want_excl) { int error = may_create(dir, dentry); if (error) return error; if (!dir->i_op->create) return -EACCES; /* shouldn't it be ENOSYS? */ mode &= S_IALLUGO; mode |= S_IFREG; error = security_inode_create(dir, dentry, mode); if (error) return error; error = dir->i_op->create(dir, dentry, mode, want_excl); if (!error) fsnotify_create(dir, dentry); return error; } EXPORT_SYMBOL(vfs_create); static int may_open(struct path *path, int acc_mode, int flag) { struct dentry *dentry = path->dentry; struct inode *inode = dentry->d_inode; int error; /* O_PATH? */ if (!acc_mode) return 0; if (!inode) return -ENOENT; switch (inode->i_mode & S_IFMT) { case S_IFLNK: return -ELOOP; case S_IFDIR: if (acc_mode & MAY_WRITE) return -EISDIR; break; case S_IFBLK: case S_IFCHR: if (path->mnt->mnt_flags & MNT_NODEV) return -EACCES; /*FALLTHRU*/ case S_IFIFO: case S_IFSOCK: flag &= ~O_TRUNC; break; } error = inode_permission(inode, acc_mode); if (error) return error; /* * An append-only file must be opened in append mode for writing. */ if (IS_APPEND(inode)) { if ((flag & O_ACCMODE) != O_RDONLY && !(flag & O_APPEND)) return -EPERM; if (flag & O_TRUNC) return -EPERM; } /* O_NOATIME can only be set by the owner or superuser */ if (flag & O_NOATIME && !inode_owner_or_capable(inode)) return -EPERM; return 0; } static int handle_truncate(struct file *filp) { struct path *path = &filp->f_path; struct inode *inode = path->dentry->d_inode; int error = get_write_access(inode); if (error) return error; /* * Refuse to truncate files with mandatory locks held on them. */ error = locks_verify_locked(filp); if (!error) error = security_path_truncate(path); if (!error) { error = do_truncate(path->dentry, 0, ATTR_MTIME|ATTR_CTIME|ATTR_OPEN, filp); } put_write_access(inode); return error; } static inline int open_to_namei_flags(int flag) { if ((flag & O_ACCMODE) == 3) flag--; return flag; } static int may_o_create(struct path *dir, struct dentry *dentry, umode_t mode) { int error = security_path_mknod(dir, dentry, mode, 0); if (error) return error; error = inode_permission(dir->dentry->d_inode, MAY_WRITE | MAY_EXEC); if (error) return error; return security_inode_create(dir->dentry->d_inode, dentry, mode); } /* * Attempt to atomically look up, create and open a file from a negative * dentry. * * Returns 0 if successful. The file will have been created and attached to * @file by the filesystem calling finish_open(). * * Returns 1 if the file was looked up only or didn't need creating. The * caller will need to perform the open themselves. @path will have been * updated to point to the new dentry. This may be negative. * * Returns an error code otherwise. */ static int atomic_open(struct nameidata *nd, struct dentry *dentry, struct path *path, struct file *file, const struct open_flags *op, bool got_write, bool need_lookup, int *opened) { struct inode *dir = nd->path.dentry->d_inode; unsigned open_flag = open_to_namei_flags(op->open_flag); umode_t mode; int error; int acc_mode; int create_error = 0; struct dentry *const DENTRY_NOT_SET = (void *) -1UL; bool excl; BUG_ON(dentry->d_inode); /* Don't create child dentry for a dead directory. */ if (unlikely(IS_DEADDIR(dir))) { error = -ENOENT; goto out; } mode = op->mode; if ((open_flag & O_CREAT) && !IS_POSIXACL(dir)) mode &= ~current_umask(); excl = (open_flag & (O_EXCL | O_CREAT)) == (O_EXCL | O_CREAT); if (excl) open_flag &= ~O_TRUNC; /* * Checking write permission is tricky, bacuse we don't know if we are * going to actually need it: O_CREAT opens should work as long as the * file exists. But checking existence breaks atomicity. The trick is * to check access and if not granted clear O_CREAT from the flags. * * Another problem is returing the "right" error value (e.g. for an * O_EXCL open we want to return EEXIST not EROFS). */ if (((open_flag & (O_CREAT | O_TRUNC)) || (open_flag & O_ACCMODE) != O_RDONLY) && unlikely(!got_write)) { if (!(open_flag & O_CREAT)) { /* * No O_CREATE -> atomicity not a requirement -> fall * back to lookup + open */ goto no_open; } else if (open_flag & (O_EXCL | O_TRUNC)) { /* Fall back and fail with the right error */ create_error = -EROFS; goto no_open; } else { /* No side effects, safe to clear O_CREAT */ create_error = -EROFS; open_flag &= ~O_CREAT; } } if (open_flag & O_CREAT) { error = may_o_create(&nd->path, dentry, mode); if (error) { create_error = error; if (open_flag & O_EXCL) goto no_open; open_flag &= ~O_CREAT; } } if (nd->flags & LOOKUP_DIRECTORY) open_flag |= O_DIRECTORY; file->f_path.dentry = DENTRY_NOT_SET; file->f_path.mnt = nd->path.mnt; error = dir->i_op->atomic_open(dir, dentry, file, open_flag, mode, opened); if (error < 0) { if (create_error && error == -ENOENT) error = create_error; goto out; } if (error) { /* returned 1, that is */ if (WARN_ON(file->f_path.dentry == DENTRY_NOT_SET)) { error = -EIO; goto out; } if (file->f_path.dentry) { dput(dentry); dentry = file->f_path.dentry; } if (*opened & FILE_CREATED) fsnotify_create(dir, dentry); if (!dentry->d_inode) { WARN_ON(*opened & FILE_CREATED); if (create_error) { error = create_error; goto out; } } else { if (excl && !(*opened & FILE_CREATED)) { error = -EEXIST; goto out; } } goto looked_up; } /* * We didn't have the inode before the open, so check open permission * here. */ acc_mode = op->acc_mode; if (*opened & FILE_CREATED) { WARN_ON(!(open_flag & O_CREAT)); fsnotify_create(dir, dentry); acc_mode = MAY_OPEN; } error = may_open(&file->f_path, acc_mode, open_flag); if (error) fput(file); out: dput(dentry); return error; no_open: if (need_lookup) { dentry = lookup_real(dir, dentry, nd->flags); if (IS_ERR(dentry)) return PTR_ERR(dentry); if (create_error) { int open_flag = op->open_flag; error = create_error; if ((open_flag & O_EXCL)) { if (!dentry->d_inode) goto out; } else if (!dentry->d_inode) { goto out; } else if ((open_flag & O_TRUNC) && S_ISREG(dentry->d_inode->i_mode)) { goto out; } /* will fail later, go on to get the right error */ } } looked_up: path->dentry = dentry; path->mnt = nd->path.mnt; return 1; } /* * Look up and maybe create and open the last component. * * Must be called with i_mutex held on parent. * * Returns 0 if the file was successfully atomically created (if necessary) and * opened. In this case the file will be returned attached to @file. * * Returns 1 if the file was not completely opened at this time, though lookups * and creations will have been performed and the dentry returned in @path will * be positive upon return if O_CREAT was specified. If O_CREAT wasn't * specified then a negative dentry may be returned. * * An error code is returned otherwise. * * FILE_CREATE will be set in @*opened if the dentry was created and will be * cleared otherwise prior to returning. */ static int lookup_open(struct nameidata *nd, struct path *path, struct file *file, const struct open_flags *op, bool got_write, int *opened) { struct dentry *dir = nd->path.dentry; struct inode *dir_inode = dir->d_inode; struct dentry *dentry; int error; bool need_lookup; *opened &= ~FILE_CREATED; dentry = lookup_dcache(&nd->last, dir, nd->flags, &need_lookup); if (IS_ERR(dentry)) return PTR_ERR(dentry); /* Cached positive dentry: will open in f_op->open */ if (!need_lookup && dentry->d_inode) goto out_no_open; if ((nd->flags & LOOKUP_OPEN) && dir_inode->i_op->atomic_open) { return atomic_open(nd, dentry, path, file, op, got_write, need_lookup, opened); } if (need_lookup) { BUG_ON(dentry->d_inode); dentry = lookup_real(dir_inode, dentry, nd->flags); if (IS_ERR(dentry)) return PTR_ERR(dentry); } /* Negative dentry, just create the file */ if (!dentry->d_inode && (op->open_flag & O_CREAT)) { umode_t mode = op->mode; if (!IS_POSIXACL(dir->d_inode)) mode &= ~current_umask(); /* * This write is needed to ensure that a * rw->ro transition does not occur between * the time when the file is created and when * a permanent write count is taken through * the 'struct file' in finish_open(). */ if (!got_write) { error = -EROFS; goto out_dput; } *opened |= FILE_CREATED; error = security_path_mknod(&nd->path, dentry, mode, 0); if (error) goto out_dput; error = vfs_create(dir->d_inode, dentry, mode, nd->flags & LOOKUP_EXCL); if (error) goto out_dput; } out_no_open: path->dentry = dentry; path->mnt = nd->path.mnt; return 1; out_dput: dput(dentry); return error; } /* * Handle the last step of open() */ static int do_last(struct nameidata *nd, struct path *path, struct file *file, const struct open_flags *op, int *opened, struct filename *name) { struct dentry *dir = nd->path.dentry; int open_flag = op->open_flag; bool will_truncate = (open_flag & O_TRUNC) != 0; bool got_write = false; int acc_mode = op->acc_mode; struct inode *inode; bool symlink_ok = false; struct path save_parent = { .dentry = NULL, .mnt = NULL }; bool retried = false; int error; nd->flags &= ~LOOKUP_PARENT; nd->flags |= op->intent; if (nd->last_type != LAST_NORM) { error = handle_dots(nd, nd->last_type); if (error) return error; goto finish_open; } if (!(open_flag & O_CREAT)) { if (nd->last.name[nd->last.len]) nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY; if (open_flag & O_PATH && !(nd->flags & LOOKUP_FOLLOW)) symlink_ok = true; /* we _can_ be in RCU mode here */ error = lookup_fast(nd, path, &inode); if (likely(!error)) goto finish_lookup; if (error < 0) goto out; BUG_ON(nd->inode != dir->d_inode); } else { /* create side of things */ /* * This will *only* deal with leaving RCU mode - LOOKUP_JUMPED * has been cleared when we got to the last component we are * about to look up */ error = complete_walk(nd); if (error) return error; audit_inode(name, dir, LOOKUP_PARENT); error = -EISDIR; /* trailing slashes? */ if (nd->last.name[nd->last.len]) goto out; } retry_lookup: if (op->open_flag & (O_CREAT | O_TRUNC | O_WRONLY | O_RDWR)) { error = mnt_want_write(nd->path.mnt); if (!error) got_write = true; /* * do _not_ fail yet - we might not need that or fail with * a different error; let lookup_open() decide; we'll be * dropping this one anyway. */ } mutex_lock(&dir->d_inode->i_mutex); error = lookup_open(nd, path, file, op, got_write, opened); mutex_unlock(&dir->d_inode->i_mutex); if (error <= 0) { if (error) goto out; if ((*opened & FILE_CREATED) || !S_ISREG(file_inode(file)->i_mode)) will_truncate = false; audit_inode(name, file->f_path.dentry, 0); goto opened; } if (*opened & FILE_CREATED) { /* Don't check for write permission, don't truncate */ open_flag &= ~O_TRUNC; will_truncate = false; acc_mode = MAY_OPEN; path_to_nameidata(path, nd); goto finish_open_created; } /* * create/update audit record if it already exists. */ if (d_is_positive(path->dentry)) audit_inode(name, path->dentry, 0); /* * If atomic_open() acquired write access it is dropped now due to * possible mount and symlink following (this might be optimized away if * necessary...) */ if (got_write) { mnt_drop_write(nd->path.mnt); got_write = false; } error = -EEXIST; if ((open_flag & (O_EXCL | O_CREAT)) == (O_EXCL | O_CREAT)) goto exit_dput; error = follow_managed(path, nd->flags); if (error < 0) goto exit_dput; if (error) nd->flags |= LOOKUP_JUMPED; BUG_ON(nd->flags & LOOKUP_RCU); inode = path->dentry->d_inode; finish_lookup: /* we _can_ be in RCU mode here */ error = -ENOENT; if (!inode || d_is_negative(path->dentry)) { path_to_nameidata(path, nd); goto out; } if (should_follow_link(path->dentry, !symlink_ok)) { if (nd->flags & LOOKUP_RCU) { if (unlikely(unlazy_walk(nd, path->dentry))) { error = -ECHILD; goto out; } } BUG_ON(inode != path->dentry->d_inode); return 1; } if ((nd->flags & LOOKUP_RCU) || nd->path.mnt != path->mnt) { path_to_nameidata(path, nd); } else { save_parent.dentry = nd->path.dentry; save_parent.mnt = mntget(path->mnt); nd->path.dentry = path->dentry; } nd->inode = inode; /* Why this, you ask? _Now_ we might have grown LOOKUP_JUMPED... */ finish_open: error = complete_walk(nd); if (error) { path_put(&save_parent); return error; } audit_inode(name, nd->path.dentry, 0); error = -EISDIR; if ((open_flag & O_CREAT) && d_is_dir(nd->path.dentry)) goto out; error = -ENOTDIR; if ((nd->flags & LOOKUP_DIRECTORY) && !d_can_lookup(nd->path.dentry)) goto out; if (!S_ISREG(nd->inode->i_mode)) will_truncate = false; if (will_truncate) { error = mnt_want_write(nd->path.mnt); if (error) goto out; got_write = true; } finish_open_created: error = may_open(&nd->path, acc_mode, open_flag); if (error) goto out; BUG_ON(*opened & FILE_OPENED); /* once it's opened, it's opened */ error = vfs_open(&nd->path, file, current_cred()); if (!error) { *opened |= FILE_OPENED; } else { if (error == -EOPENSTALE) goto stale_open; goto out; } opened: error = open_check_o_direct(file); if (error) goto exit_fput; error = ima_file_check(file, op->acc_mode, *opened); if (error) goto exit_fput; if (will_truncate) { error = handle_truncate(file); if (error) goto exit_fput; } out: if (got_write) mnt_drop_write(nd->path.mnt); path_put(&save_parent); terminate_walk(nd); return error; exit_dput: path_put_conditional(path, nd); goto out; exit_fput: fput(file); goto out; stale_open: /* If no saved parent or already retried then can't retry */ if (!save_parent.dentry || retried) goto out; BUG_ON(save_parent.dentry != dir); path_put(&nd->path); nd->path = save_parent; nd->inode = dir->d_inode; save_parent.mnt = NULL; save_parent.dentry = NULL; if (got_write) { mnt_drop_write(nd->path.mnt); got_write = false; } retried = true; goto retry_lookup; } static int do_tmpfile(int dfd, struct filename *pathname, struct nameidata *nd, int flags, const struct open_flags *op, struct file *file, int *opened) { static const struct qstr name = QSTR_INIT("/", 1); struct dentry *dentry, *child; struct inode *dir; int error = path_lookupat(dfd, pathname->name, flags | LOOKUP_DIRECTORY, nd); if (unlikely(error)) return error; error = mnt_want_write(nd->path.mnt); if (unlikely(error)) goto out; /* we want directory to be writable */ error = inode_permission(nd->inode, MAY_WRITE | MAY_EXEC); if (error) goto out2; dentry = nd->path.dentry; dir = dentry->d_inode; if (!dir->i_op->tmpfile) { error = -EOPNOTSUPP; goto out2; } child = d_alloc(dentry, &name); if (unlikely(!child)) { error = -ENOMEM; goto out2; } nd->flags &= ~LOOKUP_DIRECTORY; nd->flags |= op->intent; dput(nd->path.dentry); nd->path.dentry = child; error = dir->i_op->tmpfile(dir, nd->path.dentry, op->mode); if (error) goto out2; audit_inode(pathname, nd->path.dentry, 0); /* Don't check for other permissions, the inode was just created */ error = may_open(&nd->path, MAY_OPEN, op->open_flag); if (error) goto out2; file->f_path.mnt = nd->path.mnt; error = finish_open(file, nd->path.dentry, NULL, opened); if (error) goto out2; error = open_check_o_direct(file); if (error) { fput(file); } else if (!(op->open_flag & O_EXCL)) { struct inode *inode = file_inode(file); spin_lock(&inode->i_lock); inode->i_state |= I_LINKABLE; spin_unlock(&inode->i_lock); } out2: mnt_drop_write(nd->path.mnt); out: path_put(&nd->path); return error; } static struct file *path_openat(int dfd, struct filename *pathname, struct nameidata *nd, const struct open_flags *op, int flags) { struct file *file; struct path path; int opened = 0; int error; file = get_empty_filp(); if (IS_ERR(file)) return file; file->f_flags = op->open_flag; if (unlikely(file->f_flags & __O_TMPFILE)) { error = do_tmpfile(dfd, pathname, nd, flags, op, file, &opened); goto out; } error = path_init(dfd, pathname->name, flags, nd); if (unlikely(error)) goto out; error = do_last(nd, &path, file, op, &opened, pathname); while (unlikely(error > 0)) { /* trailing symlink */ struct path link = path; void *cookie; if (!(nd->flags & LOOKUP_FOLLOW)) { path_put_conditional(&path, nd); path_put(&nd->path); error = -ELOOP; break; } error = may_follow_link(&link, nd); if (unlikely(error)) break; nd->flags |= LOOKUP_PARENT; nd->flags &= ~(LOOKUP_OPEN|LOOKUP_CREATE|LOOKUP_EXCL); error = follow_link(&link, nd, &cookie); if (unlikely(error)) break; error = do_last(nd, &path, file, op, &opened, pathname); put_link(nd, &link, cookie); } out: path_cleanup(nd); if (!(opened & FILE_OPENED)) { BUG_ON(!error); put_filp(file); } if (unlikely(error)) { if (error == -EOPENSTALE) { if (flags & LOOKUP_RCU) error = -ECHILD; else error = -ESTALE; } file = ERR_PTR(error); } return file; } struct file *do_filp_open(int dfd, struct filename *pathname, const struct open_flags *op) { struct nameidata nd; int flags = op->lookup_flags; struct file *filp; filp = path_openat(dfd, pathname, &nd, op, flags | LOOKUP_RCU); if (unlikely(filp == ERR_PTR(-ECHILD))) filp = path_openat(dfd, pathname, &nd, op, flags); if (unlikely(filp == ERR_PTR(-ESTALE))) filp = path_openat(dfd, pathname, &nd, op, flags | LOOKUP_REVAL); return filp; } struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt, const char *name, const struct open_flags *op) { struct nameidata nd; struct file *file; struct filename filename = { .name = name }; int flags = op->lookup_flags | LOOKUP_ROOT; nd.root.mnt = mnt; nd.root.dentry = dentry; if (d_is_symlink(dentry) && op->intent & LOOKUP_OPEN) return ERR_PTR(-ELOOP); file = path_openat(-1, &filename, &nd, op, flags | LOOKUP_RCU); if (unlikely(file == ERR_PTR(-ECHILD))) file = path_openat(-1, &filename, &nd, op, flags); if (unlikely(file == ERR_PTR(-ESTALE))) file = path_openat(-1, &filename, &nd, op, flags | LOOKUP_REVAL); return file; } struct dentry *kern_path_create(int dfd, const char *pathname, struct path *path, unsigned int lookup_flags) { struct dentry *dentry = ERR_PTR(-EEXIST); struct nameidata nd; int err2; int error; bool is_dir = (lookup_flags & LOOKUP_DIRECTORY); /* * Note that only LOOKUP_REVAL and LOOKUP_DIRECTORY matter here. Any * other flags passed in are ignored! */ lookup_flags &= LOOKUP_REVAL; error = do_path_lookup(dfd, pathname, LOOKUP_PARENT|lookup_flags, &nd); if (error) return ERR_PTR(error); /* * Yucky last component or no last component at all? * (foo/., foo/.., /////) */ if (nd.last_type != LAST_NORM) goto out; nd.flags &= ~LOOKUP_PARENT; nd.flags |= LOOKUP_CREATE | LOOKUP_EXCL; /* don't fail immediately if it's r/o, at least try to report other errors */ err2 = mnt_want_write(nd.path.mnt); /* * Do the final lookup. */ mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT); dentry = lookup_hash(&nd); if (IS_ERR(dentry)) goto unlock; error = -EEXIST; if (d_is_positive(dentry)) goto fail; /* * Special case - lookup gave negative, but... we had foo/bar/ * From the vfs_mknod() POV we just have a negative dentry - * all is fine. Let's be bastards - you had / on the end, you've * been asking for (non-existent) directory. -ENOENT for you. */ if (unlikely(!is_dir && nd.last.name[nd.last.len])) { error = -ENOENT; goto fail; } if (unlikely(err2)) { error = err2; goto fail; } *path = nd.path; return dentry; fail: dput(dentry); dentry = ERR_PTR(error); unlock: mutex_unlock(&nd.path.dentry->d_inode->i_mutex); if (!err2) mnt_drop_write(nd.path.mnt); out: path_put(&nd.path); return dentry; } EXPORT_SYMBOL(kern_path_create); void done_path_create(struct path *path, struct dentry *dentry) { dput(dentry); mutex_unlock(&path->dentry->d_inode->i_mutex); mnt_drop_write(path->mnt); path_put(path); } EXPORT_SYMBOL(done_path_create); struct dentry *user_path_create(int dfd, const char __user *pathname, struct path *path, unsigned int lookup_flags) { struct filename *tmp = getname(pathname); struct dentry *res; if (IS_ERR(tmp)) return ERR_CAST(tmp); res = kern_path_create(dfd, tmp->name, path, lookup_flags); putname(tmp); return res; } EXPORT_SYMBOL(user_path_create); int vfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev) { int error = may_create(dir, dentry); if (error) return error; if ((S_ISCHR(mode) || S_ISBLK(mode)) && !capable(CAP_MKNOD)) return -EPERM; if (!dir->i_op->mknod) return -EPERM; error = devcgroup_inode_mknod(mode, dev); if (error) return error; error = security_inode_mknod(dir, dentry, mode, dev); if (error) return error; error = dir->i_op->mknod(dir, dentry, mode, dev); if (!error) fsnotify_create(dir, dentry); return error; } EXPORT_SYMBOL(vfs_mknod); static int may_mknod(umode_t mode) { switch (mode & S_IFMT) { case S_IFREG: case S_IFCHR: case S_IFBLK: case S_IFIFO: case S_IFSOCK: case 0: /* zero mode translates to S_IFREG */ return 0; case S_IFDIR: return -EPERM; default: return -EINVAL; } } SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode, unsigned, dev) { struct dentry *dentry; struct path path; int error; unsigned int lookup_flags = 0; error = may_mknod(mode); if (error) return error; retry: dentry = user_path_create(dfd, filename, &path, lookup_flags); if (IS_ERR(dentry)) return PTR_ERR(dentry); if (!IS_POSIXACL(path.dentry->d_inode)) mode &= ~current_umask(); error = security_path_mknod(&path, dentry, mode, dev); if (error) goto out; switch (mode & S_IFMT) { case 0: case S_IFREG: error = vfs_create(path.dentry->d_inode,dentry,mode,true); break; case S_IFCHR: case S_IFBLK: error = vfs_mknod(path.dentry->d_inode,dentry,mode, new_decode_dev(dev)); break; case S_IFIFO: case S_IFSOCK: error = vfs_mknod(path.dentry->d_inode,dentry,mode,0); break; } out: done_path_create(&path, dentry); if (retry_estale(error, lookup_flags)) { lookup_flags |= LOOKUP_REVAL; goto retry; } return error; } SYSCALL_DEFINE3(mknod, const char __user *, filename, umode_t, mode, unsigned, dev) { return sys_mknodat(AT_FDCWD, filename, mode, dev); } int vfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode) { int error = may_create(dir, dentry); unsigned max_links = dir->i_sb->s_max_links; if (error) return error; if (!dir->i_op->mkdir) return -EPERM; mode &= (S_IRWXUGO|S_ISVTX); error = security_inode_mkdir(dir, dentry, mode); if (error) return error; if (max_links && dir->i_nlink >= max_links) return -EMLINK; error = dir->i_op->mkdir(dir, dentry, mode); if (!error) fsnotify_mkdir(dir, dentry); return error; } EXPORT_SYMBOL(vfs_mkdir); SYSCALL_DEFINE3(mkdirat, int, dfd, const char __user *, pathname, umode_t, mode) { struct dentry *dentry; struct path path; int error; unsigned int lookup_flags = LOOKUP_DIRECTORY; retry: dentry = user_path_create(dfd, pathname, &path, lookup_flags); if (IS_ERR(dentry)) return PTR_ERR(dentry); if (!IS_POSIXACL(path.dentry->d_inode)) mode &= ~current_umask(); error = security_path_mkdir(&path, dentry, mode); if (!error) error = vfs_mkdir(path.dentry->d_inode, dentry, mode); done_path_create(&path, dentry); if (retry_estale(error, lookup_flags)) { lookup_flags |= LOOKUP_REVAL; goto retry; } return error; } SYSCALL_DEFINE2(mkdir, const char __user *, pathname, umode_t, mode) { return sys_mkdirat(AT_FDCWD, pathname, mode); } /* * The dentry_unhash() helper will try to drop the dentry early: we * should have a usage count of 1 if we're the only user of this * dentry, and if that is true (possibly after pruning the dcache), * then we drop the dentry now. * * A low-level filesystem can, if it choses, legally * do a * * if (!d_unhashed(dentry)) * return -EBUSY; * * if it cannot handle the case of removing a directory * that is still in use by something else.. */ void dentry_unhash(struct dentry *dentry) { shrink_dcache_parent(dentry); spin_lock(&dentry->d_lock); if (dentry->d_lockref.count == 1) __d_drop(dentry); spin_unlock(&dentry->d_lock); } EXPORT_SYMBOL(dentry_unhash); int vfs_rmdir(struct inode *dir, struct dentry *dentry) { int error = may_delete(dir, dentry, 1); if (error) return error; if (!dir->i_op->rmdir) return -EPERM; dget(dentry); mutex_lock(&dentry->d_inode->i_mutex); error = -EBUSY; if (is_local_mountpoint(dentry)) goto out; error = security_inode_rmdir(dir, dentry); if (error) goto out; shrink_dcache_parent(dentry); error = dir->i_op->rmdir(dir, dentry); if (error) goto out; dentry->d_inode->i_flags |= S_DEAD; dont_mount(dentry); detach_mounts(dentry); out: mutex_unlock(&dentry->d_inode->i_mutex); dput(dentry); if (!error) d_delete(dentry); return error; } EXPORT_SYMBOL(vfs_rmdir); static long do_rmdir(int dfd, const char __user *pathname) { int error = 0; struct filename *name; struct dentry *dentry; struct nameidata nd; unsigned int lookup_flags = 0; retry: name = user_path_parent(dfd, pathname, &nd, lookup_flags); if (IS_ERR(name)) return PTR_ERR(name); switch(nd.last_type) { case LAST_DOTDOT: error = -ENOTEMPTY; goto exit1; case LAST_DOT: error = -EINVAL; goto exit1; case LAST_ROOT: error = -EBUSY; goto exit1; } nd.flags &= ~LOOKUP_PARENT; error = mnt_want_write(nd.path.mnt); if (error) goto exit1; mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT); dentry = lookup_hash(&nd); error = PTR_ERR(dentry); if (IS_ERR(dentry)) goto exit2; if (!dentry->d_inode) { error = -ENOENT; goto exit3; } error = security_path_rmdir(&nd.path, dentry); if (error) goto exit3; error = vfs_rmdir(nd.path.dentry->d_inode, dentry); exit3: dput(dentry); exit2: mutex_unlock(&nd.path.dentry->d_inode->i_mutex); mnt_drop_write(nd.path.mnt); exit1: path_put(&nd.path); putname(name); if (retry_estale(error, lookup_flags)) { lookup_flags |= LOOKUP_REVAL; goto retry; } return error; } SYSCALL_DEFINE1(rmdir, const char __user *, pathname) { return do_rmdir(AT_FDCWD, pathname); } /** * vfs_unlink - unlink a filesystem object * @dir: parent directory * @dentry: victim * @delegated_inode: returns victim inode, if the inode is delegated. * * The caller must hold dir->i_mutex. * * If vfs_unlink discovers a delegation, it will return -EWOULDBLOCK and * return a reference to the inode in delegated_inode. The caller * should then break the delegation on that inode and retry. Because * breaking a delegation may take a long time, the caller should drop * dir->i_mutex before doing so. * * Alternatively, a caller may pass NULL for delegated_inode. This may * be appropriate for callers that expect the underlying filesystem not * to be NFS exported. */ int vfs_unlink(struct inode *dir, struct dentry *dentry, struct inode **delegated_inode) { struct inode *target = dentry->d_inode; int error = may_delete(dir, dentry, 0); if (error) return error; if (!dir->i_op->unlink) return -EPERM; mutex_lock(&target->i_mutex); if (is_local_mountpoint(dentry)) error = -EBUSY; else { error = security_inode_unlink(dir, dentry); if (!error) { error = try_break_deleg(target, delegated_inode); if (error) goto out; error = dir->i_op->unlink(dir, dentry); if (!error) { dont_mount(dentry); detach_mounts(dentry); } } } out: mutex_unlock(&target->i_mutex); /* We don't d_delete() NFS sillyrenamed files--they still exist. */ if (!error && !(dentry->d_flags & DCACHE_NFSFS_RENAMED)) { fsnotify_link_count(target); d_delete(dentry); } return error; } EXPORT_SYMBOL(vfs_unlink); /* * Make sure that the actual truncation of the file will occur outside its * directory's i_mutex. Truncate can take a long time if there is a lot of * writeout happening, and we don't want to prevent access to the directory * while waiting on the I/O. */ static long do_unlinkat(int dfd, const char __user *pathname) { int error; struct filename *name; struct dentry *dentry; struct nameidata nd; struct inode *inode = NULL; struct inode *delegated_inode = NULL; unsigned int lookup_flags = 0; retry: name = user_path_parent(dfd, pathname, &nd, lookup_flags); if (IS_ERR(name)) return PTR_ERR(name); error = -EISDIR; if (nd.last_type != LAST_NORM) goto exit1; nd.flags &= ~LOOKUP_PARENT; error = mnt_want_write(nd.path.mnt); if (error) goto exit1; retry_deleg: mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT); dentry = lookup_hash(&nd); error = PTR_ERR(dentry); if (!IS_ERR(dentry)) { /* Why not before? Because we want correct error value */ if (nd.last.name[nd.last.len]) goto slashes; inode = dentry->d_inode; if (d_is_negative(dentry)) goto slashes; ihold(inode); error = security_path_unlink(&nd.path, dentry); if (error) goto exit2; error = vfs_unlink(nd.path.dentry->d_inode, dentry, &delegated_inode); exit2: dput(dentry); } mutex_unlock(&nd.path.dentry->d_inode->i_mutex); if (inode) iput(inode); /* truncate the inode here */ inode = NULL; if (delegated_inode) { error = break_deleg_wait(&delegated_inode); if (!error) goto retry_deleg; } mnt_drop_write(nd.path.mnt); exit1: path_put(&nd.path); putname(name); if (retry_estale(error, lookup_flags)) { lookup_flags |= LOOKUP_REVAL; inode = NULL; goto retry; } return error; slashes: if (d_is_negative(dentry)) error = -ENOENT; else if (d_is_dir(dentry)) error = -EISDIR; else error = -ENOTDIR; goto exit2; } SYSCALL_DEFINE3(unlinkat, int, dfd, const char __user *, pathname, int, flag) { if ((flag & ~AT_REMOVEDIR) != 0) return -EINVAL; if (flag & AT_REMOVEDIR) return do_rmdir(dfd, pathname); return do_unlinkat(dfd, pathname); } SYSCALL_DEFINE1(unlink, const char __user *, pathname) { return do_unlinkat(AT_FDCWD, pathname); } int vfs_symlink(struct inode *dir, struct dentry *dentry, const char *oldname) { int error = may_create(dir, dentry); if (error) return error; if (!dir->i_op->symlink) return -EPERM; error = security_inode_symlink(dir, dentry, oldname); if (error) return error; error = dir->i_op->symlink(dir, dentry, oldname); if (!error) fsnotify_create(dir, dentry); return error; } EXPORT_SYMBOL(vfs_symlink); SYSCALL_DEFINE3(symlinkat, const char __user *, oldname, int, newdfd, const char __user *, newname) { int error; struct filename *from; struct dentry *dentry; struct path path; unsigned int lookup_flags = 0; from = getname(oldname); if (IS_ERR(from)) return PTR_ERR(from); retry: dentry = user_path_create(newdfd, newname, &path, lookup_flags); error = PTR_ERR(dentry); if (IS_ERR(dentry)) goto out_putname; error = security_path_symlink(&path, dentry, from->name); if (!error) error = vfs_symlink(path.dentry->d_inode, dentry, from->name); done_path_create(&path, dentry); if (retry_estale(error, lookup_flags)) { lookup_flags |= LOOKUP_REVAL; goto retry; } out_putname: putname(from); return error; } SYSCALL_DEFINE2(symlink, const char __user *, oldname, const char __user *, newname) { return sys_symlinkat(oldname, AT_FDCWD, newname); } /** * vfs_link - create a new link * @old_dentry: object to be linked * @dir: new parent * @new_dentry: where to create the new link * @delegated_inode: returns inode needing a delegation break * * The caller must hold dir->i_mutex * * If vfs_link discovers a delegation on the to-be-linked file in need * of breaking, it will return -EWOULDBLOCK and return a reference to the * inode in delegated_inode. The caller should then break the delegation * and retry. Because breaking a delegation may take a long time, the * caller should drop the i_mutex before doing so. * * Alternatively, a caller may pass NULL for delegated_inode. This may * be appropriate for callers that expect the underlying filesystem not * to be NFS exported. */ int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_dentry, struct inode **delegated_inode) { struct inode *inode = old_dentry->d_inode; unsigned max_links = dir->i_sb->s_max_links; int error; if (!inode) return -ENOENT; error = may_create(dir, new_dentry); if (error) return error; if (dir->i_sb != inode->i_sb) return -EXDEV; /* * A link to an append-only or immutable file cannot be created. */ if (IS_APPEND(inode) || IS_IMMUTABLE(inode)) return -EPERM; if (!dir->i_op->link) return -EPERM; if (S_ISDIR(inode->i_mode)) return -EPERM; error = security_inode_link(old_dentry, dir, new_dentry); if (error) return error; mutex_lock(&inode->i_mutex); /* Make sure we don't allow creating hardlink to an unlinked file */ if (inode->i_nlink == 0 && !(inode->i_state & I_LINKABLE)) error = -ENOENT; else if (max_links && inode->i_nlink >= max_links) error = -EMLINK; else { error = try_break_deleg(inode, delegated_inode); if (!error) error = dir->i_op->link(old_dentry, dir, new_dentry); } if (!error && (inode->i_state & I_LINKABLE)) { spin_lock(&inode->i_lock); inode->i_state &= ~I_LINKABLE; spin_unlock(&inode->i_lock); } mutex_unlock(&inode->i_mutex); if (!error) fsnotify_link(dir, inode, new_dentry); return error; } EXPORT_SYMBOL(vfs_link); /* * Hardlinks are often used in delicate situations. We avoid * security-related surprises by not following symlinks on the * newname. --KAB * * We don't follow them on the oldname either to be compatible * with linux 2.0, and to avoid hard-linking to directories * and other special files. --ADM */ SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname, int, newdfd, const char __user *, newname, int, flags) { struct dentry *new_dentry; struct path old_path, new_path; struct inode *delegated_inode = NULL; int how = 0; int error; if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0) return -EINVAL; /* * To use null names we require CAP_DAC_READ_SEARCH * This ensures that not everyone will be able to create * handlink using the passed filedescriptor. */ if (flags & AT_EMPTY_PATH) { if (!capable(CAP_DAC_READ_SEARCH)) return -ENOENT; how = LOOKUP_EMPTY; } if (flags & AT_SYMLINK_FOLLOW) how |= LOOKUP_FOLLOW; retry: error = user_path_at(olddfd, oldname, how, &old_path); if (error) return error; new_dentry = user_path_create(newdfd, newname, &new_path, (how & LOOKUP_REVAL)); error = PTR_ERR(new_dentry); if (IS_ERR(new_dentry)) goto out; error = -EXDEV; if (old_path.mnt != new_path.mnt) goto out_dput; error = may_linkat(&old_path); if (unlikely(error)) goto out_dput; error = security_path_link(old_path.dentry, &new_path, new_dentry); if (error) goto out_dput; error = vfs_link(old_path.dentry, new_path.dentry->d_inode, new_dentry, &delegated_inode); out_dput: done_path_create(&new_path, new_dentry); if (delegated_inode) { error = break_deleg_wait(&delegated_inode); if (!error) { path_put(&old_path); goto retry; } } if (retry_estale(error, how)) { path_put(&old_path); how |= LOOKUP_REVAL; goto retry; } out: path_put(&old_path); return error; } SYSCALL_DEFINE2(link, const char __user *, oldname, const char __user *, newname) { return sys_linkat(AT_FDCWD, oldname, AT_FDCWD, newname, 0); } /** * vfs_rename - rename a filesystem object * @old_dir: parent of source * @old_dentry: source * @new_dir: parent of destination * @new_dentry: destination * @delegated_inode: returns an inode needing a delegation break * @flags: rename flags * * The caller must hold multiple mutexes--see lock_rename()). * * If vfs_rename discovers a delegation in need of breaking at either * the source or destination, it will return -EWOULDBLOCK and return a * reference to the inode in delegated_inode. The caller should then * break the delegation and retry. Because breaking a delegation may * take a long time, the caller should drop all locks before doing * so. * * Alternatively, a caller may pass NULL for delegated_inode. This may * be appropriate for callers that expect the underlying filesystem not * to be NFS exported. * * The worst of all namespace operations - renaming directory. "Perverted" * doesn't even start to describe it. Somebody in UCB had a heck of a trip... * Problems: * a) we can get into loop creation. * b) race potential - two innocent renames can create a loop together. * That's where 4.4 screws up. Current fix: serialization on * sb->s_vfs_rename_mutex. We might be more accurate, but that's another * story. * c) we have to lock _four_ objects - parents and victim (if it exists), * and source (if it is not a directory). * And that - after we got ->i_mutex on parents (until then we don't know * whether the target exists). Solution: try to be smart with locking * order for inodes. We rely on the fact that tree topology may change * only under ->s_vfs_rename_mutex _and_ that parent of the object we * move will be locked. Thus we can rank directories by the tree * (ancestors first) and rank all non-directories after them. * That works since everybody except rename does "lock parent, lookup, * lock child" and rename is under ->s_vfs_rename_mutex. * HOWEVER, it relies on the assumption that any object with ->lookup() * has no more than 1 dentry. If "hybrid" objects will ever appear, * we'd better make sure that there's no link(2) for them. * d) conversion from fhandle to dentry may come in the wrong moment - when * we are removing the target. Solution: we will have to grab ->i_mutex * in the fhandle_to_dentry code. [FIXME - current nfsfh.c relies on * ->i_mutex on parents, which works but leads to some truly excessive * locking]. */ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry, struct inode *new_dir, struct dentry *new_dentry, struct inode **delegated_inode, unsigned int flags) { int error; bool is_dir = d_is_dir(old_dentry); const unsigned char *old_name; struct inode *source = old_dentry->d_inode; struct inode *target = new_dentry->d_inode; bool new_is_dir = false; unsigned max_links = new_dir->i_sb->s_max_links; if (source == target) return 0; error = may_delete(old_dir, old_dentry, is_dir); if (error) return error; if (!target) { error = may_create(new_dir, new_dentry); } else { new_is_dir = d_is_dir(new_dentry); if (!(flags & RENAME_EXCHANGE)) error = may_delete(new_dir, new_dentry, is_dir); else error = may_delete(new_dir, new_dentry, new_is_dir); } if (error) return error; if (!old_dir->i_op->rename && !old_dir->i_op->rename2) return -EPERM; if (flags && !old_dir->i_op->rename2) return -EINVAL; /* * If we are going to change the parent - check write permissions, * we'll need to flip '..'. */ if (new_dir != old_dir) { if (is_dir) { error = inode_permission(source, MAY_WRITE); if (error) return error; } if ((flags & RENAME_EXCHANGE) && new_is_dir) { error = inode_permission(target, MAY_WRITE); if (error) return error; } } error = security_inode_rename(old_dir, old_dentry, new_dir, new_dentry, flags); if (error) return error; old_name = fsnotify_oldname_init(old_dentry->d_name.name); dget(new_dentry); if (!is_dir || (flags & RENAME_EXCHANGE)) lock_two_nondirectories(source, target); else if (target) mutex_lock(&target->i_mutex); error = -EBUSY; if (is_local_mountpoint(old_dentry) || is_local_mountpoint(new_dentry)) goto out; if (max_links && new_dir != old_dir) { error = -EMLINK; if (is_dir && !new_is_dir && new_dir->i_nlink >= max_links) goto out; if ((flags & RENAME_EXCHANGE) && !is_dir && new_is_dir && old_dir->i_nlink >= max_links) goto out; } if (is_dir && !(flags & RENAME_EXCHANGE) && target) shrink_dcache_parent(new_dentry); if (!is_dir) { error = try_break_deleg(source, delegated_inode); if (error) goto out; } if (target && !new_is_dir) { error = try_break_deleg(target, delegated_inode); if (error) goto out; } if (!old_dir->i_op->rename2) { error = old_dir->i_op->rename(old_dir, old_dentry, new_dir, new_dentry); } else { WARN_ON(old_dir->i_op->rename != NULL); error = old_dir->i_op->rename2(old_dir, old_dentry, new_dir, new_dentry, flags); } if (error) goto out; if (!(flags & RENAME_EXCHANGE) && target) { if (is_dir) target->i_flags |= S_DEAD; dont_mount(new_dentry); detach_mounts(new_dentry); } if (!(old_dir->i_sb->s_type->fs_flags & FS_RENAME_DOES_D_MOVE)) { if (!(flags & RENAME_EXCHANGE)) d_move(old_dentry, new_dentry); else d_exchange(old_dentry, new_dentry); } out: if (!is_dir || (flags & RENAME_EXCHANGE)) unlock_two_nondirectories(source, target); else if (target) mutex_unlock(&target->i_mutex); dput(new_dentry); if (!error) { fsnotify_move(old_dir, new_dir, old_name, is_dir, !(flags & RENAME_EXCHANGE) ? target : NULL, old_dentry); if (flags & RENAME_EXCHANGE) { fsnotify_move(new_dir, old_dir, old_dentry->d_name.name, new_is_dir, NULL, new_dentry); } } fsnotify_oldname_free(old_name); return error; } EXPORT_SYMBOL(vfs_rename); SYSCALL_DEFINE5(renameat2, int, olddfd, const char __user *, oldname, int, newdfd, const char __user *, newname, unsigned int, flags) { struct dentry *old_dir, *new_dir; struct dentry *old_dentry, *new_dentry; struct dentry *trap; struct nameidata oldnd, newnd; struct inode *delegated_inode = NULL; struct filename *from; struct filename *to; unsigned int lookup_flags = 0; bool should_retry = false; int error; if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE | RENAME_WHITEOUT)) return -EINVAL; if ((flags & (RENAME_NOREPLACE | RENAME_WHITEOUT)) && (flags & RENAME_EXCHANGE)) return -EINVAL; if ((flags & RENAME_WHITEOUT) && !capable(CAP_MKNOD)) return -EPERM; retry: from = user_path_parent(olddfd, oldname, &oldnd, lookup_flags); if (IS_ERR(from)) { error = PTR_ERR(from); goto exit; } to = user_path_parent(newdfd, newname, &newnd, lookup_flags); if (IS_ERR(to)) { error = PTR_ERR(to); goto exit1; } error = -EXDEV; if (oldnd.path.mnt != newnd.path.mnt) goto exit2; old_dir = oldnd.path.dentry; error = -EBUSY; if (oldnd.last_type != LAST_NORM) goto exit2; new_dir = newnd.path.dentry; if (flags & RENAME_NOREPLACE) error = -EEXIST; if (newnd.last_type != LAST_NORM) goto exit2; error = mnt_want_write(oldnd.path.mnt); if (error) goto exit2; oldnd.flags &= ~LOOKUP_PARENT; newnd.flags &= ~LOOKUP_PARENT; if (!(flags & RENAME_EXCHANGE)) newnd.flags |= LOOKUP_RENAME_TARGET; retry_deleg: trap = lock_rename(new_dir, old_dir); old_dentry = lookup_hash(&oldnd); error = PTR_ERR(old_dentry); if (IS_ERR(old_dentry)) goto exit3; /* source must exist */ error = -ENOENT; if (d_is_negative(old_dentry)) goto exit4; new_dentry = lookup_hash(&newnd); error = PTR_ERR(new_dentry); if (IS_ERR(new_dentry)) goto exit4; error = -EEXIST; if ((flags & RENAME_NOREPLACE) && d_is_positive(new_dentry)) goto exit5; if (flags & RENAME_EXCHANGE) { error = -ENOENT; if (d_is_negative(new_dentry)) goto exit5; if (!d_is_dir(new_dentry)) { error = -ENOTDIR; if (newnd.last.name[newnd.last.len]) goto exit5; } } /* unless the source is a directory trailing slashes give -ENOTDIR */ if (!d_is_dir(old_dentry)) { error = -ENOTDIR; if (oldnd.last.name[oldnd.last.len]) goto exit5; if (!(flags & RENAME_EXCHANGE) && newnd.last.name[newnd.last.len]) goto exit5; } /* source should not be ancestor of target */ error = -EINVAL; if (old_dentry == trap) goto exit5; /* target should not be an ancestor of source */ if (!(flags & RENAME_EXCHANGE)) error = -ENOTEMPTY; if (new_dentry == trap) goto exit5; error = security_path_rename(&oldnd.path, old_dentry, &newnd.path, new_dentry, flags); if (error) goto exit5; error = vfs_rename(old_dir->d_inode, old_dentry, new_dir->d_inode, new_dentry, &delegated_inode, flags); exit5: dput(new_dentry); exit4: dput(old_dentry); exit3: unlock_rename(new_dir, old_dir); if (delegated_inode) { error = break_deleg_wait(&delegated_inode); if (!error) goto retry_deleg; } mnt_drop_write(oldnd.path.mnt); exit2: if (retry_estale(error, lookup_flags)) should_retry = true; path_put(&newnd.path); putname(to); exit1: path_put(&oldnd.path); putname(from); if (should_retry) { should_retry = false; lookup_flags |= LOOKUP_REVAL; goto retry; } exit: return error; } SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname, int, newdfd, const char __user *, newname) { return sys_renameat2(olddfd, oldname, newdfd, newname, 0); } SYSCALL_DEFINE2(rename, const char __user *, oldname, const char __user *, newname) { return sys_renameat2(AT_FDCWD, oldname, AT_FDCWD, newname, 0); } int vfs_whiteout(struct inode *dir, struct dentry *dentry) { int error = may_create(dir, dentry); if (error) return error; if (!dir->i_op->mknod) return -EPERM; return dir->i_op->mknod(dir, dentry, S_IFCHR | WHITEOUT_MODE, WHITEOUT_DEV); } EXPORT_SYMBOL(vfs_whiteout); int readlink_copy(char __user *buffer, int buflen, const char *link) { int len = PTR_ERR(link); if (IS_ERR(link)) goto out; len = strlen(link); if (len > (unsigned) buflen) len = buflen; if (copy_to_user(buffer, link, len)) len = -EFAULT; out: return len; } EXPORT_SYMBOL(readlink_copy); /* * A helper for ->readlink(). This should be used *ONLY* for symlinks that * have ->follow_link() touching nd only in nd_set_link(). Using (or not * using) it for any given inode is up to filesystem. */ int generic_readlink(struct dentry *dentry, char __user *buffer, int buflen) { struct nameidata nd; void *cookie; int res; nd.depth = 0; cookie = dentry->d_inode->i_op->follow_link(dentry, &nd); if (IS_ERR(cookie)) return PTR_ERR(cookie); res = readlink_copy(buffer, buflen, nd_get_link(&nd)); if (dentry->d_inode->i_op->put_link) dentry->d_inode->i_op->put_link(dentry, &nd, cookie); return res; } EXPORT_SYMBOL(generic_readlink); /* get the link contents into pagecache */ static char *page_getlink(struct dentry * dentry, struct page **ppage) { char *kaddr; struct page *page; struct address_space *mapping = dentry->d_inode->i_mapping; page = read_mapping_page(mapping, 0, NULL); if (IS_ERR(page)) return (char*)page; *ppage = page; kaddr = kmap(page); nd_terminate_link(kaddr, dentry->d_inode->i_size, PAGE_SIZE - 1); return kaddr; } int page_readlink(struct dentry *dentry, char __user *buffer, int buflen) { struct page *page = NULL; int res = readlink_copy(buffer, buflen, page_getlink(dentry, &page)); if (page) { kunmap(page); page_cache_release(page); } return res; } EXPORT_SYMBOL(page_readlink); void *page_follow_link_light(struct dentry *dentry, struct nameidata *nd) { struct page *page = NULL; nd_set_link(nd, page_getlink(dentry, &page)); return page; } EXPORT_SYMBOL(page_follow_link_light); void page_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie) { struct page *page = cookie; if (page) { kunmap(page); page_cache_release(page); } } EXPORT_SYMBOL(page_put_link); /* * The nofs argument instructs pagecache_write_begin to pass AOP_FLAG_NOFS */ int __page_symlink(struct inode *inode, const char *symname, int len, int nofs) { struct address_space *mapping = inode->i_mapping; struct page *page; void *fsdata; int err; char *kaddr; unsigned int flags = AOP_FLAG_UNINTERRUPTIBLE; if (nofs) flags |= AOP_FLAG_NOFS; retry: err = pagecache_write_begin(NULL, mapping, 0, len-1, flags, &page, &fsdata); if (err) goto fail; kaddr = kmap_atomic(page); memcpy(kaddr, symname, len-1); kunmap_atomic(kaddr); err = pagecache_write_end(NULL, mapping, 0, len-1, len-1, page, fsdata); if (err < 0) goto fail; if (err < len-1) goto retry; mark_inode_dirty(inode); return 0; fail: return err; } EXPORT_SYMBOL(__page_symlink); int page_symlink(struct inode *inode, const char *symname, int len) { return __page_symlink(inode, symname, len, !(mapping_gfp_mask(inode->i_mapping) & __GFP_FS)); } EXPORT_SYMBOL(page_symlink); const struct inode_operations page_symlink_inode_operations = { .readlink = generic_readlink, .follow_link = page_follow_link_light, .put_link = page_put_link, }; EXPORT_SYMBOL(page_symlink_inode_operations);