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-rw-r--r--fs/namei.c72
1 files changed, 70 insertions, 2 deletions
diff --git a/fs/namei.c b/fs/namei.c
index 16109da..9d3033d 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -960,6 +960,7 @@ static int follow_automount(struct path *path, unsigned flags,
/*
* Handle a dentry that is managed in some way.
+ * - Flagged for transit management (autofs)
* - Flagged as mountpoint
* - Flagged as automount point
*
@@ -979,6 +980,16 @@ static int follow_managed(struct path *path, unsigned flags)
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)
+ return ret == -EISDIR ? 0 : ret;
+ }
+
/* Transit to a mounted filesystem. */
if (managed & DCACHE_MOUNTED) {
struct vfsmount *mounted = lookup_mnt(path);
@@ -1012,7 +1023,7 @@ static int follow_managed(struct path *path, unsigned flags)
return 0;
}
-int follow_down(struct path *path)
+int follow_down_one(struct path *path)
{
struct vfsmount *mounted;
@@ -1029,14 +1040,19 @@ int follow_down(struct path *path)
/*
* Skip to top of mountpoint pile in rcuwalk mode. We abort the rcu-walk if we
- * meet an automount point and we're not walking to "..". True is returned to
+ * meet a managed dentry and we're not walking to "..". True is returned to
* continue, false to abort.
*/
static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
struct inode **inode, bool reverse_transit)
{
+ unsigned abort_mask =
+ reverse_transit ? 0 : DCACHE_MANAGE_TRANSIT;
+
while (d_mountpoint(path->dentry)) {
struct vfsmount *mounted;
+ if (path->dentry->d_flags & abort_mask)
+ return true;
mounted = __lookup_mnt(path->mnt, path->dentry, 1);
if (!mounted)
break;
@@ -1087,6 +1103,57 @@ static int follow_dotdot_rcu(struct nameidata *nd)
}
/*
+ * 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.
+ *
+ * Care must be taken as namespace_sem may be held (indicated by mounting_here
+ * being true).
+ */
+int follow_down(struct path *path, bool mounting_here)
+{
+ 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, mounting_here);
+ 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;
+}
+
+/*
* Skip to top of mountpoint pile in refwalk mode for follow_dotdot()
*/
static void follow_mount(struct path *path)
@@ -3530,6 +3597,7 @@ const struct inode_operations page_symlink_inode_operations = {
};
EXPORT_SYMBOL(user_path_at);
+EXPORT_SYMBOL(follow_down_one);
EXPORT_SYMBOL(follow_down);
EXPORT_SYMBOL(follow_up);
EXPORT_SYMBOL(get_write_access); /* binfmt_aout */
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