1 files changed, 68 insertions, 33 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 2e4356f..a85b073 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -74,6 +74,16 @@
 #include <linux/poll.h>
 #include "internal.h"
 
+/* NOTE:
+ *	Implementing inode permission operations in /proc is almost
+ *	certainly an error.  Permission checks need to happen during
+ *	each system call not at open time.  The reason is that most of
+ *	what we wish to check for permissions in /proc varies at runtime.
+ *
+ *	The classic example of a problem is opening file descriptors
+ *	in /proc for a task before it execs a suid executable.
+ */
+
 /*
  * For hysterical raisins we keep the same inumbers as in the old procfs.
  * Feel free to change the macro below - just keep the range distinct from
@@ -494,13 +504,11 @@ static int proc_oom_score(struct task_struct *task, char *buffer)
 
 /* If the process being read is separated by chroot from the reading process,
  * don't let the reader access the threads.
- *
- * note: this does dput(root) and mntput(vfsmnt) on exit.
  */
-static int proc_check_chroot(struct dentry *root, struct vfsmount *vfsmnt)
+static int proc_check_chroot(struct dentry *de, struct vfsmount *mnt)
 {
-	struct dentry *de, *base;
-	struct vfsmount *our_vfsmnt, *mnt;
+	struct dentry *base;
+	struct vfsmount *our_vfsmnt;
 	int res = 0;
 
 	read_lock(&current->fs->lock);
@@ -509,8 +517,6 @@ static int proc_check_chroot(struct dentry *root, struct vfsmount *vfsmnt)
 	read_unlock(&current->fs->lock);
 
 	spin_lock(&vfsmount_lock);
-	de = root;
-	mnt = vfsmnt;
 
 	while (mnt != our_vfsmnt) {
 		if (mnt == mnt->mnt_parent)
@@ -526,8 +532,6 @@ static int proc_check_chroot(struct dentry *root, struct vfsmount *vfsmnt)
 exit:
 	dput(base);
 	mntput(our_vfsmnt);
-	dput(root);
-	mntput(vfsmnt);
 	return res;
 out:
 	spin_unlock(&vfsmount_lock);
@@ -535,23 +539,6 @@ out:
 	goto exit;
 }
 
-static int proc_check_root(struct inode *inode)
-{
-	struct dentry *root;
-	struct vfsmount *vfsmnt;
-
-	if (proc_root_link(inode, &root, &vfsmnt)) /* Ewww... */
-		return -ENOENT;
-	return proc_check_chroot(root, vfsmnt);
-}
-
-static int proc_permission(struct inode *inode, int mask, struct nameidata *nd)
-{
-	if (generic_permission(inode, mask, NULL) != 0)
-		return -EACCES;
-	return proc_check_root(inode);
-}
-
 extern struct seq_operations proc_pid_maps_op;
 static int maps_open(struct inode *inode, struct file *file)
 {
@@ -1048,6 +1035,48 @@ static struct file_operations proc_seccomp_operations = {
 };
 #endif /* CONFIG_SECCOMP */
 
+static int proc_check_dentry_visible(struct inode *inode,
+	struct dentry *dentry, struct vfsmount *mnt)
+{
+	/* Verify that the current process can already see the
+	 * file pointed at by the file descriptor.
+	 * This prevents /proc from being an accidental information leak.
+	 *
+	 * This prevents access to files that are not visible do to
+	 * being on the otherside of a chroot, in a different
+	 * namespace, or are simply process local (like pipes).
+	 */
+	struct task_struct *task;
+	struct files_struct *task_files, *files;
+	int error = -EACCES;
+
+	/* See if the the two tasks share a commone set of
+	 * file descriptors.  If so everything is visible.
+	 */
+	task = proc_task(inode);
+	if (!task)
+		goto out;
+	files = get_files_struct(current);
+	task_files = get_files_struct(task);
+	if (files && task_files && (files == task_files))
+		error = 0;
+	if (task_files)
+		put_files_struct(task_files);
+	if (files)
+		put_files_struct(files);
+	if (!error)
+		goto out;
+
+	/* If the two tasks don't share a common set of file
+	 * descriptors see if the destination dentry is already
+	 * visible in the current tasks filesystem namespace.
+	 */
+	error = proc_check_chroot(dentry, mnt);
+out:
+	return error;
+
+}
+
 static void *proc_pid_follow_link(struct dentry *dentry, struct nameidata *nd)
 {
 	struct inode *inode = dentry->d_inode;
@@ -1058,12 +1087,16 @@ static void *proc_pid_follow_link(struct dentry *dentry, struct nameidata *nd)
 
 	if (current->fsuid != inode->i_uid && !capable(CAP_DAC_OVERRIDE))
 		goto out;
-	error = proc_check_root(inode);
-	if (error)
-		goto out;
 
 	error = PROC_I(inode)->op.proc_get_link(inode, &nd->dentry, &nd->mnt);
 	nd->last_type = LAST_BIND;
+	if (error)
+		goto out;
+
+	/* Only return files this task can already see */
+	error = proc_check_dentry_visible(inode, nd->dentry, nd->mnt);
+	if (error)
+		path_release(nd);
 out:
 	return ERR_PTR(error);
 }
@@ -1104,15 +1137,18 @@ static int proc_pid_readlink(struct dentry * dentry, char __user * buffer, int b
 
 	if (current->fsuid != inode->i_uid && !capable(CAP_DAC_OVERRIDE))
 		goto out;
-	error = proc_check_root(inode);
-	if (error)
-		goto out;
 
 	error = PROC_I(inode)->op.proc_get_link(inode, &de, &mnt);
 	if (error)
 		goto out;
 
+	/* Only return files this task can already see */
+	error = proc_check_dentry_visible(inode, de, mnt);
+	if (error)
+		goto out_put;
+
 	error = do_proc_readlink(de, mnt, buffer, buflen);
+out_put:
 	dput(de);
 	mntput(mnt);
 out:
@@ -1512,7 +1548,6 @@ static struct file_operations proc_task_operations = {
  */
 static struct inode_operations proc_fd_inode_operations = {
 	.lookup		= proc_lookupfd,
-	.permission	= proc_permission,
 };
 
 static struct inode_operations proc_task_inode_operations = {