Patch "RCU pathwalk breakage when running into a symlink overmounting something" has been added to the 3.10-stable tree

This is a note to let you know that I've just added the patch titled

RCU pathwalk breakage when running into a symlink overmounting something

to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
rcu-pathwalk-breakage-when-running-into-a-symlink-overmounting-something.patch
and it can be found in the queue-3.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Al Viro <[email protected]>
Date: Fri, 24 Apr 2015 15:47:07 -0400
Subject: RCU pathwalk breakage when running into a symlink overmounting something

From: Al Viro <[email protected]>

commit 3cab989afd8d8d1bc3d99fef0e7ed87c31e7b647 upstream.

Calling unlazy_walk() in walk_component() and do_last() when we find a symlink that needs to be followed doesn't acquire a reference to vfsmount. That's fine when the symlink is on the same vfsmount as the parent directory (which is almost always the case), but it's not always true - one _can_ manage to bind a symlink on top of something. And in such cases we end up with excessive mntput().

---
 fs/namei.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

@@ -1542,7 +1542,8 @@ static inline int walk_component(struct
 
 	if (should_follow_link(inode, follow)) {
 		if (nd->flags & LOOKUP_RCU) {
-			if (unlikely(unlazy_walk(nd, path->dentry))) {
+			if (unlikely(nd->path.mnt != path->mnt ||
+				     unlazy_walk(nd, path->dentry))) {
 				err = -ECHILD;
 				goto out_err;
 			}

@@ -2824,7 +2825,8 @@ finish_lookup:
 
 	if (should_follow_link(inode, !symlink_ok)) {
 		if (nd->flags & LOOKUP_RCU) {
-			if (unlikely(unlazy_walk(nd, path->dentry))) {
+			if (unlikely(nd->path.mnt != path->mnt ||
+				     unlazy_walk(nd, path->dentry))) {
 				error = -ECHILD;
 				goto out;
 			}

Patches currently in stable-queue which might be from [email protected] are

queue-3.10/fs-binfmt_elf.c-fix-bug-in-loading-of-pie-binaries.patch queue-3.10/rcu-pathwalk-breakage-when-running-into-a-symlink-overmounting-something.patch