Patch "RCU pathwalk breakage when running into a symlink overmounting something" has been added to the 4.0-stable tree

Patch "RCU pathwalk breakage when running into a symlink overmounting something" has been added to the 4.0-stable tree

[gregkh]

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 4.0-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-4.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 3cab989afd8d8d1bc3d99fef0e7ed87c31e7b647 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Fri, 24 Apr 2015 15:47:07 -0400
Subject: RCU pathwalk breakage when running into a symlink overmounting something

From: Al Viro <viro@zeniv.linux.org.uk>

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().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1591,7 +1591,8 @@ static inline int walk_component(struct
 
 	if (should_follow_link(path->dentry, 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;
 			}
@@ -3047,7 +3048,8 @@ finish_lookup:
 
 	if (should_follow_link(path->dentry, !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 viro@zeniv.linux.org.uk are

queue-4.0/fs-binfmt_elf.c-fix-bug-in-loading-of-pie-binaries.patch
queue-4.0/rcu-pathwalk-breakage-when-running-into-a-symlink-overmounting-something.patch
queue-4.0/nfs-fix-bug-crash-in-notify_change-with-patch-to-chown_common.patch