[PATCH 3.4 055/146] RCU pathwalk breakage when running into a symlink overmounting something

lizf
2015-09-15T09:44:45Z

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

3.4.109-rc1 review patch. If anyone has any objections, please let me know.

------------------

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>
[lizf: Backported to 3.4: drop the changes to do_last()]
Signed-off-by: Zefan Li <lizefan@huawei.com>
---
fs/namei.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/namei.c b/fs/namei.c
index bdcd705..9c4b9b8 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1314,7 +1314,8 @@ static inline int walk_component(struct nameidata *nd, struct path *path,
}
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))) {
terminate_walk(nd);
return -ECHILD;
}
--
1.9.1