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RCU pathwalk breakage when running into a symlink overmounting something

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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>
This commit is contained in:
Al Viro 2015-04-24 15:47:07 -04:00 committed by Greg Kroah-Hartman
parent 10e3015263
commit 3b388f33a1
1 changed files with 4 additions and 2 deletions
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6
fs/namei.c
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@ -1542,7 +1542,8 @@ 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))) {
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;
}