RCU pathwalk breakage when running into a symlink overmounting something
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>
diff --git a/fs/namei.c b/fs/namei.c
index 0dd72c8..ccb8000 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1545,7 +1545,8 @@
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;
}
@@ -2992,7 +2993,8 @@
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;
}