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Commit 3cab989a authored by Al Viro's avatar Al Viro
Browse files

RCU pathwalk breakage when running into a symlink overmounting something 



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().

Cc: stable@vger.kernel.org # since 2.6.39
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent ac74d8d6

fs/namei.c

+4 −2
Original line number Diff line number Diff line
@@ -1590,7 +1590,8 @@ static inline int walk_component(struct nameidata *nd, struct path *path, 


	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;

			}
@@ -3045,7 +3046,8 @@ static int do_last(struct nameidata *nd, struct path *path, 


	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;

			}