RCU pathwalk breakage when running into a symlink overmounting something (3cab989a) · Commits · 戴 / test

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:

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

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 @@ 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;
		}

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