From a26f33c50cb736da55437cef761d48d72fe89d3e Mon Sep 17 00:00:00 2001 From: Al Viro Date: Fri, 24 Apr 2015 15:47:07 -0400 Subject: [PATCH] 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 [lizf: Backported to 3.4: drop the changes to do_last()] Signed-off-by: Zefan Li --- fs/namei.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/namei.c b/fs/namei.c index bdcd70544fcea..9c4b9b811d7b1 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; } -- 2.47.2