From 3cab989afd8d8d1bc3d99fef0e7ed87c31e7b647 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Fri, 24 Apr 2015 15:47:07 -0400 Subject: 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: Al Viro --- fs/namei.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index ffab2e06e147..4a8d998b7274 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -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; } -- cgit v1.2.3-59-g8ed1b