| From | Luis Henriques <> | Subject | [PATCH 3.16.y-ckt 146/180] RCU pathwalk breakage when running into a symlink overmounting something | Date | Thu, 7 May 2015 10:45:55 +0100 |
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3.16.7-ckt11 -stable review patch. If anyone has any objections, please let me know.
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From: Al Viro <viro@zeniv.linux.org.uk>
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: Luis Henriques <luis.henriques@canonical.com> --- fs/namei.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c index 0b79fe47502a..19ac9c89dbab 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1554,7 +1554,8 @@ 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; } @@ -3015,7 +3016,8 @@ 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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