From: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Date: Thu, 12 Jun 2014 00:29:13 -0400 Subject: [PATCH] lock_parent: don't step on stale ->d_parent of all-but-freed one Commit c2338f2dc7c1e9f6202f370c64ffd7f44f3d4b51 upstream. Dentry that had been through (or into) __dentry_kill() might be seen by shrink_dentry_list(); that's normal, it'll be taken off the shrink list and freed if __dentry_kill() has already finished. The problem is, its ->d_parent might be pointing to already freed dentry, so lock_parent() needs to be careful. We need to check that dentry hasn't already gone into __dentry_kill() *and* grab rcu_read_lock() before dropping ->d_lock - the latter makes sure that whatever we see in ->d_parent after dropping ->d_lock it won't be freed until we drop rcu_read_lock(). Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx # v3.15 Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> --- Al forgot to mark this for stable in the commit, so I'm mailing it in explicitly. fs/dcache.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/fs/dcache.c b/fs/dcache.c index be2bea834bf4..e99c6f529ba8 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -532,10 +532,12 @@ static inline struct dentry *lock_parent(struct dentry *dentry) struct dentry *parent = dentry->d_parent; if (IS_ROOT(dentry)) return NULL; + if (unlikely((int)dentry->d_lockref.count < 0)) + return NULL; if (likely(spin_trylock(&parent->d_lock))) return parent; - spin_unlock(&dentry->d_lock); rcu_read_lock(); + spin_unlock(&dentry->d_lock); again: parent = ACCESS_ONCE(dentry->d_parent); spin_lock(&parent->d_lock); -- 2.0.0.240.g622b917 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html