From 80279158472a5e10191c8f16a32af884dd16e803 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Fri, 23 Feb 2018 20:47:17 -0500 Subject: [PATCH] lock_parent() needs to recheck if dentry got __dentry_kill'ed under it commit 3b821409632ab778d46e807516b457dfa72736ed upstream. In case when dentry passed to lock_parent() is protected from freeing only by the fact that it's on a shrink list and trylock of parent fails, we could get hit by __dentry_kill() (and subsequent dentry_kill(parent)) between unlocking dentry and locking presumed parent. We need to recheck that dentry is alive once we lock both it and parent *and* postpone rcu_read_unlock() until after that point. Otherwise we could return a pointer to struct dentry that already is rcu-scheduled for freeing, with ->d_lock held on it; caller's subsequent attempt to unlock it can end up with memory corruption. Signed-off-by: Al Viro Signed-off-by: Ben Hutchings --- fs/dcache.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index 8a84b99ea8d4..e1380da5c183 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -590,11 +590,16 @@ static inline struct dentry *lock_parent(struct dentry *dentry) spin_unlock(&parent->d_lock); goto again; } - rcu_read_unlock(); - if (parent != dentry) + if (parent != dentry) { spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED); - else + if (unlikely(dentry->d_lockref.count < 0)) { + spin_unlock(&parent->d_lock); + parent = NULL; + } + } else { parent = NULL; + } + rcu_read_unlock(); return parent; }