From: Al Viro Date: Wed, 8 Jun 2016 01:26:55 +0000 (-0400) Subject: fix d_walk()/non-delayed __d_free() race X-Git-Tag: v4.4.14-KARO~34 X-Git-Url: https://git.karo-electronics.de/?p=karo-tx-linux.git;a=commitdiff_plain;h=2b11d80e1aa70b56c6431e4dc3c686ffc61a73bf fix d_walk()/non-delayed __d_free() race commit 3d56c25e3bb0726a5c5e16fc2d9e38f8ed763085 upstream. Ascend-to-parent logics in d_walk() depends on all encountered child dentries not getting freed without an RCU delay. Unfortunately, in quite a few cases it is not true, with hard-to-hit oopsable race as the result. Fortunately, the fix is simiple; right now the rule is "if it ever been hashed, freeing must be delayed" and changing it to "if it ever had a parent, freeing must be delayed" closes that hole and covers all cases the old rule used to cover. Moreover, pipes and sockets remain _not_ covered, so we do not introduce RCU delay in the cases which are the reason for having that delay conditional in the first place. Signed-off-by: Al Viro Signed-off-by: Greg Kroah-Hartman --- diff --git a/fs/dcache.c b/fs/dcache.c index 18effa378f97..108d7d810be3 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1618,7 +1618,7 @@ struct dentry *d_alloc(struct dentry * parent, const struct qstr *name) struct dentry *dentry = __d_alloc(parent->d_sb, name); if (!dentry) return NULL; - + dentry->d_flags |= DCACHE_RCUACCESS; spin_lock(&parent->d_lock); /* * don't need child lock because it is not subject @@ -2413,7 +2413,6 @@ static void __d_rehash(struct dentry * entry, struct hlist_bl_head *b) { BUG_ON(!d_unhashed(entry)); hlist_bl_lock(b); - entry->d_flags |= DCACHE_RCUACCESS; hlist_bl_add_head_rcu(&entry->d_hash, b); hlist_bl_unlock(b); } @@ -2632,6 +2631,7 @@ static void __d_move(struct dentry *dentry, struct dentry *target, /* ... and switch them in the tree */ if (IS_ROOT(dentry)) { /* splicing a tree */ + dentry->d_flags |= DCACHE_RCUACCESS; dentry->d_parent = target->d_parent; target->d_parent = target; list_del_init(&target->d_child);