From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965449AbcHNLcH (ORCPT ); Sun, 14 Aug 2016 07:32:07 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:52391 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964811AbcHNLcE (ORCPT ); Sun, 14 Aug 2016 07:32:04 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Al Viro" Date: Sat, 13 Aug 2016 18:42:51 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 156/305] fix d_walk()/non-delayed __d_free() race In-Reply-To: X-SA-Exim-Connect-IP: 92.40.249.202 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.37-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Al Viro 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 [bwh: Backported to 3.16: - Adjust context - Also set the flag in __d_materialise_dentry())] Signed-off-by: Ben Hutchings --- fs/dcache.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1502,7 +1502,7 @@ struct dentry *d_alloc(struct dentry * p 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 @@ -2354,7 +2354,6 @@ static void __d_rehash(struct dentry * e { 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); } @@ -2560,6 +2559,7 @@ static void __d_move(struct dentry *dent /* ... and switch the parents */ if (IS_ROOT(dentry)) { + dentry->d_flags |= DCACHE_RCUACCESS; dentry->d_parent = target->d_parent; target->d_parent = target; INIT_LIST_HEAD(&target->d_child); @@ -2696,6 +2696,7 @@ static void __d_materialise_dentry(struc switch_names(dentry, anon, false); + dentry->d_flags |= DCACHE_RCUACCESS; dentry->d_parent = dentry; list_del_init(&dentry->d_child); anon->d_parent = dparent;