From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-Id: <20120316233811.948247688@linuxfoundation.org> Date: Fri, 16 Mar 2012 16:38:25 -0700 From: Greg KH To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Michel Machado , "David S. Miller" , Eric Dumazet Subject: [ 15/41] neighbour: Fixed race condition at tbl->nht In-Reply-To: <20120316233829.GA14022@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Michel Machado [ Upstream commit 84338a6c9dbb6ff3de4749864020f8f25d86fc81 ] When the fixed race condition happens: 1. While function neigh_periodic_work scans the neighbor hash table pointed by field tbl->nht, it unlocks and locks tbl->lock between buckets in order to call cond_resched. 2. Assume that function neigh_periodic_work calls cond_resched, that is, the lock tbl->lock is available, and function neigh_hash_grow runs. 3. Once function neigh_hash_grow finishes, and RCU calls neigh_hash_free_rcu, the original struct neigh_hash_table that function neigh_periodic_work was using doesn't exist anymore. 4. Once back at neigh_periodic_work, whenever the old struct neigh_hash_table is accessed, things can go badly. Signed-off-by: Michel Machado CC: "David S. Miller" CC: Eric Dumazet Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/core/neighbour.c | 2 ++ 1 file changed, 2 insertions(+) --- a/net/core/neighbour.c +++ b/net/core/neighbour.c @@ -802,6 +802,8 @@ next_elt: write_unlock_bh(&tbl->lock); cond_resched(); write_lock_bh(&tbl->lock); + nht = rcu_dereference_protected(tbl->nht, + lockdep_is_held(&tbl->lock)); } /* Cycle through all hash buckets every base_reachable_time/2 ticks. * ARP entry timeouts range from 1/2 base_reachable_time to 3/2