From: Michel Machado Date: Tue, 21 Feb 2012 11:04:13 +0000 (+0000) Subject: neighbour: Fixed race condition at tbl->nht X-Git-Tag: v3.2.12~27 X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=983af6e10958557843e4b5546c96e371ee3c8ddd;p=karo-tx-linux.git neighbour: Fixed race condition at tbl->nht [ 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 --- diff --git a/net/core/neighbour.c b/net/core/neighbour.c index 5ac07d31fbc9..7aafaeddfcbf 100644 --- 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