From 84338a6c9dbb6ff3de4749864020f8f25d86fc81 Mon Sep 17 00:00:00 2001 From: Michel Machado Date: Tue, 21 Feb 2012 16:04:13 -0500 Subject: [PATCH] neighbour: Fixed race condition at tbl->nht 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 Acked-by: Eric Dumazet Signed-off-by: David S. Miller --- net/core/neighbour.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/net/core/neighbour.c b/net/core/neighbour.c index e287346e093..2a83914b027 100644 --- a/net/core/neighbour.c +++ b/net/core/neighbour.c @@ -826,6 +826,8 @@ 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 -- 2.20.1