| From 204179f43e2f26e5e2ff459f3b089f60d755d08d Mon Sep 17 00:00:00 2001 |
| From: Michel Machado <michel@digirati.com.br> |
| Date: Tue, 21 Feb 2012 11:04:13 +0000 |
| Subject: neighbour: Fixed race condition at tbl->nht |
| |
| |
| From: Michel Machado <michel@digirati.com.br> |
| |
| [ 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 <michel@digirati.com.br> |
| CC: "David S. Miller" <davem@davemloft.net> |
| CC: Eric Dumazet <eric.dumazet@gmail.com> |
| Signed-off-by: David S. Miller <davem@davemloft.net> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| 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 |