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Date: Fri, 16 Mar 2012 16:38:25 -0700 From: Greg KH <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org, stable@...r.kernel.org Cc: torvalds@...ux-foundation.org, akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk, Michel Machado <michel@...irati.com.br>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <eric.dumazet@...il.com> Subject: [ 15/41] neighbour: Fixed race condition at tbl->nht 3.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Michel Machado <michel@...irati.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@...irati.com.br> CC: "David S. Miller" <davem@...emloft.net> CC: Eric Dumazet <eric.dumazet@...il.com> Signed-off-by: David S. Miller <davem@...emloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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