Messages in this thread Patch in this message | | | Date | Fri, 16 Mar 2012 16:38:25 -0700 | From | Greg KH <> | Subject | [ 15/41] neighbour: Fixed race condition at tbl->nht |
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3.2-stable review patch. If anyone has any objections, please let me know.
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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
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