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neighbour: Fixed race condition at tbl->nht

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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>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Michel Machado 2012-02-21 16:04:13 -05:00 committed by David S. Miller
parent 3d8f93083b
commit 84338a6c9d
1 changed files with 2 additions and 0 deletions
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2
net/core/neighbour.c
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@ -826,6 +826,8 @@ static void neigh_periodic_work(struct work_struct *work)
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