[lkml]   [2012]   [Mar]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[ 16/38] neighbour: Fixed race condition at tbl->nht
3.0-stable review patch.  If anyone has any objections, please let me know.


From: Michel Machado <>

[ 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 <>
CC: "David S. Miller" <>
CC: Eric Dumazet <>
Signed-off-by: David S. Miller <>
Signed-off-by: Greg Kroah-Hartman <>
net/core/neighbour.c | 2 ++
1 file changed, 2 insertions(+)

--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -823,6 +823,8 @@ next_elt:
+ 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

 \ /
  Last update: 2012-03-17 00:59    [W:0.173 / U:3.968 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site