Re: boot crash in arp_error_report() (Re: [GIT] Networking)

[Eric Dumazet <eric.dumazet@gmail.com>]

Le jeudi 27 mai 2010 à 21:47 +0200, Eric Dumazet a écrit :

> I am looking at this bug report, as I am probably at fault, please give
> me one or two hour ;)

I believe problem comes from commit 7fee226ad2
(net: add a noref bit on skb dst)

We probably should add a WARN in __skb_queue_tail() and similar enqueue
 functions to catch other problems. I'll post a followup.

Thanks !

[PATCH] net: fix __neigh_event_send()

commit 7fee226ad23 (net: add a noref bit on skb dst) missed one spot
where an skb is enqueued, with a possibly not refcounted dst entry.

__neigh_event_send() inserts skb into arp_queue, so we must make sure
dst entry is refcounted, or dst entry can be freed by garbage collector
after caller exits from rcu protected section.

Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
 net/core/neighbour.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index bff3790..6ba1c0e 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -934,6 +934,7 @@ int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb)
 				kfree_skb(buff);
 				NEIGH_CACHE_STAT_INC(neigh->tbl, unres_discards);
 			}
+			skb_dst_force(skb);
 			__skb_queue_tail(&neigh->arp_queue, skb);
 		}
 		rc = 1;