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

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Submitter Eric Dumazet
Date May 27, 2010, 8:18 p.m.
Message ID <1274991504.2446.13.camel@edumazet-laptop>
Download mbox | patch
Permalink /patch/53780/
State Accepted
Delegated to: David Miller
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Comments

Eric Dumazet - May 27, 2010, 8:18 p.m.
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(+)



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David Miller - May 27, 2010, 11:10 p.m.
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Thu, 27 May 2010 22:18:24 +0200

> [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>

Applied, thanks Eric.

Ingo can we get a confirmation that this fixes the bootup crash?

Thanks!
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Ingo Molnar - May 28, 2010, 8:05 a.m.
* David Miller <davem@davemloft.net> wrote:

> From: Eric Dumazet <eric.dumazet@gmail.com>
> Date: Thu, 27 May 2010 22:18:24 +0200
> 
> > [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>
> 
> Applied, thanks Eric.
> 
> Ingo can we get a confirmation that this fixes the bootup crash?

Sure, will let you know how it goes.

Thanks,

	Ingo
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Ingo Molnar - May 28, 2010, 8:24 a.m.
* Ingo Molnar <mingo@elte.hu> wrote:

> 
> * David Miller <davem@davemloft.net> wrote:
> 
> > From: Eric Dumazet <eric.dumazet@gmail.com>
> > Date: Thu, 27 May 2010 22:18:24 +0200
> > 
> > > [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>
> > 
> > Applied, thanks Eric.
> > 
> > Ingo can we get a confirmation that this fixes the bootup crash?
> 
> Sure, will let you know how it goes.

Preliminary testing shows that Eric's patch solves the problem.

Tested-by: Ingo Molnar <mingo@elte.hu>

Thanks!

	Ingo
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David Miller - May 28, 2010, 8:53 a.m.
From: Ingo Molnar <mingo@elte.hu>
Date: Fri, 28 May 2010 10:24:40 +0200

> Preliminary testing shows that Eric's patch solves the problem.
> 
> Tested-by: Ingo Molnar <mingo@elte.hu>

Thanks a lot for testing Ingo.
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Patch

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;