netdev - Re: bridge netfilter output bug on 2.6.39

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Date:	Tue, 24 May 2011 18:46:27 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	David Miller <davem@...emloft.net>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	netdev@...r.kernel.org
Subject: Re: bridge netfilter output bug on 2.6.39

Le mardi 24 mai 2011 à 18:27 +0200, Eric Dumazet a écrit :
> Le mardi 24 mai 2011 à 17:39 +0200, Eric Dumazet a écrit :
> 
> > I would say its more likely a problem with dst metrics changes
> > 
> > In this crash, we dereference a NULL dst->_metrics 'pointer' in
> > dst_metric_raw(dst, RTAX_MTU);
> 
> It seems bridge code uses one fake_rtable
> 
> You probably want to properly init its _metric field.
> 
> I can do the patch in one hour eventually, if nobody beats me.
> 
> 

Here is the patch :

[PATCH] bridge: initialize fake_rtable metrics

bridge netfilter code uses a fake_rtable, and we must init its _metric
field or risk NULL dereference later.

Ref: https://bugzilla.kernel.org/show_bug.cgi?id=35672

Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
CC: Stephen Hemminger <shemminger@...tta.com>
CC: Herbert Xu <herbert@...dor.apana.org.au>
---
 net/bridge/br_netfilter.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/bridge/br_netfilter.c b/net/bridge/br_netfilter.c
index e1f5ec7..3fa1231 100644
--- a/net/bridge/br_netfilter.c
+++ b/net/bridge/br_netfilter.c
@@ -117,6 +117,10 @@ static struct dst_ops fake_dst_ops = {
  * ipt_REJECT needs it.  Future netfilter modules might
  * require us to fill additional fields.
  */
+static const u32 br_dst_default_metrics[RTAX_MAX] = {
+	[RTAX_MTU - 1] = 1500,
+};
+
 void br_netfilter_rtable_init(struct net_bridge *br)
 {
 	struct rtable *rt = &br->fake_rtable;
@@ -124,7 +128,7 @@ void br_netfilter_rtable_init(struct net_bridge *br)
 	atomic_set(&rt->dst.__refcnt, 1);
 	rt->dst.dev = br->dev;
 	rt->dst.path = &rt->dst;
-	dst_metric_set(&rt->dst, RTAX_MTU, 1500);
+	dst_init_metrics(&rt->dst, br_dst_default_metrics, true);
 	rt->dst.flags	= DST_NOXFRM;
 	rt->dst.ops = &fake_dst_ops;
 }


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