linux-kernel - Re: BUG: unable to handle kernel NULL pointer dereference in ipv6_select

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Date:	Wed, 21 Dec 2011 21:52:55 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Chris Boot <bootc@...tc.net>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>
Subject: Re: BUG: unable to handle kernel NULL pointer dereference in
 ipv6_select_ident

Le mercredi 21 décembre 2011 à 21:28 +0100, Eric Dumazet a écrit :
> Le mercredi 21 décembre 2011 à 20:05 +0000, Chris Boot a écrit :
> > On 21/12/2011 18:00, Eric Dumazet wrote:
> > > Le mercredi 21 décembre 2011 à 18:36 +0100, Eric Dumazet a écrit :
> > >
> > >> Good point, thats a different problem then, since 3.1 is not supposed to
> > >> have this bug.
> > >>
> > >> It seems rt->rt6i_peer points to invalid memory in your crash.
> > >>
> > >> (RBX=00000000000001f4)
> > >>
> > >> 8b 83 a4 00 00 00       mov    0xa4(%rbx),%eax    p->refcnt
> > >> 1f4+a4 ->  CR2=0000000000000298
> > >>
> > > It would help if you can confirm latest linux tree can reproduce the
> > > bug.
> > 
> > Hi Eric,
> > 
> > I just built a v3.2-rc6-140-gb9e26df with the same config as the Debian 
> > 3.1.0 kernel. I can reproduce the bug just as easily with this kernel as 
> > with the Debian kernel. Unfortunately I wasn't able to get an entire 
> > trace, for some reason it didn't appear to be printed to the serial port 
> > and hung after the (long) list of loaded kernel modules. The crash 
> > happens at the same offset:
> > 
> 
> Thanks !
> 
> Oh well, br_netfilter fake_rtable strikes again.
> 
> I'll cook a patch in a couple of minutes...
> 

Could you try following patch ?

Thanks !

 include/net/dst.h         |    1 +
 net/bridge/br_netfilter.c |    2 +-
 net/ipv4/route.c          |    4 ++--
 net/ipv6/ip6_output.c     |    2 +-
 4 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/net/dst.h b/include/net/dst.h
index 6faec1a..75766b4 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -53,6 +53,7 @@ struct dst_entry {
 #define DST_NOHASH		0x0008
 #define DST_NOCACHE		0x0010
 #define DST_NOCOUNT		0x0020
+#define DST_NOPEER		0x0040
 
 	short			error;
 	short			obsolete;
diff --git a/net/bridge/br_netfilter.c b/net/bridge/br_netfilter.c
index d6ec372..5693e5f 100644
--- a/net/bridge/br_netfilter.c
+++ b/net/bridge/br_netfilter.c
@@ -141,7 +141,7 @@ void br_netfilter_rtable_init(struct net_bridge *br)
 	rt->dst.dev = br->dev;
 	rt->dst.path = &rt->dst;
 	dst_init_metrics(&rt->dst, br_dst_default_metrics, true);
-	rt->dst.flags	= DST_NOXFRM;
+	rt->dst.flags	= DST_NOXFRM | DST_NOPEER;
 	rt->dst.ops = &fake_dst_ops;
 }
 
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 46af623..7720403 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1271,7 +1271,7 @@ void __ip_select_ident(struct iphdr *iph, struct dst_entry *dst, int more)
 {
 	struct rtable *rt = (struct rtable *) dst;
 
-	if (rt) {
+	if (rt && !(rt->dst.flags & DST_NOPEER)) {
 		if (rt->peer == NULL)
 			rt_bind_peer(rt, rt->rt_dst, 1);
 
@@ -1282,7 +1282,7 @@ void __ip_select_ident(struct iphdr *iph, struct dst_entry *dst, int more)
 			iph->id = htons(inet_getid(rt->peer, more));
 			return;
 		}
-	} else
+	} else if (!rt)
 		printk(KERN_DEBUG "rt_bind_peer(0) @%p\n",
 		       __builtin_return_address(0));
 
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 84d0bd5..ec56271 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -603,7 +603,7 @@ void ipv6_select_ident(struct frag_hdr *fhdr, struct rt6_info *rt)
 	static atomic_t ipv6_fragmentation_id;
 	int old, new;
 
-	if (rt) {
+	if (rt && !(rt->dst.flags & DST_NOPEER)) {
 		struct inet_peer *peer;
 
 		if (!rt->rt6i_peer)


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