Subject: Re: Yet another bridge netfilter crash

From: Patrick McHardy <[email-masked]>
Date: Fri, 23 Jul 2010 16:18:46 +0200

On 23.07.2010 15:42, Herbert Xu wrote:
> Hi:
> 
> I was cced on the following bug:
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=617268
> 
>>>From what I've seen in the crash dump, this would appear to be
> yet another manifestation of the evil relationship between the
> bridge and IPv4 through netfilter.
> 
> In particular, bridge netfilter invokes IPv4's PRE_ROUTING rules,
> one of which assembles packets for connection tracking.
> 
> Unfortunately, the same cache is used for reassembling bridge
> packets and non-bridge packets.
> 
> Now we already knew about this and its potential security effects.
> However, what we didn't know is that this can also cause a packet
> to appear in the bridge pre_routing code with nf_bridge set to
> NULL when it must not be NULL.
> 
> This happens if the non-bridge fragment appeared first.
> 
> So now is the time to fix this properly by giving the bridge its
> own separate conntrack namespace/zone.

I think we've already fixed this by commit 8fa9ff6:

commit 8fa9ff6849bb86c59cc2ea9faadf3cb2d5223497
Author: Patrick McHardy <[email-masked]>
Date:   Tue Dec 15 16:59:59 2009 +0100

    netfilter: fix crashes in bridge netfilter caused by fragment jumps
    
    When fragments from bridge netfilter are passed to IPv4 or IPv6 conntrack
    and a reassembly queue with the same fragment key already exists from
    reassembling a similar packet received on a different device (f.i. with
    multicasted fragments), the reassembled packet might continue on a different
    codepath than where the head fragment originated. This can cause crashes
    in bridge netfilter when a fragment received on a non-bridge device (and
    thus with skb->nf_bridge == NULL) continues through the bridge netfilter
    code.
    
    Add a new reassembly identifier for packets originating from bridge
    netfilter and use it to put those packets in insolated queues.
    
    Fixes http://bugzilla.kernel.org/show_bug.cgi?id=14805
    
    Reported-and-Tested-by: Chong Qiao <[email-masked]>
    Signed-off-by: Patrick McHardy <[email-masked]>

diff --git a/include/net/ip.h b/include/net/ip.h
index e6b9d12..85108cf 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -337,6 +337,7 @@ enum ip_defrag_users {
 	IP_DEFRAG_CALL_RA_CHAIN,
 	IP_DEFRAG_CONNTRACK_IN,
 	IP_DEFRAG_CONNTRACK_OUT,
+	IP_DEFRAG_CONNTRACK_BRIDGE_IN,
 	IP_DEFRAG_VS_IN,
 	IP_DEFRAG_VS_OUT,
 	IP_DEFRAG_VS_FWD
diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index d691603..ccab594 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -354,6 +354,7 @@ enum ip6_defrag_users {
 	IP6_DEFRAG_LOCAL_DELIVER,
 	IP6_DEFRAG_CONNTRACK_IN,
 	IP6_DEFRAG_CONNTRACK_OUT,
+	IP6_DEFRAG_CONNTRACK_BRIDGE_IN,
 };
 
 struct ip6_create_arg {
diff --git a/net/ipv4/netfilter/nf_defrag_ipv4.c b/net/ipv4/netfilter/nf_defrag_ipv4.c
index fa2d6b6..331ead3 100644
--- a/net/ipv4/netfilter/nf_defrag_ipv4.c
+++ b/net/ipv4/netfilter/nf_defrag_ipv4.c
@@ -14,6 +14,7 @@
 #include <net/route.h>
 #include <net/ip.h>
 
+#include <linux/netfilter_bridge.h>
 #include <linux/netfilter_ipv4.h>
 #include <net/netfilter/ipv4/nf_defrag_ipv4.h>
 
@@ -34,6 +35,20 @@ static int nf_ct_ipv4_gather_frags(struct sk_buff *skb, u_int32_t user)
 	return err;
 }
 
+static enum ip_defrag_users nf_ct_defrag_user(unsigned int hooknum,
+					      struct sk_buff *skb)
+{
+#ifdef CONFIG_BRIDGE_NETFILTER
+	if (skb->nf_bridge &&
+	    skb->nf_bridge->mask & BRNF_NF_BRIDGE_PREROUTING)
+		return IP_DEFRAG_CONNTRACK_BRIDGE_IN;
+#endif
+	if (hooknum == NF_INET_PRE_ROUTING)
+		return IP_DEFRAG_CONNTRACK_IN;
+	else
+		return IP_DEFRAG_CONNTRACK_OUT;
+}
+
 static unsigned int ipv4_conntrack_defrag(unsigned int hooknum,
 					  struct sk_buff *skb,
 					  const struct net_device *in,
@@ -50,10 +65,8 @@ static unsigned int ipv4_conntrack_defrag(unsigned int hooknum,
 #endif
 	/* Gather fragments. */
 	if (ip_hdr(skb)->frag_off & htons(IP_MF | IP_OFFSET)) {
-		if (nf_ct_ipv4_gather_frags(skb,
-					    hooknum == NF_INET_PRE_ROUTING ?
-					    IP_DEFRAG_CONNTRACK_IN :
-					    IP_DEFRAG_CONNTRACK_OUT))
+		enum ip_defrag_users user = nf_ct_defrag_user(hooknum, skb);
+		if (nf_ct_ipv4_gather_frags(skb, user))
 			return NF_STOLEN;
 	}
 	return NF_ACCEPT;
diff --git a/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c b/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c
index c0a82fe..0956eba 100644
--- a/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c
+++ b/net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c
@@ -20,6 +20,7 @@
 #include <net/ipv6.h>
 #include <net/inet_frag.h>
 
+#include <linux/netfilter_bridge.h>
 #include <linux/netfilter_ipv6.h>
 #include <net/netfilter/nf_conntrack.h>
 #include <net/netfilter/nf_conntrack_helper.h>
@@ -190,6 +191,11 @@ out:
 static enum ip6_defrag_users nf_ct6_defrag_user(unsigned int hooknum,
 						struct sk_buff *skb)
 {
+#ifdef CONFIG_BRIDGE_NETFILTER
+	if (skb->nf_bridge &&
+	    skb->nf_bridge->mask & BRNF_NF_BRIDGE_PREROUTING)
+		return IP6_DEFRAG_CONNTRACK_BRIDGE_IN;
+#endif
 	if (hooknum == NF_INET_PRE_ROUTING)
 		return IP6_DEFRAG_CONNTRACK_IN;
 	else