Subject: Re: 2.6.25-rc9: Reported regressions from 2.6.24

From: Patrick McHardy <[email-masked]>
Date: Sun, 13 Apr 2008 22:18:54 +0200

Patrick McHardy wrote:
>>>
>>> Bug-Entry    : http://bugzilla.kernel.org/show_bug.cgi?id=10323
>>> Subject        : panic using bridging on linus kernel 2.6.25-rc6
>>> Submitter    : Andy Gospodarek <[email-masked]>
>>> Date        : 2008-03-25 11:40 (20 days old)
>>
>> This looks like another network-namespace regression.
>> icmp_send() does:
>>
>>        net = rt->u.dst.dev->nd_net;
>>
>> The bridge netfilter code attaches a fake dst_entry to the
>> skb which has dev == NULL when passing it to IPv4 netfilter.
>>
>> Pavel, do you have a better ideas for fixing this than
>> instantiating a dst_entry in br_netfilter.c for every
>> device (or at least for every namespace)? 
>
> The description of the problem was not entirely correct, the
> bridge-netfilter dst_entry does have a proper device pointer,
> it points to a dummy net_device structure however that doesn't
> have a namespace associated with it. This blows up in
> __ip_route_output_key.

For now I suggest this fix. Andy, could you please test whether it
fixes the problem?

[BRIDGE]: Fix crash in __ip_route_output_key with bridge netfilter

The bridge netfilter code attaches a fake dst_entry with a pointer to a
fake net_device structure to skbs it passes up to IPv4 netfilter. This
leads to crashes when the skb is passed to __ip_route_output_key when
dereferencing the namespace pointer.

Since bridging can currently only operate in the init_net namespace,
the easiest fix for now is to initialize the nd_net pointer of the
fake net_device struct to &init_net.

Should fix bugzilla 10323: http://bugzilla.kernel.org/show_bug.cgi?id=10323

Signed-off-by: Patrick McHardy <[email-masked]>

diff --git a/net/bridge/br_netfilter.c b/net/bridge/br_netfilter.c
index 1c0efd8..af7e8be 100644
--- a/net/bridge/br_netfilter.c
+++ b/net/bridge/br_netfilter.c
@@ -110,7 +110,8 @@ static inline __be16 pppoe_proto(const struct sk_buff *skb)
  * ipt_REJECT needs it.  Future netfilter modules might
  * require us to fill additional fields. */
 static struct net_device __fake_net_device = {
-	.hard_header_len	= ETH_HLEN
+	.hard_header_len	= ETH_HLEN,
+	.nd_net			= &init_net,
 };
 
 static struct rtable __fake_rtable = {