[RFC PATCH] bridge: netfilter: fix skb->nf_bridge NULL panic in br_nf_forward_finish

[Lin Ming <mlin@ss.pku.edu.cn>]

I can reproduce similiar panic with 3.5-rc5 kernel as Massimo reported at:
http://marc.info/?l=linux-netdev&m=134089242113979&w=2

The steps to reproduce as follow,

1. On Host1, setup brige br0(192.168.1.106)
2. Boot a kvm guest(192.168.1.105) on Host1 and start httpd
3. Start IPVS service on Host1
   ipvsadm -A -t 192.168.1.106:80 -s rr
   ipvsadm -a -t 192.168.1.106:80 -r 192.168.1.105:80 -m
4. Run apache benchmark on Host2(192.168.1.101)
   ab -n 1000 http://192.168.1.106/

The panic happened in br_nf_forward_finish because skb->nf_bridge is NULL.
skb->nf_bridge is set to NULL in ip_vs_reply4 hook.

br_nf_forward_ip():
  NF_HOOK(pf, NF_INET_FORWARD, skb, brnf_get_logical_dev(skb, in), parent,
                br_nf_forward_finish);

This calls IPVS hook ip_vs_reply4.

ip_vs_reply4
  ip_vs_out
    handle_response
      ip_vs_notrack
        nf_reset()
        {
          skb->nf_bridge = NULL;
        }

This patch added skb->nf_bridge check in br_nf_forward_finish and the panic gone.
But I am really not sure if this is the right fix.
Please help to review.

The panic log attached.

[  579.781508] BUG: unable to handle kernel NULL pointer dereference at 0000000000000004
[  579.781669] IP: [<ffffffff817b1ca5>] br_nf_forward_finish+0x58/0x112
[  579.781792] PGD 218f9067 PUD 0 
[  579.781865] Oops: 0000 [#1] SMP 
[  579.781945] CPU 0 
[  579.781983] Modules linked in:
[  579.782047] 
[  579.782080] 
[  579.782114] Pid: 4644, comm: qemu Tainted: G        W    3.5.0-rc5-00006-g95e69f9 #282 Hewlett-Packard  /30E8
[  579.782300] RIP: 0010:[<ffffffff817b1ca5>]  [<ffffffff817b1ca5>] br_nf_forward_finish+0x58/0x112
[  579.782455] RSP: 0018:ffff88007b003a98  EFLAGS: 00010287
[  579.782541] RAX: 0000000000000008 RBX: ffff8800762ead00 RCX: 000000000001670a
[  579.782653] RDX: 0000000000000000 RSI: 000000000000000a RDI: ffff8800762ead00
[  579.782845] RBP: ffff88007b003ac8 R08: 0000000000016630 R09: ffff88007b003a90
[  579.782957] R10: ffff88007b0038e8 R11: ffff88002da37540 R12: ffff88002da01a02
[  579.783066] R13: ffff88002da01a80 R14: ffff88002d83c000 R15: ffff88002d82a000
[  579.783177] FS:  0000000000000000(0000) GS:ffff88007b000000(0063) knlGS:00000000f62d1b70
[  579.783306] CS:  0010 DS: 002b ES: 002b CR0: 000000008005003b
[  579.783395] CR2: 0000000000000004 CR3: 00000000218fe000 CR4: 00000000000027f0
[  579.783505] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  579.783684] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[  579.783795] Process qemu (pid: 4644, threadinfo ffff880021b20000, task ffff880021aba760)
[  579.783919] Stack:
[  579.783959]  ffff88007693cedc ffff8800762ead00 ffff88002da01a02 ffff8800762ead00
[  579.784110]  ffff88002da01a02 ffff88002da01a80 ffff88007b003b18 ffffffff817b26c7
[  579.784260]  ffff880080000000 ffffffff81ef59f0 ffff8800762ead00 ffffffff81ef58b0
[  579.784477] Call Trace:
[  579.784523]  <IRQ> 
[  579.784562] 
[  579.784603]  [<ffffffff817b26c7>] br_nf_forward_ip+0x275/0x2c8
[  579.784707]  [<ffffffff81704b58>] nf_iterate+0x47/0x7d
[  579.784797]  [<ffffffff817ac32e>] ? br_dev_queue_push_xmit+0xae/0xae
[  579.784906]  [<ffffffff81704bfb>] nf_hook_slow+0x6d/0x102
[  579.784995]  [<ffffffff817ac32e>] ? br_dev_queue_push_xmit+0xae/0xae
[  579.785175]  [<ffffffff8187fa95>] ? _raw_write_unlock_bh+0x19/0x1b
[  579.785179]  [<ffffffff817ac417>] __br_forward+0x97/0xa2
[  579.785179]  [<ffffffff817ad366>] br_handle_frame_finish+0x1a6/0x257
[  579.785179]  [<ffffffff817b2386>] br_nf_pre_routing_finish+0x26d/0x2cb
[  579.785179]  [<ffffffff817b2cf0>] br_nf_pre_routing+0x55d/0x5c1
[  579.785179]  [<ffffffff81704b58>] nf_iterate+0x47/0x7d
[  579.785179]  [<ffffffff817ad1c0>] ? br_handle_local_finish+0x44/0x44
[  579.785179]  [<ffffffff81704bfb>] nf_hook_slow+0x6d/0x102
[  579.785179]  [<ffffffff817ad1c0>] ? br_handle_local_finish+0x44/0x44
[  579.785179]  [<ffffffff81551525>] ? sky2_poll+0xb35/0xb54
[  579.785179]  [<ffffffff817ad62a>] br_handle_frame+0x213/0x229
[  579.785179]  [<ffffffff817ad417>] ? br_handle_frame_finish+0x257/0x257
[  579.785179]  [<ffffffff816e3b47>] __netif_receive_skb+0x2b4/0x3f1
[  579.785179]  [<ffffffff816e69fc>] process_backlog+0x99/0x1e2
[  579.785179]  [<ffffffff816e6800>] net_rx_action+0xdf/0x242
[  579.785179]  [<ffffffff8107e8a8>] __do_softirq+0xc1/0x1e0
[  579.785179]  [<ffffffff8135a5ba>] ? trace_hardirqs_off_thunk+0x3a/0x6c
[  579.785179]  [<ffffffff8188812c>] call_softirq+0x1c/0x30

Signed-off-by: Lin Ming <mlin@ss.pku.edu.cn>
---
 net/bridge/br_netfilter.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/net/bridge/br_netfilter.c b/net/bridge/br_netfilter.c
index e41456b..10da415 100644
--- a/net/bridge/br_netfilter.c
+++ b/net/bridge/br_netfilter.c
@@ -719,7 +719,7 @@ static int br_nf_forward_finish(struct sk_buff *skb)
 	struct nf_bridge_info *nf_bridge = skb->nf_bridge;
 	struct net_device *in;
 
-	if (!IS_ARP(skb) && !IS_VLAN_ARP(skb)) {
+	if (!IS_ARP(skb) && !IS_VLAN_ARP(skb) && nf_bridge) {
 		in = nf_bridge->physindev;
 		if (nf_bridge->mask & BRNF_PKT_TYPE) {
 			skb->pkt_type = PACKET_OTHERHOST;
-- 
1.7.2.5