[PATCH] net bridge: add null pointer check, fix panic

xiaoming gao
Thu, 20 Jun 2013 03:08:11 -0000

From: newtongao <newtongao@tencent.com>
Date: Wed, 19 Jun 2013 14:58:33 +0800
Subject: [PATCH] net bridge: add null pointer check,fix panic

in kernel 3.0, br_port_get_rcu() may return NULL when network interface be
deleting from bridge,
but in function br_handle_frame and br_handle_local_finish, the pointer
didn''t be checked before using,
so all br_port_get_rcu callers must do null check,or there occurs the null
pointer panic.

kernel 3.4 also has this bug,i have verified.
mainline kernel still did not  check br_port_get_rcu()''s NULL pointer,
but i have not tested it yet.

method to reproduce null pointer panic:
1. in function del_nbp,amplify the gap between "dev->priv_flags &=
~IFF_BRIDGE_PORT;" and "netdev_rx_handler_unregister(dev);" ,
such as add new line "while(1);".
2. create net bridge testbr and bind some network interface(e.g. testif) on it.
3. send packets to testif frequetly,such as ping testif.
4. brctl delif testbr testif.

backtrace:
[1002130.426411] FS:  00007f2235153700(0000) GS:ffff88007b020000(0000)
knlGS:0000000000000000
[1002130.524656] CS:  e033 DS: 0000 ES: 0000 CR0: 000000008005003b
[1002130.594931] CR2: 0000000000000021 CR3: 0000000001dc7000 CR4:
0000000000002660
[1002130.681798] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
0000000000000000
[1002130.768654] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7:
0000000000000400
[1002130.855525] Process ksoftirqd/1 (pid: 9, threadinfo ffff880062642000, task
ffff880062640800)
[1002130.957868] Stack:
[1002130.983758]  0000000080000000 ffff88007bc06a40 ffff88005e3c6c80
ffffffff81901d10
[1002131.073887]  ffff88005efc2000 0000000000000001 ffff880062643bf0
ffffffff818497d9
[1002131.163945]  ffff88006147e090 0000000000000020 ffff88007bc06a40
ffff88005e3c6c80
[1002131.254023] Call Trace:
[1002131.285086]  [<ffffffff81901d10>] ?
br_handle_frame_finish+0x2b0/0x2b0
[1002131.364677]  [<ffffffff818497d9>] __netif_receive_skb+0x109/0x4a0
[1002131.439081]  [<ffffffff81849b12>] __netif_receive_skb+0x442/0x4a0
[1002131.513493]  [<ffffffff810e3a6e>] ? __kmalloc_node+0x3e/0x50
[1002131.582744]  [<ffffffff8184b7d8>] netif_receive_skb+0x78/0x80
[1002131.653053]  [<ffffffff8184b928>] napi_skb_finish+0x48/0x60
[1002131.721269]  [<ffffffff8184bf1d>] napi_gro_receive+0xfd/0x130
[1002131.791551]  [<ffffffff8192b2f6>] vlan_gro_receive+0x16/0x20
[1002131.860796]  [<ffffffff816a41d1>] igb_poll+0x6f1/0xdc0
[1002131.923871]  [<ffffffff8196c0d5>] ? __schedule+0x2e5/0x810
[1002131.991071]  [<ffffffff8196e38b>] ? _raw_spin_lock_irq+0xb/0x30
[1002132.063421]  [<ffffffff8184c0c1>] net_rx_action+0xa1/0x1d0
[1002132.130619]  [<ffffffff81057449>] __do_softirq+0x99/0x130
[1002132.196803]  [<ffffffff8105759a>] run_ksoftirqd+0xba/0x170
[1002132.264000]  [<ffffffff810574e0>] ? __do_softirq+0x130/0x130
[1002132.333258]  [<ffffffff8106d306>] kthread+0x96/0xa0
[1002132.393224]  [<ffffffff8196ffe4>] kernel_thread_helper+0x4/0x10
[1002132.465580]  [<ffffffff8196f0f6>] ? int_ret_from_sys_call+0x7/0x1b
[1002132.541016]  [<ffffffff8196e8a1>] ? retint_restore_args+0x5/0x6
[1002132.613368]  [<ffffffff8196ffe0>] ? gs_change+0x13/0x13
[1002132.677466] Code: 02 f6 81 a5 01 00 00 40 48 8b 81 e0 02 00 00 89 d6 4c 0f
45 f0 48 8b 05 50 76 20 00 66 33 70 04 66 f7 c6 ff f0 0f 84 d0 00 00 00
[1002132.835500]  0f b6 46 21 3c 02 74 50 3c 03 0f 85 60 ff ff ff 48 8b 05 e1
[1002132.920864] RIP  [<ffffffff81901e17>] br_handle_frame+0x107/0x260
[1002132.995296]  RSP <ffff880062643b50>
[1002133.038735] CR2: 0000000000000021

Signed-off-by: Xiaoming Gao <newtongao@tencent.com>
---
 net/bridge/br_input.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
index f06ee39..c8b365f 100644
--- a/net/bridge/br_input.c
+++ b/net/bridge/br_input.c
@@ -122,7 +122,8 @@ static int br_handle_local_finish(struct sk_buff *skb)
 {
 	struct net_bridge_port *p = br_port_get_rcu(skb->dev);

-	br_fdb_update(p->br, p, eth_hdr(skb)->h_source);
+	if (p)
+		br_fdb_update(p->br, p, eth_hdr(skb)->h_source);
 	return 0;	 /* process further */
 }

@@ -160,6 +161,8 @@ rx_handler_result_t br_handle_frame(struct sk_buff **pskb)
 		return RX_HANDLER_CONSUMED;

 	p = br_port_get_rcu(skb->dev);
+	if (!p)
+		goto drop;

 	if (unlikely(is_link_local(dest))) {
 		/* Pause frames shouldn''t be passed up by driver anyway */
--
1.7.1