netdev - [PATCH net] netfilter: br_netfilter: reread nf

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Message-ID: <20250820043329.2902014-1-wangliang74@huawei.com>
Date: Wed, 20 Aug 2025 12:33:29 +0800
From: Wang Liang <wangliang74@...wei.com>
To: <pablo@...filter.org>, <kadlec@...filter.org>, <fw@...len.de>,
	<razor@...ckwall.org>, <idosch@...dia.com>, <davem@...emloft.net>,
	<edumazet@...gle.com>, <kuba@...nel.org>, <pabeni@...hat.com>,
	<horms@...nel.org>
CC: <yuehaibing@...wei.com>, <zhangchangzhong@...wei.com>,
	<wangliang74@...wei.com>, <netfilter-devel@...r.kernel.org>,
	<coreteam@...filter.org>, <bridge@...ts.linux.dev>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH net] netfilter: br_netfilter: reread nf_conn from skb after confirm()

Previous commit 2d72afb34065 ("netfilter: nf_conntrack: fix crash due to
removal of uninitialised entry") move the IPS_CONFIRMED assignment after
the hash table insertion.

When send a broadcast packet to a tap device, which was added to a bridge,
br_nf_local_in() is called to confirm the conntrack. If another conntrack
with the same hash value is added to the hash table, which can be
triggered by a normal packet to a non-bridge device, the below warning
may happen.

  ------------[ cut here ]------------
  WARNING: CPU: 1 PID: 96 at net/bridge/br_netfilter_hooks.c:632 br_nf_local_in+0x168/0x200
  CPU: 1 UID: 0 PID: 96 Comm: tap_send Not tainted 6.17.0-rc2-dirty #44 PREEMPT(voluntary)
  RIP: 0010:br_nf_local_in+0x168/0x200
  Call Trace:
   <TASK>
   nf_hook_slow+0x3e/0xf0
   br_pass_frame_up+0x103/0x180
   br_handle_frame_finish+0x2de/0x5b0
   br_nf_hook_thresh+0xc0/0x120
   br_nf_pre_routing_finish+0x168/0x3a0
   br_nf_pre_routing+0x237/0x5e0
   br_handle_frame+0x1ec/0x3c0
   __netif_receive_skb_core+0x225/0x1210
   __netif_receive_skb_one_core+0x37/0xa0
   netif_receive_skb+0x36/0x160
   tun_get_user+0xa54/0x10c0
   tun_chr_write_iter+0x65/0xb0
   vfs_write+0x305/0x410
   ksys_write+0x60/0xd0
   do_syscall_64+0xa4/0x260
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
   </TASK>
  ---[ end trace 0000000000000000 ]---

To solve the hash conflict, nf_ct_resolve_clash() try to merge the
conntracks, and update skb->_nfct. However, br_nf_local_in() still use the
old ct from local variable 'nfct' after confirm(), which leads to this
issue. Fix it by rereading nfct from skb.

Fixes: 62e7151ae3eb ("netfilter: bridge: confirm multicast packets before passing them up the stack")
Signed-off-by: Wang Liang <wangliang74@...wei.com>
---
 net/bridge/br_netfilter_hooks.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/bridge/br_netfilter_hooks.c b/net/bridge/br_netfilter_hooks.c
index 94cbe967d1c1..55b1b7dcb609 100644
--- a/net/bridge/br_netfilter_hooks.c
+++ b/net/bridge/br_netfilter_hooks.c
@@ -626,6 +626,7 @@ static unsigned int br_nf_local_in(void *priv,
 		break;
 	}
 
+	nfct = skb_nfct(skb);
 	ct = container_of(nfct, struct nf_conn, ct_general);
 	WARN_ON_ONCE(!nf_ct_is_confirmed(ct));
 
-- 
2.33.0