netdev - [PATCH net] net, neigh: Fix null-ptr-deref in neigh_table

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Date:   Tue, 1 Nov 2022 20:15:52 +0800
From:   Chen Zhongjin <chenzhongjin@...wei.com>
To:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <dsahern@...nel.org>, <daniel@...earbox.net>,
        <yangyingliang@...wei.com>, <chenzhongjin@...wei.com>,
        <stephen@...workplumber.org>, <wangyuweihx@...il.com>,
        <alexander.mikhalitsyn@...tuozzo.com>, <den@...nvz.org>,
        <xu.xin16@....com.cn>
Subject: [PATCH net] net, neigh: Fix null-ptr-deref in neigh_table_clear()

When IPv6 module gets initialized but hits an error in the middle,
kenel panic with:

KASAN: null-ptr-deref in range [0x0000000000000598-0x000000000000059f]
CPU: 1 PID: 361 Comm: insmod
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
RIP: 0010:__neigh_ifdown.isra.0+0x24b/0x370
RSP: 0018:ffff888012677908 EFLAGS: 00000202
...
Call Trace:
 <TASK>
 neigh_table_clear+0x94/0x2d0
 ndisc_cleanup+0x27/0x40 [ipv6]
 inet6_init+0x21c/0x2cb [ipv6]
 do_one_initcall+0xd3/0x4d0
 do_init_module+0x1ae/0x670
...
Kernel panic - not syncing: Fatal exception

When ipv6 initialization fails, it will try to cleanup and calls:

neigh_table_clear()
  neigh_ifdown(tbl, NULL)
    pneigh_queue_purge(&tbl->proxy_queue, dev_net(dev == NULL))
    # dev_net(NULL) triggers null-ptr-deref.

Fix it by passing NULL to pneigh_queue_purge() in neigh_ifdown() if dev
is NULL, to make kernel not panic immediately.

Fixes: 66ba215cb513 ("neigh: fix possible DoS due to net iface start/stop loop")
Signed-off-by: Chen Zhongjin <chenzhongjin@...wei.com>
---
 net/core/neighbour.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 3c4786b99907..a77a85e357e0 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -409,7 +409,7 @@ static int __neigh_ifdown(struct neigh_table *tbl, struct net_device *dev,
 	write_lock_bh(&tbl->lock);
 	neigh_flush_dev(tbl, dev, skip_perm);
 	pneigh_ifdown_and_unlock(tbl, dev);
-	pneigh_queue_purge(&tbl->proxy_queue, dev_net(dev));
+	pneigh_queue_purge(&tbl->proxy_queue, dev ? dev_net(dev) : NULL);
 	if (skb_queue_empty_lockless(&tbl->proxy_queue))
 		del_timer_sync(&tbl->proxy_timer);
 	return 0;
-- 
2.17.1