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@huawei.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Denis V. Lunev <den@openvz.org>
Link: https://lore.kernel.org/r/20221101121552.21890-1-chenzhongjin@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 3c4786b..a77a85e 100644 (file)
--- 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;