Re: [PATCH net] net, neigh: Fix null-ptr-deref in neigh_table_clear()

["Denis V. Lunev" <den@virtuozzo.com>]

On 11/1/22 13:15, Chen Zhongjin wrote:
> 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>
> ---
>   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;
Reviewed-by: Denis V. Lunev <den@openvz.org>