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

[Eric Dumazet]

On Tue, Nov 1, 2022 at 5:19 AM Chen Zhongjin <chenzhongjin@xxxxxxxxxx> 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@xxxxxxxxxx>
> ---

SGTM, thanks !

Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>