[Devel] [PATCH vz7 v3 1/2] net, neigh: Fix null-ptr-deref in neigh_table_clear()

[Pavel Tikhomirov]

(for both patches)
Reviewed-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>

On 17/01/2024 03:31, Alexander Atanasov wrote:
> From: Chen Zhongjin <chenzhongjin at huawei.com>
> 
> 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 at huawei.com>
> Reviewed-by: Eric Dumazet <edumazet at google.com>
> Reviewed-by: Denis V. Lunev <den at openvz.org>
> Link: https://lore.kernel.org/r/20221101121552.21890-1-chenzhongjin@huawei.com
> Signed-off-by: Jakub Kicinski <kuba at kernel.org>
> (cherry picked from commit f8017317cb0b279b8ab98b0f3901a2e0ac880dad)
> https://virtuozzo.atlassian.net/browse/PSBM-153018
> https://bugs.openvz.org/browse/OVZ-7410
> Signed-off-by: Alexander Atanasov <alexander.atanasov at virtuozzo.com>
> ---
>   net/core/neighbour.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> 
> v1->v2: fixed wrong merge
> v2->v3: backported one more patch - which is not in the vz7 tree but is in mainstream,
> so it looked like two patches are made into one. Both touch the same code to increase
> the confusion.
> 
> 
> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> index d5b28c158144..ae6490f8d3ae 100644
> --- a/net/core/neighbour.c
> +++ b/net/core/neighbour.c
> @@ -321,7 +321,7 @@ int neigh_ifdown(struct neigh_table *tbl, struct net_device *dev)
>   	neigh_flush_dev(tbl, dev);
>   	pneigh_ifdown(tbl, dev);
>   	write_unlock_bh(&tbl->lock);
> -	pneigh_queue_purge(&tbl->proxy_queue, dev_net(dev));
> +	pneigh_queue_purge(&tbl->proxy_queue, dev ? dev_net(dev) : NULL);
>   	if (skb_queue_empty(&tbl->proxy_queue))
>   		del_timer_sync(&tbl->proxy_timer);
>   	return 0;

-- 
Best regards, Tikhomirov Pavel
Senior Software Developer, Virtuozzo.