[Patch stable] netfilter: clear skb->next in NF_HOOK_LIST()

[Patch stable] netfilter: clear skb->next in NF_HOOK_LIST()

[Cong Wang]

From: Cong Wang <cong.wang@bytedance.com>

NF_HOOK_LIST() uses list_del() to remove skb from the linked list,
however, it is not sufficient as skb->next still points to other
skb. We should just call skb_list_del_init() to clear skb->next,
like the rest places which using skb list.

This has been fixed in upstream by commit ca58fbe06c54
("netfilter: add and use nf_hook_slow_list()").

Fixes: 9f17dbf04ddf ("netfilter: fix use-after-free in NF_HOOK_LIST")
Reported-by: liuzx@knownsec.com
Tested-by: liuzx@knownsec.com
Cc: Florian Westphal <fw@strlen.de>
Cc: Edward Cree <ecree@solarflare.com>
Cc: stable@vger.kernel.org # between 4.19 and 5.4
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
---
 include/linux/netfilter.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/netfilter.h b/include/linux/netfilter.h
index 77ebb61faf48..4c0e6539effd 100644
--- a/include/linux/netfilter.h
+++ b/include/linux/netfilter.h
@@ -316,7 +316,7 @@ NF_HOOK_LIST(uint8_t pf, unsigned int hook, struct net *net, struct sock *sk,
 
 	INIT_LIST_HEAD(&sublist);
 	list_for_each_entry_safe(skb, next, head, list) {
-		list_del(&skb->list);
+		skb_list_del_init(skb);
 		if (nf_hook(pf, hook, net, sk, skb, in, out, okfn) == 1)
 			list_add_tail(&skb->list, &sublist);
 	}
-- 
2.25.1

Re: [Patch stable] netfilter: clear skb->next in NF_HOOK_LIST()

[Florian Westphal]

Cong Wang <xiyou.wangcong@gmail.com> wrote:
> From: Cong Wang <cong.wang@bytedance.com>
> 
> NF_HOOK_LIST() uses list_del() to remove skb from the linked list,
> however, it is not sufficient as skb->next still points to other
> skb. We should just call skb_list_del_init() to clear skb->next,
> like the rest places which using skb list.
> 
> This has been fixed in upstream by commit ca58fbe06c54
> ("netfilter: add and use nf_hook_slow_list()").

Thanks Cong, agree with this change, afaics its applicable to 4.19.y and 5.4.y.

Re: [Patch stable] netfilter: clear skb->next in NF_HOOK_LIST()

[Sasha Levin]

On Sat, Nov 21, 2020 at 11:22:49PM +0100, Florian Westphal wrote:
>Cong Wang <xiyou.wangcong@gmail.com> wrote:
>> From: Cong Wang <cong.wang@bytedance.com>
>>
>> NF_HOOK_LIST() uses list_del() to remove skb from the linked list,
>> however, it is not sufficient as skb->next still points to other
>> skb. We should just call skb_list_del_init() to clear skb->next,
>> like the rest places which using skb list.
>>
>> This has been fixed in upstream by commit ca58fbe06c54
>> ("netfilter: add and use nf_hook_slow_list()").
>
>Thanks Cong, agree with this change, afaics its applicable to 4.19.y and 5.4.y.

Queued for 5.4 and 4.19, thanks!

-- 
Thanks,
Sasha

Re: [Patch stable] netfilter: clear skb->next in NF_HOOK_LIST()

[Greg Kroah-Hartman]

On Sat, Nov 28, 2020 at 05:09:18PM +0800, 刘志旭 wrote:
> I still didn't see this patch in stable queue yet. Since we've a working POC to panic the 
> system (see https://bugzilla.kernel.org/show_bug.cgi?id=209823), I think it's necessary
> to merge this patch ASAP, thanks.

Odd, I don't think Sasha pushed out his patch queue.  I've applied this
now, thanks.

greg k-h