linux-kernel - Re: [PATCH net] net: ensure all external references are released in deferred skbuffs

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Date:   Wed, 22 Jun 2022 20:19:08 +0200
From:   Ilya Maximets <i.maximets@....org>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     i.maximets@....org,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Florian Westphal <fw@...len.de>,
        netdev <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>, dev@...nvswitch.org,
        LKML <linux-kernel@...r.kernel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net] net: ensure all external references are released in
 deferred skbuffs

On 6/22/22 19:03, Eric Dumazet wrote:
> On Wed, Jun 22, 2022 at 6:47 PM Eric Dumazet <edumazet@...gle.com> wrote:
>>
>> On Wed, Jun 22, 2022 at 6:39 PM Eric Dumazet <edumazet@...gle.com> wrote:
>>>
>>> On Wed, Jun 22, 2022 at 6:29 PM Eric Dumazet <edumazet@...gle.com> wrote:
>>>>
>>>> On Wed, Jun 22, 2022 at 4:26 PM Ilya Maximets <i.maximets@....org> wrote:
>>>>>
>>>>> On 6/22/22 13:43, Eric Dumazet wrote:
>>>>
>>>>>
>>>>> I tested the patch below and it seems to fix the issue seen
>>>>> with OVS testsuite.  Though it's not obvious for me why this
>>>>> happens.  Can you explain a bit more?
>>>>
>>>> Anyway, I am not sure we can call nf_reset_ct(skb) that early.
>>>>
>>>> git log seems to say that xfrm check needs to be done before
>>>> nf_reset_ct(skb), I have no idea why.
>>>
>>> Additional remark: In IPv6 side, xfrm6_policy_check() _is_ called
>>> after nf_reset_ct(skb)
>>>
>>> Steffen, do you have some comments ?
>>>
>>> Some context:
>>> commit b59c270104f03960069596722fea70340579244d
>>> Author: Patrick McHardy <kaber@...sh.net>
>>> Date:   Fri Jan 6 23:06:10 2006 -0800
>>>
>>>     [NETFILTER]: Keep conntrack reference until IPsec policy checks are done
>>>
>>>     Keep the conntrack reference until policy checks have been performed for
>>>     IPsec NAT support. The reference needs to be dropped before a packet is
>>>     queued to avoid having the conntrack module unloadable.
>>>
>>>     Signed-off-by: Patrick McHardy <kaber@...sh.net>
>>>     Signed-off-by: David S. Miller <davem@...emloft.net>
>>>
>>
>> Oh well... __xfrm_policy_check() has :
>>
>> nf_nat_decode_session(skb, &fl, family);
>>
>> This  answers my questions.
>>
>> This means we are probably missing at least one XFRM check in TCP
>> stack in some cases.
>> (Only after adding this XFRM check we can call nf_reset_ct(skb))
>>
> 
> Maybe this will help ?

I tested this patch and it seems to fix the OVS problem.
I did not test the xfrm part of it.

Will you post an official patch?

> 
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index fe8f23b95d32ca4a35d05166d471327bc608fa91..49c1348e40b6c7b6a98b54d716f29c948e00ba33
> 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -2019,12 +2019,19 @@ int tcp_v4_rcv(struct sk_buff *skb)
>                 if (nsk == sk) {
>                         reqsk_put(req);
>                         tcp_v4_restore_cb(skb);
> -               } else if (tcp_child_process(sk, nsk, skb)) {
> -                       tcp_v4_send_reset(nsk, skb);
> -                       goto discard_and_relse;
>                 } else {
> -                       sock_put(sk);
> -                       return 0;
> +                       if (!xfrm4_policy_check(nsk, XFRM_POLICY_IN, skb)) {
> +                               drop_reason = SKB_DROP_REASON_XFRM_POLICY;
> +                               goto discard_and_relse;
> +                       }
> +                       nf_reset_ct(skb);
> +                       if (tcp_child_process(sk, nsk, skb)) {
> +                               tcp_v4_send_reset(nsk, skb);
> +                               goto discard_and_relse;
> +                       } else {
> +                               sock_put(sk);
> +                               return 0;
> +                       }
>                 }
>         }