netdev - Re: [PATCH v3 net-next] net: Find dst with sk's xfrm policy not ctl

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Date:   Wed, 6 Jul 2022 08:59:58 -0600
From:   David Ahern <dsahern@...nel.org>
To:     Eric Dumazet <edumazet@...gle.com>, Sewook Seo <ssewook@...il.com>
Cc:     Sewook Seo <sewookseo@...gle.com>,
        Linux Network Development Mailing List 
        <netdev@...r.kernel.org>, "David S . Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Maciej Żenczykowski <maze@...gle.com>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Sehee Lee <seheele@...gle.com>
Subject: Re: [PATCH v3 net-next] net: Find dst with sk's xfrm policy not
 ctl_sk

On 7/6/22 1:19 AM, Eric Dumazet wrote:
> On Wed, Jul 6, 2022 at 8:34 AM Sewook Seo <ssewook@...il.com> wrote:
>>
>> From: sewookseo <sewookseo@...gle.com>
>>
>> If we set XFRM security policy by calling setsockopt with option
>> IPV6_XFRM_POLICY, the policy will be stored in 'sock_policy' in 'sock'
>> struct. However tcp_v6_send_response doesn't look up dst_entry with the
>> actual socket but looks up with tcp control socket. This may cause a
>> problem that a RST packet is sent without ESP encryption & peer's TCP
>> socket can't receive it.
>> This patch will make the function look up dest_entry with actual socket,
>> if the socket has XFRM policy(sock_policy), so that the TCP response
>> packet via this function can be encrypted, & aligned on the encrypted
>> TCP socket.
>>
>> Tested: We encountered this problem when a TCP socket which is encrypted
>> in ESP transport mode encryption, receives challenge ACK at SYN_SENT
>> state. After receiving challenge ACK, TCP needs to send RST to
>> establish the socket at next SYN try. But the RST was not encrypted &
>> peer TCP socket still remains on ESTABLISHED state.
>> So we verified this with test step as below.
>> [Test step]
>> 1. Making a TCP state mismatch between client(IDLE) & server(ESTABLISHED).
>> 2. Client tries a new connection on the same TCP ports(src & dst).
>> 3. Server will return challenge ACK instead of SYN,ACK.
>> 4. Client will send RST to server to clear the SOCKET.
>> 5. Client will retransmit SYN to server on the same TCP ports.
>> [Expected result]
>> The TCP connection should be established.
>>
>> Effort: net
> 
> Please remove this Effort: tag, this is not appropriate for upstream patches.
> 
>> Cc: Maciej Żenczykowski <maze@...gle.com>
>> Cc: Eric Dumazet <edumazet@...gle.com>
>> Cc: Steffen Klassert <steffen.klassert@...unet.com>
>> Cc: Sehee Lee <seheele@...gle.com>
>> Signed-off-by: Sewook Seo <sewookseo@...gle.com>
>> ---
>>  net/ipv4/ip_output.c | 7 ++++++-
>>  net/ipv4/tcp_ipv4.c  | 5 +++++
>>  net/ipv6/tcp_ipv6.c  | 7 ++++++-
>>  3 files changed, 17 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
>> index 00b4bf26fd93..1da430c8fee2 100644
>> --- a/net/ipv4/ip_output.c
>> +++ b/net/ipv4/ip_output.c
>> @@ -1704,7 +1704,12 @@ void ip_send_unicast_reply(struct sock *sk, struct sk_buff *skb,
>>                            tcp_hdr(skb)->source, tcp_hdr(skb)->dest,
>>                            arg->uid);
>>         security_skb_classify_flow(skb, flowi4_to_flowi_common(&fl4));
>> -       rt = ip_route_output_key(net, &fl4);
>> +#ifdef CONFIG_XFRM
>> +       if (sk->sk_policy[XFRM_POLICY_OUT])
>> +               rt = ip_route_output_flow(net, &fl4, sk);
>> +       else
>> +#endif
>> +               rt = ip_route_output_key(net, &fl4);
> 
> I really do not like adding more #ifdef
> 
> What happens if we simply use :
> 
>       rt = ip_route_output_flow(net, &fl4, sk);
> 

That should be fine - and simpler solution.


>> diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
>> index c72448ba6dc9..8b8819c3d2c2 100644
>> --- a/net/ipv6/tcp_ipv6.c
>> +++ b/net/ipv6/tcp_ipv6.c
>> @@ -952,7 +952,12 @@ static void tcp_v6_send_response(const struct sock *sk, struct sk_buff *skb, u32
>>          * Underlying function will use this to retrieve the network
>>          * namespace
>>          */
>> -       dst = ip6_dst_lookup_flow(sock_net(ctl_sk), ctl_sk, &fl6, NULL);
>> +#ifdef CONFIG_XFRM
>> +       if (sk && sk->sk_policy[XFRM_POLICY_OUT] && sk_fullsock(sk))
>> +               dst = ip6_dst_lookup_flow(net, sk, &fl6, NULL);  /* Get dst with sk's XFRM policy */
>> +       else
>> +#endif
>> +               dst = ip6_dst_lookup_flow(sock_net(ctl_sk), ctl_sk, &fl6, NULL);
> 
> and then:
> 
>      dst = ip6_dst_lookup_flow(net, sk, &fl6, NULL);

same here.