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 21:30:19 +0000
From:   서세욱 <ssewook@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Sewook Seo <sewookseo@...gle.com>,
        David Ahern <dsahern@...nel.org>,
        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

Hi, Eric.

Wow great, all suggestions to remove #ifdef are possible & look much better.
I'll amend it.

Thank you.


2022년 7월 6일 (수) 오후 3:00, David Ahern <dsahern@...nel.org>님이 작성:
>
> 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.