netdev - Re: [PATCH v2] net-tcp: Find dst with sk's xfrm policy not ctl

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Date:   Tue, 05 Jul 2022 10:25:47 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Sewook Seo <ssewook@...il.com>, Sewook Seo <sewookseo@...gle.com>
Cc:     Linux Network Development Mailing List <netdev@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Maciej Żenczykowski <maze@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Sehee Lee <seheele@...gle.com>
Subject: Re: [PATCH v2] net-tcp: Find dst with sk's xfrm policy not ctl_sk

Hello,

On Fri, 2022-07-01 at 15:44 +0000, Sewook Seo 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-tcp

This looks like a stray "internal" tag?

> 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>

Is this targeting -net -or -net-next? IMHO this could land in either
trees. If you are targting net, please add a suitable Fixes: tag.


> ---
> Changelog since v1:
> - Remove unnecessary null check of sk at ip_output.c
>   Narrow down patch scope: sending RST at SYN_SENT state
>   Remove unnecessay condition to call xfrm_sk_free_policy()
>   Verified at KASAN build
> 
>  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);
>  	if (IS_ERR(rt))
>  		return;
>  
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index fda811a5251f..459669f9e13f 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -819,6 +819,10 @@ static void tcp_v4_send_reset(const struct sock *sk, struct sk_buff *skb)
>  		ctl_sk->sk_priority = (sk->sk_state == TCP_TIME_WAIT) ?
>  				   inet_twsk(sk)->tw_priority : sk->sk_priority;
>  		transmit_time = tcp_transmit_time(sk);
> +#ifdef CONFIG_XFRM
> +		if (sk->sk_policy[XFRM_POLICY_OUT] && sk->sk_state == TCP_SYN_SENT)
> +			xfrm_sk_clone_policy(ctl_sk, sk);
> +#endif

It looks like the cloned policy will be overwrited by later resets and
possibly leaked? nobody calls xfrm_sk_free_policy() on the old policy.

Thanks!

Paolo