netdev - Re: [PATCH v2 net] tcp: add proper TS val into RST packets

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAK6E8=eGveAnOJKcvX6i+DNS0HYiOBW0nKeOxNFGg_+R1h2rFg@mail.gmail.com>
Date:	Wed, 23 Sep 2015 14:13:35 -0700
From:	Yuchung Cheng <ycheng@...gle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Neal Cardwell <ncardwell@...gle.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 net] tcp: add proper TS val into RST packets

On Wed, Sep 23, 2015 at 2:00 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> From: Eric Dumazet <edumazet@...gle.com>
>
> RST packets sent on behalf of TCP connections with TS option (RFC 7323
> TCP timestamps) have incorrect TS val (set to 0), but correct TS ecr.
>
> A > B: Flags [S], seq 0, win 65535, options [mss 1000,nop,nop,TS val 100
> ecr 0], length 0
> B > A: Flags [S.], seq 2444755794, ack 1, win 28960, options [mss
> 1460,nop,nop,TS val 7264344 ecr 100], length 0
> A > B: Flags [.], ack 1, win 65535, options [nop,nop,TS val 110 ecr
> 7264344], length 0
>
> B > A: Flags [R.], seq 1, ack 1, win 28960, options [nop,nop,TS val 0
> ecr 110], length 0
>
> We need to call skb_mstamp_get() to get proper TS val,
> derived from skb->skb_mstamp
>
> Note that RFC 1323 was advocating to not send TS option in RST segment,
> but RFC 7323 recommends the opposite :
>
>   Once TSopt has been successfully negotiated, that is both <SYN> and
>   <SYN,ACK> contain TSopt, the TSopt MUST be sent in every non-<RST>
>   segment for the duration of the connection, and SHOULD be sent in an
>   <RST> segment (see Section 5.2 for details)
>
> Note this RFC recommends to send TS val = 0, but we believe it is
> premature : We do not know if all TCP stacks are properly
> handling the receive side :
>
>    When an <RST> segment is
>    received, it MUST NOT be subjected to the PAWS check by verifying an
>    acceptable value in SEG.TSval, and information from the Timestamps
>    option MUST NOT be used to update connection state information.
>    SEG.TSecr MAY be used to provide stricter <RST> acceptance checks.
>
>
> In 5 years, if/when all TCP stack are RFC 7323 ready, we might consider
> to decide to send TS val = 0, if it buys something.
>
> Fixes: 7faee5c0d514 ("tcp: remove TCP_SKB_CB(skb)->when")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Acked-by: Yuchung Cheng <ycheng@...gle.com>

Nice fix (and comment)!

> ---
>  net/ipv4/tcp_output.c |    1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index f9a8a12b62ee..1100ffe4a722 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -2897,6 +2897,7 @@ void tcp_send_active_reset(struct sock *sk, gfp_t priority)
>         skb_reserve(skb, MAX_TCP_HEADER);
>         tcp_init_nondata_skb(skb, tcp_acceptable_seq(sk),
>                              TCPHDR_ACK | TCPHDR_RST);
> +       skb_mstamp_get(&skb->skb_mstamp);
>         /* Send it off. */
>         if (tcp_transmit_skb(sk, skb, 0, priority))
>                 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTFAILED);
>
>
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html