On Wed, Sep 23, 2015 at 2:00 PM, Eric Dumazet <eric.duma...@gmail.com> wrote:
> From: Eric Dumazet <eduma...@google.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 <eduma...@google.com>
Acked-by: Yuchung Cheng <ych...@google.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);
>
>
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