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

On Wed, Sep 23, 2015 at 1:30 PM, Neal Cardwell [off-list ref] wrote:

On Wed, Sep 23, 2015 at 4:19 PM, Eric Dumazet [off-list ref] wrote:

quoted

From: Eric Dumazet <redacted>

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)

Nice comment. I think it's worth adding why we choose not to follow
RFC7323 sec 5.2 recommendation on setting TSval to 0?

quoted

Fixes: 7faee5c0d514 ("tcp: remove TCP_SKB_CB(skb)->when")
Signed-off-by: Eric Dumazet <redacted>
---

Acked-by: Neal Cardwell <ncardwell@google.com>

Thanks, Eric!

neal