netdev - Re: [PATCH net 2/2] net-timestamp: fix missing tcp fragmentation cases

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Date:	Tue, 12 Aug 2014 12:00:26 -0700
From:	Willem de Bruijn <willemb@...gle.com>
To:	Network Development <netdev@...r.kernel.org>
Cc:	David Miller <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Richard Cochran <richardcochran@...il.com>,
	Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net 2/2] net-timestamp: fix missing tcp fragmentation cases

On Tue, Aug 12, 2014 at 11:53 AM, Willem de Bruijn <willemb@...gle.com> wrote:
> Bytestream timestamps are correlated with a single byte in the skbuff,
> recorded in skb_shinfo(skb)->tskey. When fragmenting skbuffs, ensure
> that the tskey is set for the fragment in which the tskey falls
> (seqno <= tskey < end_seqno).
>
> The original implementation did not address fragmentation in
> tcp_fragment or tso_fragment. Add code to inspect the sequence numbers
> and move both tskey and the relevant tx_flags if necessary.
>
> Reported-by: Eric Dumazet <eric.dumazet@...il.com>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
> ---
>  net/ipv4/tcp_output.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 8fcfc91..c07064e 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -1069,6 +1069,21 @@ static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int de
>         tcp_verify_left_out(tp);
>  }
>
> +static void tcp_fragment_tstamp(struct sk_buff *skb, struct sk_buff *skb2)
> +{
> +       struct skb_shared_info *shinfo = skb_shinfo(skb);
> +
> +       if (unlikely(shinfo->tx_flags & SKBTX_ANY_TSTAMP) &&
> +           after(shinfo->tskey, TCP_SKB_CB(skb)->end_seq)) {

This still has an off by one error, when tskey == end_seq. I will resubmit.

> +               struct skb_shared_info *shinfo2 = skb_shinfo(skb2);
> +               u8 tsflags = shinfo->tx_flags & SKBTX_ANY_TSTAMP;
> +
> +               shinfo->tx_flags &= ~tsflags;
> +               shinfo2->tx_flags |= tsflags;
> +               swap(shinfo->tskey, shinfo2->tskey);
> +       }
> +}
> +
>  /* Function to create two new TCP segments.  Shrinks the given segment
>   * to the specified size and appends a new segment with the rest of the
>   * packet to the list.  This won't be called frequently, I hope.
> @@ -1136,6 +1151,7 @@ int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
>          */
>         TCP_SKB_CB(buff)->when = TCP_SKB_CB(skb)->when;
>         buff->tstamp = skb->tstamp;
> +       tcp_fragment_tstamp(skb, buff);
>
>         old_factor = tcp_skb_pcount(skb);
>
> @@ -1652,6 +1668,7 @@ static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len,
>
>         buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
>         skb_split(skb, buff, len);
> +       tcp_fragment_tstamp(skb, buff);
>
>         /* Fix up tso_factor for both original and new SKB.  */
>         tcp_set_skb_tso_segs(sk, skb, mss_now);
> --
> 2.1.0.rc2.206.gedb03e5
>
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