net-timestamp: fix missing tcp fragmentation cases

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@gmail.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 17 insertions, 0 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 8fcfc91964ec..ef4a051de018 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) &&
+            !before(shinfo->tskey, TCP_SKB_CB(skb2)->seq)) {
+                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);