tcp: Make SACK code to split only at mss boundaries

Sadly enough, this adds possible divide though we try to avoid
it by checking one mss as common case.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 23 insertions, 4 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 3f26599ddc88..ca46eb9151f8 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1248,20 +1248,39 @@ static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
 {
         int in_sack, err;
         unsigned int pkt_len;
+        unsigned int mss;
 
         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
                   !before(end_seq, TCP_SKB_CB(skb)->end_seq);
 
         if (tcp_skb_pcount(skb) > 1 && !in_sack &&
             after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
-
+                mss = tcp_skb_mss(skb);
                 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
 
-                if (!in_sack)
+                if (!in_sack) {
                         pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
-                else
+                        if (pkt_len < mss)
+                                pkt_len = mss;
+                } else {
                         pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
-                err = tcp_fragment(sk, skb, pkt_len, skb_shinfo(skb)->gso_size);
+                        if (pkt_len < mss)
+                                return -EINVAL;
+                }
+
+                /* Round if necessary so that SACKs cover only full MSSes
+                 * and/or the remaining small portion (if present)
+                 */
+                if (pkt_len > mss) {
+                        unsigned int new_len = (pkt_len / mss) * mss;
+                        if (!in_sack && new_len < pkt_len) {
+                                new_len += mss;
+                                if (new_len > skb->len)
+                                        return 0;
+                        }
+                        pkt_len = new_len;
+                }
+                err = tcp_fragment(sk, skb, pkt_len, mss);
                 if (err < 0)
                         return err;
         }