1 files changed, 36 insertions, 20 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 0aa17243d369..5187870d0333 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -960,6 +960,39 @@ static void tcp_update_reordering(struct sock *sk, const int metric,
  * Both of these heuristics are not used in Loss state, when we cannot
  * account for retransmits accurately.
  */
+static int tcp_check_dsack(struct tcp_sock *tp, struct sk_buff *ack_skb,
+                           struct tcp_sack_block_wire *sp, int num_sacks,
+                           u32 prior_snd_una)
+{
+        u32 start_seq_0 = ntohl(get_unaligned(&sp[0].start_seq));
+        u32 end_seq_0 = ntohl(get_unaligned(&sp[0].end_seq));
+        int dup_sack = 0;
+
+        if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
+                dup_sack = 1;
+                tp->rx_opt.sack_ok |= 4;
+                NET_INC_STATS_BH(LINUX_MIB_TCPDSACKRECV);
+        } else if (num_sacks > 1) {
+                u32 end_seq_1 = ntohl(get_unaligned(&sp[1].end_seq));
+                u32 start_seq_1 = ntohl(get_unaligned(&sp[1].start_seq));
+
+                if (!after(end_seq_0, end_seq_1) &&
+                    !before(start_seq_0, start_seq_1)) {
+                        dup_sack = 1;
+                        tp->rx_opt.sack_ok |= 4;
+                        NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFORECV);
+                }
+        }
+
+        /* D-SACK for already forgotten data... Do dumb counting. */
+        if (dup_sack &&
+            !after(end_seq_0, prior_snd_una) &&
+            after(end_seq_0, tp->undo_marker))
+                tp->undo_retrans--;
+
+        return dup_sack;
+}
+
 static int
 tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_una)
 {
@@ -985,27 +1018,10 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
         }
         prior_fackets = tp->fackets_out;
 
-        /* Check for D-SACK. */
-        if (before(ntohl(sp[0].start_seq), TCP_SKB_CB(ack_skb)->ack_seq)) {
-                flag |= FLAG_DSACKING_ACK;
-                found_dup_sack = 1;
-                tp->rx_opt.sack_ok |= 4;
-                NET_INC_STATS_BH(LINUX_MIB_TCPDSACKRECV);
-        } else if (num_sacks > 1 &&
-                        !after(ntohl(sp[0].end_seq), ntohl(sp[1].end_seq)) &&
-                        !before(ntohl(sp[0].start_seq), ntohl(sp[1].start_seq))) {
+        found_dup_sack = tcp_check_dsack(tp, ack_skb, sp,
+                                         num_sacks, prior_snd_una);
+        if (found_dup_sack)
                 flag |= FLAG_DSACKING_ACK;
-                found_dup_sack = 1;
-                tp->rx_opt.sack_ok |= 4;
-                NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFORECV);
-        }
-
-        /* D-SACK for already forgotten data...
-         * Do dumb counting. */
-        if (found_dup_sack &&
-                        !after(ntohl(sp[0].end_seq), prior_snd_una) &&
-                        after(ntohl(sp[0].end_seq), tp->undo_marker))
-                tp->undo_retrans--;
 
         /* Eliminate too old ACKs, but take into
          * account more or less fresh ones, they can