1 files changed, 22 insertions, 3 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 69d8c38ccd39..4d72781a49be 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1330,12 +1330,15 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
                 cached_fack_count = 0;
         }
 
-        for (i=0; i<num_sacks; i++, sp++) {
+        for (i = 0; i < num_sacks; i++) {
                 struct sk_buff *skb;
                 __u32 start_seq = ntohl(sp->start_seq);
                 __u32 end_seq = ntohl(sp->end_seq);
                 int fack_count;
                 int dup_sack = (found_dup_sack && (i == first_sack_index));
+                int next_dup = (found_dup_sack && (i+1 == first_sack_index));
+
+                sp++;
 
                 if (!tcp_is_sackblock_valid(tp, dup_sack, start_seq, end_seq)) {
                         if (dup_sack) {
@@ -1361,7 +1364,7 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
                         flag |= FLAG_DATA_LOST;
 
                 tcp_for_write_queue_from(skb, sk) {
-                        int in_sack;
+                        int in_sack = 0;
                         u8 sacked;
 
                         if (skb == tcp_send_head(sk))
@@ -1380,7 +1383,23 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
                         if (!before(TCP_SKB_CB(skb)->seq, end_seq))
                                 break;
 
-                        in_sack = tcp_match_skb_to_sack(sk, skb, start_seq, end_seq);
+                        dup_sack = (found_dup_sack && (i == first_sack_index));
+
+                        /* Due to sorting DSACK may reside within this SACK block! */
+                        if (next_dup) {
+                                u32 dup_start = ntohl(sp->start_seq);
+                                u32 dup_end = ntohl(sp->end_seq);
+
+                                if (before(TCP_SKB_CB(skb)->seq, dup_end)) {
+                                        in_sack = tcp_match_skb_to_sack(sk, skb, dup_start, dup_end);
+                                        if (in_sack > 0)
+                                                dup_sack = 1;
+                                }
+                        }
+
+                        /* DSACK info lost if out-of-mem, try SACK still */
+                        if (in_sack <= 0)
+                                in_sack = tcp_match_skb_to_sack(sk, skb, start_seq, end_seq);
                         if (in_sack < 0)
                                 break;