1 files changed, 3 insertions, 2 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index eb7f82ebf4a3..65f6c0406245 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1222,7 +1222,7 @@ static int tcp_check_dsack(struct sock *sk, struct sk_buff *ack_skb,
         }
 
         /* D-SACK for already forgotten data... Do dumb counting. */
-        if (dup_sack &&
+        if (dup_sack && tp->undo_marker && tp->undo_retrans &&
             !after(end_seq_0, prior_snd_una) &&
             after(end_seq_0, tp->undo_marker))
                 tp->undo_retrans--;
@@ -1299,7 +1299,8 @@ static u8 tcp_sacktag_one(struct sk_buff *skb, struct sock *sk,
 
         /* Account D-SACK for retransmitted packet. */
         if (dup_sack && (sacked & TCPCB_RETRANS)) {
-                if (after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
+                if (tp->undo_marker && tp->undo_retrans &&
+                    after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
                         tp->undo_retrans--;
                 if (sacked & TCPCB_SACKED_ACKED)
                         state->reord = min(fack_count, state->reord);