tcp: fix tcp_ofo_queue() to avoid including too much DUP SACK range

If the new coming segment covers more than one skbs in the ofo queue,
and which seq is equal to rcv_nxt , then the sequence range
that is not duplicated will be sent as DUP SACK,  the detail as below,
in step6, the {501,2001} range is clearly including too much
DUP SACK range:
1. client.43629 > server.8080: Flags [.], seq 501:1001, ack 1325288529,
win 20000, length 500: HTTP
2. server.8080 > client.43629: Flags [.], ack 1, win 65535, options
[nop,nop,TS val 269383721 ecr 200,nop,nop,sack 1 {501:1001}], length 0
3. Iclient.43629 > server.8080: Flags [.], seq 1501:2001,
ack 1325288529, win 20000, length 500: HTTP
4. server.8080 > client.43629: Flags [.], ack 1, win 65535, options
[nop,nop,TS val 269383721 ecr 200,nop,nop,sack 2 {1501:2001}
{501:1001}], length 0
5. client.43629 > server.8080: Flags [.], seq 1:2001,
ack 1325288529, win 20000, length 2000: HTTP
6. server.8080 > client.43629: Flags [.], ack 2001, win 65535,
options [nop,nop,TS val 269383722 ecr 200,nop,nop,sack 1 {501:2001}],
length 0

Signed-off-by: xin.guo <[email protected]>
Signed-off-by: NipaLocal <nipa@local>

Author: xin.guo

net/ipv4/tcp_input.c

@@ -4848,7 +4848,7 @@ static void tcp_ofo_queue(struct sock *sk)
 		if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
 			__u32 dsack = dsack_high;
 			if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
-				dsack_high = TCP_SKB_CB(skb)->end_seq;
+				dsack = TCP_SKB_CB(skb)->end_seq;
 			tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
 		}
 		p = rb_next(p);