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

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[ Upstream commit a041f70e573e185d5d5fdbba53f0db2fbe7257ad ]

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 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, in violation of RFC 2883 rules.

1. client > server: Flags [.], seq 501:1001, ack 1325288529, win 20000, length 500
2. server > client: Flags [.], ack 1, [nop,nop,sack 1 {501:1001}], length 0
3. client > server: Flags [.], seq 1501:2001, ack 1325288529, win 20000, length 500
4. server > client: Flags [.], ack 1, [nop,nop,sack 2 {1501:2001} {501:1001}], length 0
5. client > server: Flags [.], seq 1:2001, ack 1325288529, win 20000, length 2000
6. server > client: Flags [.], ack 2001, [nop,nop,sack 1 {501:2001}], length 0

After this fix, the final ACK is as below:

6. server > client: Flags [.], ack 2001, options [nop,nop,sack 1 {501:1001}], length 0

[edumazet] added a new packetdrill test in the following patch.

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Signed-off-by: xin.guo <guoxin0309@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250626123420.1933835-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
xin.guo 2025-06-26 12:34:19 +00:00 • committed by Greg Kroah-Hartman
commit 2cbd59d0a6
1 changed files with 2 additions and 1 deletions
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3
net/ipv4/tcp_input.c
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@ -4588,8 +4588,9 @@ 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);