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tcp: fix "old stuff" D-SACK causing SACK to be treated as D-SACK

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When we receive a D-SACK, where the sequence number satisfies:
	undo_marker <= start_seq < end_seq <= prior_snd_una
we consider this is a valid D-SACK and tcp_is_sackblock_valid()
returns true, then this D-SACK is discarded as "old stuff",
but the variable first_sack_index is not marked as negative
in tcp_sacktag_write_queue().

If this D-SACK also carries a SACK that needs to be processed
(for example, the previous SACK segment was lost), this SACK
will be treated as a D-SACK in the following processing of
tcp_sacktag_write_queue(), which will eventually lead to
incorrect updates of undo_retrans and reordering.

Fixes: fd6dad616d ("[TCP]: Earlier SACK block verification & simplify access to them")
Signed-off-by: Pengcheng Yang <yangpc@wangsu.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Pengcheng Yang 2019-12-30 17:54:41 +08:00 committed by David S. Miller
parent f7a48b68ab
commit c9655008e7
1 changed files with 4 additions and 1 deletions
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5
net/ipv4/tcp_input.c
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@ -1727,8 +1727,11 @@ tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
}
/* Ignore very old stuff early */
if (!after(sp[used_sacks].end_seq, prior_snd_una))
if (!after(sp[used_sacks].end_seq, prior_snd_una)) {
if (i == 0)
first_sack_index = -1;
continue;
}
used_sacks++;
}