From: Pengcheng Yang Date: Mon, 30 Dec 2019 09:54:41 +0000 (+0800) Subject: tcp: fix "old stuff" D-SACK causing SACK to be treated as D-SACK X-Git-Tag: v4.19.95~10 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=5ea5b6e3c6e146efeae7df6b0da898868cdb4765;p=thirdparty%2Fkernel%2Fstable.git tcp: fix "old stuff" D-SACK causing SACK to be treated as D-SACK [ Upstream commit c9655008e7845bcfdaac10a1ed8554ec167aea88 ] 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: fd6dad616d4f ("[TCP]: Earlier SACK block verification & simplify access to them") Signed-off-by: Pengcheng Yang Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 3a08ee81cbc3b..578b65e6e65b8 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -1716,8 +1716,11 @@ 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++; }