This is a note to let you know that I've just added the patch titled
tcp: fix "old stuff" D-SACK causing SACK to be treated as D-SACK
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tcp-fix-old-stuff-d-sack-causing-sack-to-be-treated-as-d-sack.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Sat 11 Jan 2020 09:14:34 AM CET
From: Pengcheng Yang <yangpc@xxxxxxxxxx>
Date: Mon, 30 Dec 2019 17:54:41 +0800
Subject: tcp: fix "old stuff" D-SACK causing SACK to be treated as D-SACK
From: Pengcheng Yang <yangpc@xxxxxxxxxx>
[ 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 <yangpc@xxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/ipv4/tcp_input.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1716,8 +1716,11 @@ tcp_sacktag_write_queue(struct sock *sk,
}
/* 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++;
}
Patches currently in stable-queue which might be from yangpc@xxxxxxxxxx are
queue-4.19/tcp-fix-old-stuff-d-sack-causing-sack-to-be-treated-as-d-sack.patch
