This is a note to let you know that I've just added the patch titled
tcp: fix tcp_match_skb_to_sack() for unaligned SACK at end of an skb
to the 3.14-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-tcp_match_skb_to_sack-for-unaligned-sack-at-end-of-an-skb.patch
and it can be found in the queue-3.14 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 Jul 26 10:08:04 PDT 2014
From: Neal Cardwell <ncardwell@xxxxxxxxxx>
Date: Wed, 18 Jun 2014 21:15:03 -0400
Subject: tcp: fix tcp_match_skb_to_sack() for unaligned SACK at end of an skb
From: Neal Cardwell <ncardwell@xxxxxxxxxx>
[ Upstream commit 2cd0d743b05e87445c54ca124a9916f22f16742e ]
If there is an MSS change (or misbehaving receiver) that causes a SACK
to arrive that covers the end of an skb but is less than one MSS, then
tcp_match_skb_to_sack() was rounding up pkt_len to the full length of
the skb ("Round if necessary..."), then chopping all bytes off the skb
and creating a zero-byte skb in the write queue.
This was visible now because the recently simplified TLP logic in
bef1909ee3ed1c ("tcp: fixing TLP's FIN recovery") could find that 0-byte
skb at the end of the write queue, and now that we do not check that
skb's length we could send it as a TLP probe.
Consider the following example scenario:
mss: 1000
skb: seq: 0 end_seq: 4000 len: 4000
SACK: start_seq: 3999 end_seq: 4000
The tcp_match_skb_to_sack() code will compute:
in_sack = false
pkt_len = start_seq - TCP_SKB_CB(skb)->seq = 3999 - 0 = 3999
new_len = (pkt_len / mss) * mss = (3999/1000)*1000 = 3000
new_len += mss = 4000
Previously we would find the new_len > skb->len check failing, so we
would fall through and set pkt_len = new_len = 4000 and chop off
pkt_len of 4000 from the 4000-byte skb, leaving a 0-byte segment
afterward in the write queue.
With this new commit, we notice that the new new_len >= skb->len check
succeeds, so that we return without trying to fragment.
Fixes: adb92db857ee ("tcp: Make SACK code to split only at mss boundaries")
Reported-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Yuchung Cheng <ycheng@xxxxxxxxxx>
Cc: Ilpo Jarvinen <ilpo.jarvinen@xxxxxxxxxxx>
Acked-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 | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1169,7 +1169,7 @@ static int tcp_match_skb_to_sack(struct
unsigned int new_len = (pkt_len / mss) * mss;
if (!in_sack && new_len < pkt_len) {
new_len += mss;
- if (new_len > skb->len)
+ if (new_len >= skb->len)
return 0;
}
pkt_len = new_len;
Patches currently in stable-queue which might be from ncardwell@xxxxxxxxxx are
queue-3.14/tcp-fix-false-undo-corner-cases.patch
queue-3.14/tcp-fix-tcp_match_skb_to_sack-for-unaligned-sack-at-end-of-an-skb.patch
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