linux-kernel - [PATCH 3.12 34/94] tcp: fix tcp_match_skb_to_sack() for unaligned SACK at end of an skb

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <5f8c661beedfe757e0c56b415cbe6e2781892718.1406722270.git.jslaby@suse.cz>
Date:	Wed, 30 Jul 2014 14:14:23 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Neal Cardwell <ncardwell@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>,
	Ilpo Jarvinen <ilpo.jarvinen@...sinki.fi>,
	"David S. Miller" <davem@...emloft.net>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 34/94] tcp: fix tcp_match_skb_to_sack() for unaligned SACK at end of an skb

From: Neal Cardwell <ncardwell@...gle.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

[ 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@...gle.com>
Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
Cc: Eric Dumazet <edumazet@...gle.com>
Cc: Yuchung Cheng <ycheng@...gle.com>
Cc: Ilpo Jarvinen <ilpo.jarvinen@...sinki.fi>
Acked-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 net/ipv4/tcp_input.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 0e8af08a98fc..3c6ee41ba419 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1120,7 +1120,7 @@ static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
 			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;
-- 
2.0.1

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/