linux-kernel - [PATCH 046/173] tcp: Increase TCP

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Date:	Mon, 25 Apr 2011 22:03:18 +0200
From:	Willy Tarreau <w@....eu>
To:	linux-kernel@...r.kernel.org, stable@...nel.org,
	stable-review@...nel.org
Cc:	"David S. Miller" <davem@...emloft.net>,
	Moritz Muehlenhoff <jmm@...ian.org>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: [PATCH 046/173] tcp: Increase TCP_MAXSEG socket option minimum.

2.6.27.59-stable review patch.  If anyone has any objections, please let us know.

------------------

From: David S. Miller <davem@...emloft.net>

commit 7a1abd08d52fdeddb3e9a5a33f2f15cc6a5674d2 upstream.

As noted by Steve Chen, since commit
f5fff5dc8a7a3f395b0525c02ba92c95d42b7390 ("tcp: advertise MSS
requested by user") we can end up with a situation where
tcp_select_initial_window() does a divide by a zero (or
even negative) mss value.

The problem is that sometimes we effectively subtract
TCPOLEN_TSTAMP_ALIGNED and/or TCPOLEN_MD5SIG_ALIGNED from the mss.

Fix this by increasing the minimum from 8 to 64.

Reported-by: Steve Chen <schen@...sta.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Cc: Moritz Muehlenhoff <jmm@...ian.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 net/ipv4/tcp.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2117,7 +2117,7 @@ static int do_tcp_setsockopt(struct sock
 		/* Values greater than interface MTU won't take effect. However
 		 * at the point when this call is done we typically don't yet
 		 * know which interface is going to be used */
-		if (val < 8 || val > MAX_TCP_WINDOW) {
+		if (val < 64 || val > MAX_TCP_WINDOW) {
 			err = -EINVAL;
 			break;
 		}

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