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Bug#603158: possible kernel oops from user MSS

Package: linux-2.6
Version: 2.6.28-1
Severity: serious
Tags: security patch upstream

This bug was introduced in upstream version 2.6.28 and is about to be
fixed in 2.6.37.  I don't think any CVE has been assigned yet.


----- Forwarded message from David Miller <davem@davemloft.net> -----

From: David Miller <davem@davemloft.net>
To: shanwei@cn.fujitsu.com
Cc: schen@mvista.com, netdev@vger.kernel.org
Subject: Re: possible kernel oops from user MSS
Date: Thu, 11 Nov 2010 13:40:18 +0000

From: David Miller <davem@davemloft.net>
Date: Wed, 10 Nov 2010 21:33:13 -0800 (PST)

> I'll make the minimum 64 or something like that.

Here is the patch I will use:

tcp: Increase TCP_MAXSEG socket option minimum.

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

Fix this by increasing the minimum from 8 to 64.

Reported-by: Steve Chen <schen@mvista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
 net/ipv4/tcp.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 245603c..0814199 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2246,7 +2246,7 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
 		/* 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;

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----- End forwarded message -----

Ben Hutchings
We get into the habit of living before acquiring the habit of thinking.
                                                              - Albert Camus

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