[PATCH 2/2] tcp: Increase TCP_MAXSEG socket option minimum CVE-2010-4165

[Paolo Pisati]

From: "David S. Miller" <davem at davemloft.net>

BugLink: http://bugs.launchpad.net/bugs/806374

commit upstream 7a1abd08d52fdeddb3e9a5a33f2f15cc6a5674d2

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.

CVE-2010-4165

Reported-by: Steve Chen <schen at mvista.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Paolo Pisati <paolo.pisati at canonical.com>
---
 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 4305154..4174f20 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1826,7 +1826,7 @@ 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;
 			break;
 		}
-- 
1.7.5.3