linux-kernel - [PATCH 3.2 102/131] tcp: Fix integer-overflow in TCP vegas

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Date:	Thu, 11 Sep 2014 13:32:13 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "David S. Miller" <davem@...emloft.net>,
	"Neal Cardwell" <ncardwell@...gle.com>,
	"Eric Dumazet" <eric.dumazet@...il.com>,
	"Doug Leith" <doug.leith@...m.ie>,
	"David Laight" <David.Laight@...LAB.COM>,
	"Stephen Hemminger" <stephen@...workplumber.org>,
	"Christoph Paasch" <christoph.paasch@...ouvain.be>
Subject: [PATCH 3.2 102/131] tcp: Fix integer-overflow in TCP vegas

3.2.63-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Christoph Paasch <christoph.paasch@...ouvain.be>

[ Upstream commit 1f74e613ded11517db90b2bd57e9464d9e0fb161 ]

In vegas we do a multiplication of the cwnd and the rtt. This
may overflow and thus their result is stored in a u64. However, we first
need to cast the cwnd so that actually 64-bit arithmetic is done.

Then, we need to do do_div to allow this to be used on 32-bit arches.

Cc: Stephen Hemminger <stephen@...workplumber.org>
Cc: Neal Cardwell <ncardwell@...gle.com>
Cc: Eric Dumazet <eric.dumazet@...il.com>
Cc: David Laight <David.Laight@...LAB.COM>
Cc: Doug Leith <doug.leith@...m.ie>
Fixes: 8d3a564da34e (tcp: tcp_vegas cong avoid fix)
Signed-off-by: Christoph Paasch <christoph.paasch@...ouvain.be>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/ipv4/tcp_vegas.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_vegas.c b/net/ipv4/tcp_vegas.c
index 80fa2bf..c042e52 100644
--- a/net/ipv4/tcp_vegas.c
+++ b/net/ipv4/tcp_vegas.c
@@ -218,7 +218,8 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
 			 * This is:
 			 *     (actual rate in segments) * baseRTT
 			 */
-			target_cwnd = tp->snd_cwnd * vegas->baseRTT / rtt;
+			target_cwnd = (u64)tp->snd_cwnd * vegas->baseRTT;
+			do_div(target_cwnd, rtt);
 
 			/* Calculate the difference between the window we had,
 			 * and the window we would like to have. This quantity

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