linux-kernel - [ 24/48] tcp: Fix integer-overflow in TCP vegas

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Message-Id: <20141116215329.653149999@1wt.eu>
Date:	Sun, 16 Nov 2014 22:53:52 +0100
From:	Willy Tarreau <w@....eu>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Stephen Hemminger <stephen@...workplumber.org>,
	Neal Cardwell <ncardwell@...gle.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	David Laight <David.Laight@...LAB.COM>,
	Doug Leith <doug.leith@...m.ie>,
	Christoph Paasch <christoph.paasch@...ouvain.be>,
	"David S. Miller" <davem@...emloft.net>, Willy Tarreau <w@....eu>
Subject: [ 24/48] tcp: Fix integer-overflow in TCP vegas

2.6.32-longterm 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: Willy Tarreau <w@....eu>
---
 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 c6743ee..3044e40 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
-- 
1.7.12.2.21.g234cd45.dirty



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