[PATCH 3.13 007/187] tcp: Fix integer-overflow in TCP vegas

Kamal Mostafa kamal at canonical.com
Mon Sep 15 22:06:57 UTC 2014 -stable review patch.  If anyone has any objections, please let me know.


From: Christoph Paasch <christoph.paasch at uclouvain.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 at networkplumber.org>
Cc: Neal Cardwell <ncardwell at google.com>
Cc: Eric Dumazet <eric.dumazet at gmail.com>
Cc: David Laight <David.Laight at ACULAB.COM>
Cc: Doug Leith <doug.leith at nuim.ie>
Fixes: 8d3a564da34e (tcp: tcp_vegas cong avoid fix)
Signed-off-by: Christoph Paasch <christoph.paasch at uclouvain.be>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
 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 06cae62..6b1a5fd 100644
--- a/net/ipv4/tcp_vegas.c
+++ b/net/ipv4/tcp_vegas.c
@@ -219,7 +219,8 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 acked,
 			 * 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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