[PATCH 3.15 11/26] tcp: Fix integer-overflow in TCP vegas

From: Greg Kroah-Hartman
Date: Fri Aug 08 2014 - 17:37:28 EST

3.15-stable review patch. If anyone has any objections, please let me know.


From: Christoph Paasch <christoph.paasch@xxxxxxxxxxxx>

[ 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@xxxxxxxxxxxxxxxxxx>
Cc: Neal Cardwell <ncardwell@xxxxxxxxxx>
Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Cc: David Laight <David.Laight@xxxxxxxxxx>
Cc: Doug Leith <doug.leith@xxxxxxx>
Fixes: 8d3a564da34e (tcp: tcp_vegas cong avoid fix)
Signed-off-by: Christoph Paasch <christoph.paasch@xxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/ipv4/tcp_vegas.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/ipv4/tcp_vegas.c
+++ b/net/ipv4/tcp_vegas.c
@@ -219,7 +219,8 @@ static void tcp_vegas_cong_avoid(struct
* 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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