[PATCH RESUBMIT net] tcp: Fix integer-overflows in TCP veno

[PATCH RESUBMIT net] tcp: Fix integer-overflows in TCP veno

[Christoph Paasch]

In veno 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.

A first attempt at fixing 76f1017757aa0 ([TCP]: TCP Veno congestion
control) was made by 159131149c2 (tcp: Overflow bug in Vegas), but it
failed to add the required cast in tcp_veno_cong_avoid().

Fixes: 76f1017757aa0 ([TCP]: TCP Veno congestion control)
Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>
---

Notes:
    Resubmit as requested by David.

 net/ipv4/tcp_veno.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_veno.c b/net/ipv4/tcp_veno.c
index 27b9825753d1..8276977d2c85 100644
--- a/net/ipv4/tcp_veno.c
+++ b/net/ipv4/tcp_veno.c
@@ -144,7 +144,7 @@ static void tcp_veno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 
 		rtt = veno->minrtt;
 
-		target_cwnd = (tp->snd_cwnd * veno->basertt);
+		target_cwnd = (u64)tp->snd_cwnd * veno->basertt;
 		target_cwnd <<= V_PARAM_SHIFT;
 		do_div(target_cwnd, rtt);
 
-- 
1.9.3

Re: [PATCH RESUBMIT net] tcp: Fix integer-overflows in TCP veno

[David Miller]

From: Christoph Paasch <christoph.paasch@uclouvain.be>
Date: Tue, 29 Jul 2014 12:07:27 +0200

> In veno 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.
> 
> A first attempt at fixing 76f1017757aa0 ([TCP]: TCP Veno congestion
> control) was made by 159131149c2 (tcp: Overflow bug in Vegas), but it
> failed to add the required cast in tcp_veno_cong_avoid().
> 
> Fixes: 76f1017757aa0 ([TCP]: TCP Veno congestion control)
> Signed-off-by: Christoph Paasch <christoph.paasch@uclouvain.be>

Applied and queued up for -stable.