tcp: Overflow bug in Vegas
From: Lachlan Andrew <lachlan.andrew@gmail.com>
There is an overflow bug in net/ipv4/tcp_vegas.c for large BDPs
(e.g. 400Mbit/s, 400ms). The multiplication (old_wnd *
vegas->baseRTT) << V_PARAM_SHIFT overflows a u32.
[ Fix tcp_veno.c too, it has similar calculations. -DaveM ]
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_vegas.c b/net/ipv4/tcp_vegas.c
index be24d6e..0e1a8c9 100644
--- a/net/ipv4/tcp_vegas.c
+++ b/net/ipv4/tcp_vegas.c
@@ -229,7 +229,8 @@
*/
tcp_reno_cong_avoid(sk, ack, in_flight);
} else {
- u32 rtt, target_cwnd, diff;
+ u32 rtt, diff;
+ u64 target_cwnd;
/* We have enough RTT samples, so, using the Vegas
* algorithm, we determine if we should increase or
@@ -252,8 +253,9 @@
* We keep it as a fixed point number with
* V_PARAM_SHIFT bits to the right of the binary point.
*/
- target_cwnd = ((old_wnd * vegas->baseRTT)
- << V_PARAM_SHIFT) / rtt;
+ target_cwnd = ((u64)old_wnd * vegas->baseRTT);
+ target_cwnd <<= V_PARAM_SHIFT;
+ do_div(target_cwnd, rtt);
/* Calculate the difference between the window we had,
* and the window we would like to have. This quantity
@@ -279,7 +281,7 @@
* utilization.
*/
tp->snd_cwnd = min(tp->snd_cwnd,
- (target_cwnd >>
+ ((u32)target_cwnd >>
V_PARAM_SHIFT)+1);
} else if (tp->snd_cwnd <= tp->snd_ssthresh) {
diff --git a/net/ipv4/tcp_veno.c b/net/ipv4/tcp_veno.c
index d16689e..2bf618a 100644
--- a/net/ipv4/tcp_veno.c
+++ b/net/ipv4/tcp_veno.c
@@ -133,7 +133,8 @@
*/
tcp_reno_cong_avoid(sk, ack, in_flight);
} else {
- u32 rtt, target_cwnd;
+ u64 target_cwnd;
+ u32 rtt;
/* We have enough rtt samples, so, using the Veno
* algorithm, we determine the state of the network.
@@ -141,8 +142,9 @@
rtt = veno->minrtt;
- target_cwnd = ((tp->snd_cwnd * veno->basertt)
- << V_PARAM_SHIFT) / rtt;
+ target_cwnd = (tp->snd_cwnd * veno->basertt);
+ target_cwnd <<= V_PARAM_SHIFT;
+ do_div(target_cwnd, rtt);
veno->diff = (tp->snd_cwnd << V_PARAM_SHIFT) - target_cwnd;