netdev - [PATCH net-next 2/2] net_sched: sfq: always randomize hash perturbation

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Message-ID: <1325694181.2428.31.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
Date:	Wed, 04 Jan 2012 17:23:01 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>
Subject: [PATCH net-next 2/2] net_sched: sfq: always randomize hash
 perturbation

SFQ q->perturbation is used in sfq_hash() as an input to Jenkins hash.

We currently randomize this 32bit value only if a perturbation timer is
setup.

Its much better to always initialize it to defeat attackers, or else
they can predict very well what kind of packets they have to forge to
hit a particular flow.

Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
 net/sched/sch_sfq.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/net/sched/sch_sfq.c b/net/sched/sch_sfq.c
index 465af66..a1cb00e 100644
--- a/net/sched/sch_sfq.c
+++ b/net/sched/sch_sfq.c
@@ -591,12 +591,12 @@ static int sfq_init(struct Qdisc *sch, struct nlattr *opt)
 	q->cur_depth = 0;
 	q->tail = NULL;
 	q->divisor = SFQ_DEFAULT_HASH_DIVISOR;
-	if (opt == NULL) {
-		q->quantum = psched_mtu(qdisc_dev(sch));
-		q->scaled_quantum = SFQ_ALLOT_SIZE(q->quantum);
-		q->perturb_period = 0;
-		q->perturbation = net_random();
-	} else {
+	q->quantum = psched_mtu(qdisc_dev(sch));
+	q->scaled_quantum = SFQ_ALLOT_SIZE(q->quantum);
+	q->perturb_period = 0;
+	q->perturbation = net_random();
+
+	if (opt) {
 		int err = sfq_change(sch, opt);
 		if (err)
 			return err;


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