From: Eric Dumazet <edumazet@google.com>
Date: Mon, 6 Jan 2020 14:10:39 +0000 (-0800)
Subject: pkt_sched: fq: do not accept silly TCA_FQ_QUANTUM
X-Git-Tag: v3.16.83~85
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2641f299648d5cc35eec3d4daa7b586203d3f5bb;p=thirdparty%2Fkernel%2Fstable.git

pkt_sched: fq: do not accept silly TCA_FQ_QUANTUM

commit d9e15a2733067c9328fb56d98fe8e574fa19ec31 upstream.

As diagnosed by Florian :

If TCA_FQ_QUANTUM is set to 0x80000000, fq_deueue()
can loop forever in :

if (f->credit <= 0) {
  f->credit += q->quantum;
  goto begin;
}

... because f->credit is either 0 or -2147483648.

Let's limit TCA_FQ_QUANTUM to no more than 1 << 20 :
This max value should limit risks of breaking user setups
while fixing this bug.

Fixes: afe4fd062416 ("pkt_sched: fq: Fair Queue packet scheduler")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Diagnosed-by: Florian Westphal <fw@strlen.de>
Reported-by: syzbot+dc9071cc5a85950bdfce@syzkaller.appspotmail.com
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16: Drop call to NL_SET_ERR_MSG_MOD() as extack is
 not supported.]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

diff --git a/net/sched/sch_fq.c b/net/sched/sch_fq.c
index a985588695dfd..1a0f943a3423c 100644
--- a/net/sched/sch_fq.c
+++ b/net/sched/sch_fq.c
@@ -690,7 +690,7 @@ static int fq_change(struct Qdisc *sch, struct nlattr *opt)
 	if (tb[TCA_FQ_QUANTUM]) {
 		u32 quantum = nla_get_u32(tb[TCA_FQ_QUANTUM]);
 
-		if (quantum > 0)
+		if (quantum > 0 && quantum <= (1 << 20))
 			q->quantum = quantum;
 		else
 			err = -EINVAL;