From: Eric Dumazet <edumazet@google.com>
Date: Mon, 6 Jan 2020 06:10:39 -0800
Subject: pkt_sched: fq: do not accept silly TCA_FQ_QUANTUM
Git-commit: d9e15a2733067c9328fb56d98fe8e574fa19ec31
Patch-mainline: 5.5-rc6
References: networking-stable-20_01_11

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.

[js] no extack in 4.12 yet.

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>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 net/sched/sch_fq.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/sched/sch_fq.c
+++ b/net/sched/sch_fq.c
@@ -734,7 +734,7 @@ static int fq_change(struct Qdisc *sch,
 	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;