[PATCH 3.16 163/245] pkt_sched: fq: do not accept silly TCA_FQ_QUANTUM

[Ben Hutchings]

3.16.83-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@xxxxxxxxxx>

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@xxxxxxxxxx>
Diagnosed-by: Florian Westphal <fw@xxxxxxxxx>
Reported-by: syzbot+dc9071cc5a85950bdfce@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[bwh: Backported to 3.16: Drop call to NL_SET_ERR_MSG_MOD() as extack is
 not supported.]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/net/sched/sch_fq.c
+++ b/net/sched/sch_fq.c
@@ -690,7 +690,7 @@ 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;