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 a985588695dfdcfaaca0a801192e35cf2efddba1..1a0f943a3423c8add1f089f9d545bf1aecb3253d 100644 (file)
--- 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;