sch_sfq: validate silly quantum values

[ Upstream commit df4953e4e997e273501339f607b77953772e3559 ]

syzbot managed to set up sfq so that q->scaled_quantum was zero,
triggering an infinite loop in sfq_dequeue()

More generally, we must only accept quantum between 1 and 2^18 - 7,
meaning scaled_quantum must be in [1, 0x7FFF] range.

Otherwise, we also could have a loop in sfq_dequeue()
if scaled_quantum happens to be 0x8000, since slot->allot
could indefinitely switch between 0 and 0x8000.

Fixes: eeaeb068f139 ("sch_sfq: allow big packets and be fair")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot+0251e883fe39e7a0cb0a@syzkaller.appspotmail.com
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/sched/sch_sfq.c b/net/sched/sch_sfq.c
index c787d4d..5a6def5 100644 (file)
--- a/net/sched/sch_sfq.c
+++ b/net/sched/sch_sfq.c
@@ -637,6 +637,15 @@ static int sfq_change(struct Qdisc *sch, struct nlattr *opt)
        if (ctl->divisor &&
            (!is_power_of_2(ctl->divisor) || ctl->divisor > 65536))
                return -EINVAL;
+
+       /* slot->allot is a short, make sure quantum is not too big. */
+       if (ctl->quantum) {
+               unsigned int scaled = SFQ_ALLOT_SIZE(ctl->quantum);
+
+               if (scaled <= 0 || scaled > SHRT_MAX)
+                       return -EINVAL;
+       }
+
        if (ctl_v1 && !red_check_params(ctl_v1->qth_min, ctl_v1->qth_max,
                                        ctl_v1->Wlog))
                return -EINVAL;