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fq_codel: reject silly quantum parameters

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syzbot found that forcing a big quantum attribute would crash hosts fast,
essentially using this:

tc qd replace dev eth0 root fq_codel quantum 4294967295

This is because fq_codel_dequeue() would have to loop
~2^31 times in :

	if (flow->deficit <= 0) {
		flow->deficit += q->quantum;
		list_move_tail(&flow->flowchain, &q->old_flows);
		goto begin;
	}

SFQ max quantum is 2^19 (half a megabyte)
Lets adopt a max quantum of one megabyte for FQ_CODEL.

Fixes: 4b549a2ef4 ("fq_codel: Fair Queue Codel AQM")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2021-09-03 15:03:43 -07:00 • committed by David S. Miller
parent 10905b4a68
commit c7c5e6ff53
2 changed files with 12 additions and 2 deletions
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2
include/uapi/linux/pkt_sched.h
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@ -827,6 +827,8 @@ struct tc_codel_xstats {
/* FQ_CODEL */
#define FQ_CODEL_QUANTUM_MAX (1 << 20)
enum {
TCA_FQ_CODEL_UNSPEC,
TCA_FQ_CODEL_TARGET,