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net/sched: pie: clamp psched_mtu in pie_drop_early

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pie_drop_early() calls psched_mtu() with no clamp. With mtu=0x80000000
the bytemode divide silently zeroes the drop probability, disabling AQM.
Clamp to [1, 1<<20].

Conditions to recreate the bug:
  CONFIG_NET_SCH_PIE=y. Requires CAP_NET_ADMIN (namespace-local via
  unshare -Urn suffices).

  tc qdisc add dev dummy0 root pie
  tc qdisc change dev dummy0 root pie stab data 32768 size_log 15 cell_log 0

Fixes: d4b36210c2 ("net: pkt_sched: PIE AQM scheme")
Reported-by: Vega <vega@nebusec.ai>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Tested-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/QDISC-0CFC.v3.20260901204856@mojatatu.com.7
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Jamal Hadi Salim 2026-09-01 17:39:27 -04:00 committed by Jakub Kicinski
parent 3c01f1ca5d
commit 54370e44c0
1 changed files with 1 additions and 1 deletions
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2
net/sched/sch_pie.c
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@ -35,7 +35,7 @@ bool pie_drop_early(struct Qdisc *sch, struct pie_params *params,
{
u64 rnd;
u64 local_prob = vars->prob;
u32 mtu = psched_mtu(qdisc_dev(sch));
u32 mtu = clamp_t(u32, psched_mtu(qdisc_dev(sch)), 1, 1 << 20);
/* If there is still burst allowance left skip random early drop */
if (vars->burst_time > 0)