[PATCH net v2 6/8] net/sched: pie: clamp psched_mtu in pie_drop_early

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: d4b36210c2e6 ("net: pkt_sched: PIE AQM scheme")
Reported-by: vega@nebusec.ai
Reviewed-by: Toke Høiland-Jørgensen <redacted>
Tested-by: Victor Nogueira <redacted>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: stable@vger.kernel.org
---
 net/sched/sch_pie.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sched/sch_pie.c b/net/sched/sch_pie.c
index b41f2def2e2c..3b7863ffd284 100644
--- a/net/sched/sch_pie.c
+++ b/net/sched/sch_pie.c

@@ -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)

-- 
2.43.0