drr_change_class() rejects explicit quantum==0 but falls back to psched_mtu() with no floor. With a crafted size table qdisc_pkt_len reaches ~2 GiB, so quantum=1 (or a zero psched_mtu on a headerless device) makes the deficit-refill loop spin under the qdisc lock. Add clamp_t(u32, quantum, 256, 1<<20) after the zero reject and on the fallback path. The explicit-zero reject is preserved. Conditions to recreate the bug: CONFIG_NET_SCH_DRR=y. Requires CAP_NET_ADMIN (namespace-local via unshare -Urn suffices). tc qdisc add dev dummy0 root drr tc class add dev dummy0 parent 1: classid 1:1 drr quantum 1 Fixes: 13d2a1d2b032 ("pkt_sched: add DRR scheduler") Reported-by: vega@nebusec.ai Reviewed-by: Toke Høiland-Jørgensen Tested-by: Victor Nogueira Signed-off-by: Jamal Hadi Salim Cc: stable@vger.kernel.org --- net/sched/sch_drr.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/sched/sch_drr.c b/net/sched/sch_drr.c index 91b1ef824afa..8621d057edd9 100644 --- a/net/sched/sch_drr.c +++ b/net/sched/sch_drr.c @@ -82,8 +82,9 @@ static int drr_change_class(struct Qdisc *sch, u32 classid, u32 parentid, NL_SET_ERR_MSG(extack, "Specified DRR quantum cannot be zero"); return -EINVAL; } + quantum = clamp_t(u32, quantum, 256, 1 << 20); } else - quantum = psched_mtu(qdisc_dev(sch)); + quantum = clamp_t(u32, (u32)psched_mtu(qdisc_dev(sch)), 256, 1 << 20); if (cl != NULL) { if (tca[TCA_RATE]) { -- 2.43.0