From 1c38487f46b243bfeefec0c0c86023a3904f2214 Mon Sep 17 00:00:00 2001 From: Jamal Hadi Salim Date: Tue, 1 Sep 2026 17:39:29 -0400 Subject: [PATCH] net/sched: ets: clamp quantum in parse and fallback paths MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit ets_qdisc_change() falls back to psched_mtu() with no floor for bands without an explicit quantum. With a crafted size table qdisc_pkt_len reaches ~2 GiB, so a zero psched_mtu on a headerless device makes the deficit-refill loop spin under the qdisc lock. Move the floor into ets_quantum_parse() so explicitly configured quanta are also clamped to [256, 1<<20], not just the fallback path. Conditions to recreate the bug: CONFIG_NET_SCH_ETS=y. Requires CAP_NET_ADMIN (namespace-local via unshare -Urn suffices). tc qdisc add dev dummy0 root ets bands 3 strict 2 quanta 1 1 Fixes: dcc68b4d8084 ("net: sch_ets: Add a new Qdisc") Reported-by: Vega Reviewed-by: Toke Høiland-Jørgensen Tested-by: Victor Nogueira Signed-off-by: Jamal Hadi Salim Link: https://patch.msgid.link/QDISC-0CFC.v3.20260901204856@mojatatu.com.9 Signed-off-by: Jakub Kicinski --- net/sched/sch_ets.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) diff --git a/net/sched/sch_ets.c b/net/sched/sch_ets.c index 25fcf4079fec..6cc902a03838 100644 --- a/net/sched/sch_ets.c +++ b/net/sched/sch_ets.c @@ -83,11 +83,7 @@ static int ets_quantum_parse(struct Qdisc *sch, const struct nlattr *attr, unsigned int *quantum, struct netlink_ext_ack *extack) { - *quantum = nla_get_u32(attr); - if (!*quantum) { - NL_SET_ERR_MSG(extack, "ETS quantum cannot be zero"); - return -EINVAL; - } + *quantum = clamp_t(u32, nla_get_u32(attr), 256, 1 << 20); return 0; } @@ -632,11 +628,13 @@ static int ets_qdisc_change(struct Qdisc *sch, struct nlattr *opt, return err; } /* If there are more bands than strict + quanta provided, the remaining - * ones are ETS with quantum of MTU. Initialize the missing values here. + * ones are ETS with quantum of max(MTU, 256). Initialize the missing + * values here. */ for (i = nstrict; i < nbands; i++) { if (!quanta[i]) - quanta[i] = psched_mtu(qdisc_dev(sch)); + quanta[i] = clamp_t(u32, (u32)psched_mtu(qdisc_dev(sch)), + 256, 1 << 20); } /* Before commit, make sure we can allocate all new qdiscs */