[PATCH net v2 8/8] net/sched: ets: clamp quantum in parse and fallback paths
From: Jamal Hadi Salim <jhs@mojatatu.com>
Date: 2026-08-29 08:12:58
Also in:
stable
Subsystem:
networking [general], tc subsystem, the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Jamal Hadi Salim, Jiri Pirko, Linus Torvalds
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@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_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 */
--
2.43.0