Jamal Hadi Salim says:
====================
net: sched: fix quantum/mtu overflow in fq, fq_codel, sch_codel, fq_pie, hhf, sfq
Several qdiscs derive their per-flow quantum or CoDel mtu from
psched_mtu() without an overflow or zero clamp, which can drive the
dequeue/credit-refill loop into a soft lockup or silently disable the
AQM. vega@nebusec.ai provided reports and PoCs for the following qdiscs:
sch_fq, sch_fq_codel, sch_fq_pie, sch_hhf, and sch_sfq.
sch_codel was found by inspection for the same pattern. It's TheLinuxWay
(i.e cutnpaste code from somewhere for your new feature) and the AIs
are having a lot of fun finding patterns. We must overcome!
Clamp the quantum (and, for the codel family, the cparams/params mtu)
to a sane range at init/change time so the dequeue loops terminate and
the AQM stays armed. The clamps live in the init/change paths, not the
per-packet fast path, so no hot-path cost is added for a configuration
issue.
This series depends on "net/sched: bound qdisc_pkt_len to prevent qdisc
soft lockup", which caps qdisc_pkt_len() at GSO_MAX_SIZE in
__qdisc_calculate_pkt_len(). That cap closes the fq_codel TCA_STAB
backlog-wrap vector (qdisc_pkt_len inflated to ~1 GiB wrapping the u32
per-flow backlog to 0 and NULL-derefing in fq_codel_drop()); with it
upstream this series no longer needs the fq_codel_drop() hardening hunk
that the earlier respin carried. The five quantum/mtu fixes here are
psched_mtu()-driven and orthogonal to the qdisc_pkt_len() cap.
Q: Why not bound the MTU at the source instead? dummy's max_mtu == 0 is
intentional (dev_validate_mtu() treats 0 as unbounded), other drivers
can legitimately advertise large MTUs, and qdiscs must not trust
psched_mtu() regardless.
Conditions to recreate the bug: a device whose MTU (plus
hard_header_len) wraps 2 * psched_mtu() or psched_mtu() into the sign
bit (e.g. a dummy device with max_mtu == 0 accepting a huge MTU).
Requires CAP_NET_ADMIN in a user namespace.
====================
Link: https://patch.msgid.link/20260822195509.112717-1-jhs@mojatatu.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
projects / linux / commitdiff