net/sched: fq: clamp quantum and initial_quantum in change path

The fq change path accepts TCA_FQ_QUANTUM in [1, INT_MAX] and
TCA_FQ_INITIAL_QUANTUM up to INT_MAX, while fq_init() already clamps to
[1, 1<<20]. A user can override the init clamp via tc qdisc change,
restoring the small-quantum deficit spin that the init clamp prevents.

Narrow iq_range.max to 1<<20 so TCA_FQ_INITIAL_QUANTUM is rejected at
parse time. Clamp TCA_FQ_QUANTUM to [256, 1<<20] in fq_change() and
fq_init() quantum to [256, 1<<20] for tiny-MTU devices.

Conditions to recreate the bug:
  CONFIG_NET_SCH_FQ=y. Requires CAP_NET_ADMIN (namespace-local via
  unshare -Urn suffices).

  tc qdisc add dev dummy0 root fq
  tc qdisc change dev dummy0 root fq quantum 1 stab data 32768 size_log 15 cell_log 0

Fixes: 709f34f7c28d ("net/sched: fq: add overflow bounds to quantum and initial quantum")
Reported-by: Vega <vega@nebusec.ai>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Tested-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://patch.msgid.link/QDISC-0CFC.v3.20260901204856@mojatatu.com.2
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions