UBUNTU-CVE-2026-98427: Medium severity ubuntu/linux vulnerability

In the Linux kernel, the following vulnerability has been resolved: net/sched: codel: bound the dropping loop per dequeue call The CoDel control law schedules the next drop one interval/sqrt(count) after the previous drop, using the configured interval (codelparams.interval). For very small intervals the scheduled step rounds down to zero, so the dropping loop in codeldequeue() never advances and drains the entire backlog under the qdisc lock in one call - an unprivileged user can trigger a soft lockup this way. Fix in the shared codel code used by both codel and fqcodel: 1. Make the control-law step at least 1 tick so the dropping loop always moves forward. 2. Cap the dropping loop at CODELMAXDROPSPERDEQUEUE (256) drops per codeldequeue() call, resyncing dropnext to now when the cap is hit: the catch-up owed to the loop grows with the idle gap and the backlog, which no interval threshold can bound. This is a deliberate behaviour change after long idle gaps. The cap applies to fqcodel (4b549a2ef4be) and the mac80211 TXQ path (fixed interval, cap only). The target sojourn delay (codelparams.target) is not validated: it does not feed the control law, so a sub-tick value is aggressive rather than deadlock-prone. Conditions to recreate the bug: - tc qdisc add dev lo root handle 1: tbf rate 1kbit burst 2kb limit 1000000 - tc qdisc add dev lo parent 1:1 handle 10: codel interval 2us target 1ms noecn limit 1000000 (same for fqcodel) - unpatched kernel: tc accepts it; a UDP flood under the 1kbit tbf soft-lockups (watchdog: BUG: soft lockup) while one codeldequeue() call drops the backlog under the qdisc lock - patched kernel: same setup, at most 256 drops per dequeue call, no soft lockup Testing: claim reproducer and interval 2us/3us variants run clean; tdc qdisc category passes (see the selftests patch).