Loop with Unreachable Exit Condition ('Infinite Loop') Affecting bpftool package, versions *
Threat Intelligence
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Test your applications- Snyk IDSNYK-CENTOS7-BPFTOOL-21097404
- published16 Oct 2026
- disclosed14 Oct 2026
Introduced: 14 Oct 2026
NewCVE-2026-98427 (opens in a new tab)How to fix?
There is no fixed version for Centos:7 bpftool.
NVD Description
Note: Versions mentioned in the description apply only to the upstream bpftool package and not the bpftool package as distributed by Centos.
See How to fix? for Centos:7 relevant fixed versions and status.
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 (codel_params.interval). For very small intervals the scheduled step rounds down to zero, so the dropping loop in codel_dequeue() 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 fq_codel:
Make the control-law step at least 1 tick so the dropping loop always moves forward.
Cap the dropping loop at CODEL_MAX_DROPS_PER_DEQUEUE (256) drops per codel_dequeue() call, resyncing drop_next 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 fq_codel (4b549a2ef4be) and the mac80211 TXQ path (fixed interval, cap only).
The target sojourn delay (codel_params.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 fq_codel)
- unpatched kernel: tc accepts it; a UDP flood under the 1kbit tbf soft-lockups (watchdog: BUG: soft lockup) while one codel_dequeue() 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).