Bug 2541248 (CVE-2026-98012)

Summary:	CVE-2026-98012 kernel: net/sched: sfq: clamp quantum in change path
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	low	Docs Contact:
Priority:	low
Version:	unspecified	CC:	akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in the Linux kernel's Stochastic Fairness Queueing (SFQ) network packet scheduling subsystem. A local attacker with network administration privileges, including within an unprivileged user namespace, can supply an improperly bounded quantum parameter alongside a crafted packet size table. This can trigger an excessively long execution loop while holding an internal lock, leading to a system lockup and a Denial of Service (DoS).	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-09-25 11:09:59 UTC

In the Linux kernel, the following vulnerability has been resolved:

net/sched: sfq: clamp quantum in change path

sfq_change() accepts any non-negative quantum (only rejects
(int)ctl->quantum < 0). With a crafted size table qdisc_pkt_len reaches
~2 GiB, so quantum=1 makes the deficit-refill loop spin ~2^31 times
under the qdisc lock (a soft lockup / denial of service).

Add max(256U, ...) matching fq_codel_change(). Reject quantum > 1<<20
with -EINVAL, matching fq_codel_change() and the init clamp.

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

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

Comment 1 Keith Grant 2026-09-28 19:43:19 UTC

Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-98012.mbox