Bug 1224561 (CVE-2024-35985)

Summary:	VUL-0: CVE-2024-35985: kernel: sched/eevdf: Prevent vlag from going out of bounds in reweight_eevdf()
Product:	[Novell Products] SUSE Security Incidents	Reporter:	SMASH SMASH <smash_bz>
Component:	Incidents	Assignee:	Security Team bot <security-team>
Status:	RESOLVED FIXED	QA Contact:	Security Team bot <security-team>
Severity:	Normal
Priority:	P3 - Medium	CC:	gianluca.gabrielli, mkoutny
Version:	unspecified
Target Milestone:	---
Hardware:	Other
OS:	Other
URL:	https://smash.suse.de/issue/406714/
Whiteboard:
Found By:	Security Response Team	Services Priority:
Business Priority:		Blocker:	---
Marketing QA Status:	---	IT Deployment:	---

Description SMASH SMASH 2024-05-20 14:37:16 UTC

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

sched/eevdf: Prevent vlag from going out of bounds in reweight_eevdf()

It was possible to have pick_eevdf() return NULL, which then causes a
NULL-deref. This turned out to be due to entity_eligible() returning
falsely negative because of a s64 multiplcation overflow.

Specifically, reweight_eevdf() computes the vlag without considering
the limit placed upon vlag as update_entity_lag() does, and then the
scaling multiplication (remember that weight is 20bit fixed point) can
overflow. This then leads to the new vruntime being weird which then
causes the above entity_eligible() to go side-ways and claim nothing
is eligible.

Thus limit the range of vlag accordingly.

All this was quite rare, but fatal when it does happen.

References:
http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2024-35985
https://www.cve.org/CVERecord?id=CVE-2024-35985
https://git.kernel.org/stable/c/06f27e6d7bf0abf54488259ef36bbf0e1fccb35c
https://git.kernel.org/stable/c/1560d1f6eb6b398bddd80c16676776c0325fe5fe
https://git.kernel.org/stable/c/470d347b14b0ecffa9b39cf8f644fa2351db3efb
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2024/CVE-2024-35985.mbox

Comment 2 Andrea Mattiazzo 2024-06-07 12:11:51 UTC

All done, closing.