Bug 2540188 (CVE-2026-93216)

Summary:	CVE-2026-93216 kernel: mm/page_owner: use memcg_data snapshot to avoid TOCTOU in print_page_owner_memcg()
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. A Time-of-check to time-of-use (TOCTOU) vulnerability exists in the `print_page_owner_memcg()` function, where `page->memcg_data` is read multiple times without proper locking. If a memory page is concurrently freed and reallocated between these reads, it can trigger internal assertions, leading to a kernel crash. This can result in a Denial of Service (DoS) for the affected system.	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 2026-09-24 15:22:12 UTC

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

mm/page_owner: use memcg_data snapshot to avoid TOCTOU in print_page_owner_memcg()

print_page_owner_memcg() reads page->memcg_data via READ_ONCE() at the
start to guard against tail pages and NULL data.  However, it later
re-reads page->memcg_data locklessly in two places:

1: page_memcg_check(page)

2: PageMemcgKmem(page) (via folio_memcg_kmem(), which includes
   VM_BUG_ON assertions for tail pages and MEMCG_DATA_OBJEXTS)

If the page is concurrently freed and reallocated as a THP tail page or
slab page between these calls, the VM_BUG_ON assertions can trigger on
CONFIG_DEBUG_VM=y builds, crashing the kernel.

Fix both TOCTOU issues by using the memcg_data snapshot throughout.

Comment 1 Mauro Matteo Cascella 2026-09-25 09:12:46 UTC

Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-93216.mbox