Bug 2559833 (CVE-2026-99040)

Summary:	CVE-2026-99040 kernel: KEYS: Fix add_key() race with keyring restriction
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 key management facility. This vulnerability allows a local user with write access to bypass security controls and add unauthorized keys to a restricted keyring. The issue occurs due to a race condition between key creation and the enforcement of keyring restrictions, allowing a key to be linked using an outdated restriction state.	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 2026-10-23 13:50:55 UTC

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

KEYS: Fix add_key() race with keyring restriction

__key_create_or_update() snapshots keyring->restrict_link before taking
the destination keyring's semaphore.  keyring_restrict() installs a
restriction while holding that semaphore.

This allows a writer to observe no restriction, wait for the keyring
owner to install a reject-all restriction and return successfully, and
then link a key using the stale NULL snapshot.  The writer only needs
write permission on the destination keyring.

Move the restrict_link read after __key_link_lock() and
__key_link_begin().  The read and the subsequent restriction check are
then serialized with restriction installation by keyring->sem.

The race was reproduced on v7.2.8 in 19 executions where restriction
installation returned before the link completed.  All 19 linked the key
despite the reject-all restriction.  With this change, 312 executions
reached the same ordering and every add_key() call failed with -EPERM.

The issue was found by manual concurrency analysis assisted by AI-based
analysis and independently verified with a QEMU reproducer and kernel
instrumentation.

Comment 1 gkamathe 2026-10-28 03:49:35 UTC

Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-99040.mbox