Bug 2540384 (CVE-2026-93795)

Summary:	CVE-2026-93795 kernel: blk-cgroup: fix leaks and online flag on radix_tree_insert failure
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
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 block control group (blk-cgroup) subsystem, which can lead to a Denial of Service (DoS). When an insertion failure occurs during the creation of a block group structure, the error-handling path fails to properly shut down reference counting. A local user can exploit this vulnerability to permanently leak memory and internal references, preventing affected control groups from being destroyed and exhausting system resources.	Story Points:	---
Clone Of:		Environment:
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Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-09-24 16:37:09 UTC

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

blk-cgroup: fix leaks and online flag on radix_tree_insert failure

When radix_tree_insert() fails in blkg_create(), the error path has two
issues:

1. blkg->online is set to true unconditionally, even when the blkg was
   never fully inserted.  Move the assignment inside the success block.

2. The error path calls blkg_put() without first calling
   percpu_ref_kill().  Because the refcount is still in percpu mode,
   percpu_ref_put() only does this_cpu_sub() without checking for zero,
   so blkg_release() is never triggered.  This permanently leaks the
   blkg memory, its percpu iostat, policy data, the parent blkg
   reference, and the cgroup css reference — the latter preventing the
   cgroup from ever being destroyed.

Fix by replacing blkg_put() with percpu_ref_kill(), matching the pattern
used in blkg_destroy().

Comment 1 Mauro Matteo Cascella 2026-09-28 11:31:50 UTC

Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-93795.mbox