Bug 2536739 (CVE-2026-93084)

Summary:	CVE-2026-93084 kernel: firmware: arm_scmi: Drop handle on protocol bind failures
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
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 arm_scmi firmware. When the SCMI bus notifier acquires a handle, but the device link cannot be properly established or a protocol driver probe fails, the SCMI instance's reference count may not be correctly released. This can lead to a resource leak. Furthermore, a concurrent parent unbind operation could tear down the SCMI instance while a child still holds a handle, potentially causing system instability or a denial of service.	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 2026-09-17 19:23:50 UTC

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

firmware: arm_scmi: Drop handle on protocol bind failures

The SCMI bus notifier acquires an SCMI handle when the driver core emits
BUS_NOTIFY_BIND_DRIVER, before invoking the protocol driver probe
callback. The protocol probe path only checks whether sdev->handle is
set.

If device_link_add() fails after the handle has been acquired, the
protocol device can still bind with a valid handle but without the
dependency link to the SCMI parent. A concurrent parent unbind can then
miss the child and tear down the SCMI instance while the child still
holds a handle into it.

If the protocol driver probe later fails, for example with
-EPROBE_DEFER, the driver core emits BUS_NOTIFY_DRIVER_NOT_BOUND rather
than BUS_NOTIFY_UNBOUND_DRIVER. The SCMI notifier only released the
handle on BUS_NOTIFY_UNBOUND_DRIVER, so each failed protocol-device bind
leaked the SCMI instance users refcount and left sdev->handle set after
the failed probe.

Make the link helper report failure and drop the acquired handle if the
link cannot be created. Also handle BUS_NOTIFY_DRIVER_NOT_BOUND in the
same cleanup path used for unbind so failed probes balance the earlier
BUS_NOTIFY_BIND_DRIVER acquisition.

Comment 1 gkamathe 2026-09-19 02:51:21 UTC

Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-93084.mbox