Bug 2528691 (CVE-2026-80859)

Summary:	CVE-2026-80859 kernel: fuse: fix missing barrier when checking io-uring readiness
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 FUSE (Filesystem in Userspace) subsystem. A missing memory barrier when checking the readiness of io-uring queues could allow a CPU to observe an inconsistent state. This inconsistency can bypass a critical check, potentially reintroducing a lock-order inversion deadlock. Such a deadlock could lead to a system hang or 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 2026-09-04 16:24:17 UTC

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

fuse: fix missing barrier when checking io-uring readiness

fuse_block_alloc() reads fch->initialized and then fch->io_uring.
fch->io_uring is set before fch->initialized, ordered by the smp_wmb()
in fuse_chan_set_intialized(), but fuse_block_alloc() has no matching
read barrier between the two loads.

This may lead a CPU to observe fch->initialized=1 but fch->io_uring=0,
and skip the check that blocks request allocation until the io-uring
queues are ready. This can reintroduce the lock-order inversion deadlock
that commit 3393ff964e0f prevents.

Add an smp_rmb() barrier to pair with the smp_wmb() in
fuse_chan_set_initialized() to prevent this.

Comment 1 gkamathe 2026-09-08 13:14:37 UTC

Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-80859.mbox