Bug 2516883 (CVE-2026-74392)

Summary:	CVE-2026-74392 kernel: dm: limit target bio polling to one shot
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	rhel-process-autobot, 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 device mapper (dm) component. When io_uring with IOPOLL is used on a dm-stripe target, a task can enter a prolonged spinning poll loop. This can lead to an RCU (Read-Copy Update) CPU stall, causing 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 2026-08-15 06:38:27 UTC

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

dm: limit target bio polling to one shot

dm_poll_bio() is the ->poll_bio() callback for a stacked dm device.
The caller only knows about the dm queue, so it may decide to do a
spinning poll if it thinks a single queue is being polled. Passing those
flags unchanged to the mapped clone lets blk_mq_poll() spin on a target
queue from inside dm_poll_bio().

With io_uring IOPOLL on a dm-stripe target this can keep a task in

  dm_poll_bio() -> bio_poll() -> blk_mq_poll()

long enough to trigger an RCU CPU stall, before io_uring gets back to
io_iopoll_check() and its need_resched() check.

Keep dm's ->poll_bio() bounded by forcing one-shot polling for target
bios. The caller can invoke dm_poll_bio() again if it wants to keep
polling, and it also gets a chance to reap completions or reschedule
between passes.

Comment 1 Keith Grant 2026-08-20 20:27:35 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026081507-CVE-2026-74392-9f6b@gregkh/T