Bug 2507027 (CVE-2026-64326)

Summary:	CVE-2026-64326 kernel: block: skip sync_blockdev() on surprise removal in bdev_mark_dead()
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 block device handling. When a block device is unexpectedly removed, the `bdev_mark_dead()` function can unconditionally attempt to synchronize the device, even if it is no longer present. This can lead to a system hang, effectively causing a Denial of Service (DoS), as the system waits indefinitely for writeback operations that cannot complete. This vulnerability can be triggered by a local user or process interacting with block devices during surprise removal events.	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 2026-07-25 10:01:13 UTC

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

block: skip sync_blockdev() on surprise removal in bdev_mark_dead()

bdev_mark_dead()'s @surprise == true means the device is already gone.
The filesystem callback fs_bdev_mark_dead() honours this and skips
sync_filesystem(), but the bare block device path (no ->mark_dead op)
lost its !surprise guard when the holder ->mark_dead callback was wired
up (see Fixes), and now calls sync_blockdev() unconditionally, which can
hang forever waiting on writeback that can no longer complete.

syzkaller hit this via nvme_reset_work()'s "I/O queues lost" path:
nvme_mark_namespaces_dead() -> blk_mark_disk_dead() ->
bdev_mark_dead(bdev, true) -> sync_blockdev() blocks in
folio_wait_writeback(), wedging the reset worker and every task waiting
on it.

Skip the sync on surprise removal, matching fs_bdev_mark_dead();
invalidate_bdev() still runs. Orderly removal (surprise == false) is
unchanged.

Found by FuzzNvme(Syzkaller with FEMU fuzzing framework).

Comment 1 Mauro Matteo Cascella 2026-07-28 15:26:55 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026072512-CVE-2026-64326-8454@gregkh/T