Bug 2513405 (CVE-2026-68147)

Summary:	CVE-2026-68147 kernel: fscrypt: Avoid dynamic allocation in fscrypt_get_devices()
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:	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 fscrypt component. When a cryptographic key (blk_crypto_key) is being evicted, the system attempts to dynamically allocate memory. If this allocation fails, the key may be freed prematurely without proper eviction, leading to a use-after-free vulnerability. This could potentially allow a local attacker to cause a system crash or escalate privileges.	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 2026-08-10 12:35:31 UTC

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

fscrypt: Avoid dynamic allocation in fscrypt_get_devices()

When a blk_crypto_key starts being used or is evicted, fs/crypto/ calls
fscrypt_get_devices() to get the filesystem's list of block devices,
then iterates over them and calls blk_crypto_config_supported(),
blk_crypto_start_using_key(), or blk_crypto_evict_key() on each one.

Currently, the block device pointers are placed in a dynamically
allocated array.  This dynamic allocation is problematic because:

- It can fail, especially at the fscrypt_destroy_inline_crypt_key() call
  site when it's invoked for inode eviction under direct reclaim.

- fscrypt_destroy_inline_crypt_key() doesn't handle the failure.  It
  just zeroizes and frees the blk_crypto_key without calling
  blk_crypto_evict_key().  That causes a use-after-free.

For now, let's fix this in the straightforward and easily-backportable
way by switching to an on-stack array.  Currently the fscrypt
multi-device functionality is used only by f2fs, which has a hardcoded
limit of 8 block devices.  An on-stack array works fine for that.

(Of course, this solution won't scale up to large number of block
devices.  For that we'd need a different solution, like moving the block
device iteration into the filesystem.  Or in the case of btrfs, which
will only support blk-crypto-fallback, we should make it just call
blk-crypto-fallback directly, so the block devices won't be needed.)

Comment 1 gkamathe 2026-08-11 15:47:41 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026081001-CVE-2026-68147-8ad6@gregkh/T