Bug 2521454 (CVE-2026-74590)

Summary:	CVE-2026-74590 kernel: fsverity: Fix bpf_get_fsverity_digest() dynptr assumptions
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
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Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in the Linux kernel's `fsverity` subsystem. A local attacker could exploit a race condition in the `bpf_get_fsverity_digest()` function by concurrently modifying its `digest_size` argument. This could lead to a system crash, resulting in a denial of service.	Story Points:	---
Clone Of:		Environment:
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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 2026-08-22 15:46:23 UTC

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

fsverity: Fix bpf_get_fsverity_digest() dynptr assumptions

The BPF verifier and the dynptr abstraction ensure that the memory space
referenced by a dynptr remains valid.  They do not, however, provide any
guarantee that the contents of the memory are stable.  kfuncs are
expected to remain memory-safe even if concurrent modifications occur.

bpf_get_fsverity_digest() didn't follow that: it could crash if
arg->digest_size was concurrently modified.

Fix that by using the known-good value hash_alg->digest_size instead.

Also widen 'dynptr_sz' and 'out_digest_sz' to u64 to match the return
type of __bpf_dynptr_size().  It doesn't appear that it can actually be
more than INT_MAX currently (since __bpf_dynptr_data_rw() excludes
file-based pointers), but the correct type might as well be used.

Comment 1 Keith Grant 2026-08-24 12:40:33 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026082212-CVE-2026-74590-5358@gregkh/T