Bug 2532419 (CVE-2026-89677)

Summary:	CVE-2026-89677 kernel: nfsd: fix possible fh_compose of wrong dentry in nfsd4_create_file()
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:	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:
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Doc Text:	A flaw was found in the Linux kernel's Network File System Daemon (nfsd). When creating files, the `dentry_create()` function could return an unexpected directory entry (dentry). This could lead to a previously stored dentry being prematurely freed and then used again, potentially causing memory corruption or a denial of service (DoS) due to an invalid memory access.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
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Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-09-11 22:55:12 UTC

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

nfsd: fix possible fh_compose of wrong dentry in nfsd4_create_file()

dentry_create() can hypothetically provide a different dentry than the
one passed in.  This could happen, for example, if the exported
filesystem is NFS, and the server returned to OPEN a filehandle which
matched a directory that was already in the dcache.  Clearly this would
not be expected!

If this were to happen the dentry (child) that was already stored in
resfhp could be freed and later dereferenced.

We shouldn't call fh_compose() until we are certain that we have the
final dentry, so this patch moved the fh_compose() call to two places:
one for the case where the target already exists, and one after
dentry_create() where it was created.

Comment 1 gkamathe 2026-09-15 09:39:34 UTC

Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89677.mbox