Bug 2532385 (CVE-2026-89674)

Summary: CVE-2026-89674 kernel: nfsd: fix XDR length calculation in nfsd4_ff_encode_layoutget
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: 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   
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A flaw was found in the `nfsd` component of the Linux kernel. Incorrect calculations in the XDR (External Data Representation) buffer size within the `nfsd4_ff_encode_layoutget()` function can lead to two critical issues. An attacker could potentially exploit this to write data beyond the intended memory boundaries, which might result in system instability or denial of service. Additionally, this flaw could cause the system to expose sensitive, uninitialized kernel memory to a client, leading to information disclosure.
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Description OSIDB Bzimport 2026-09-11 22:41:17 UTC 
In the Linux kernel, the following vulnerability has been resolved:

nfsd: fix XDR length calculation in nfsd4_ff_encode_layoutget

The XDR buffer size calculation in nfsd4_ff_encode_layoutget() has
multiple errors that can result in either an out-of-bounds write or
leaking uninitialized kernel memory to the client:

 - fh_len doesn't account for XDR padding on the file handle data
 - uid and gid lengths use "8 + len" but xdr_encode_opaque() actually
   writes "4 + xdr_align_size(len)" bytes
 - ds_len omits the flags and stats_collect_hint fields (8 bytes),
   while len's header constant overestimates by 8 bytes -- these
   partially cancel but leave a net mismatch

The worst case occurs with short strings (e.g. uid=0, gid=0 with an
odd-sized file handle), where the function writes up to 5 bytes past
the reserved XDR buffer. Conversely, when string lengths happen to be
4-byte aligned, the reservation is too large and stale buffer content
is sent to the client.

Fix this by breaking out every encoded field explicitly in the ds_len
calculation, using xdr_align_size() for all variable-length opaque
fields, and correcting the header constants.