nfsd: reject out-of-range useconds in NFSv2 SETATTR/CREATE

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Summary

CVECVE-2026-89665
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-11 20:19:52 UTC
Updated2026-09-11 20:19:52 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: nfsd: reject out-of-range useconds in NFSv2 SETATTR/CREATE The NFSv2 sattr decoder converts the wire useconds to nanoseconds in svcxdr_decode_sattr(): iap->ia_atime.tv_nsec = tmp2 * NSEC_PER_USEC; tmp2 is a u32 and NSEC_PER_USEC is 1000, so the product is computed in unsigned long. On ILP32 that is 32 bits, and an out-of-range useconds value such as 4294968 wraps to tv_nsec == 704. The corruption therefore happens during decode, before any proc function can inspect the value, and a later range check on tv_nsec would see an in-range result and accept it. Rejecting in the decoder yields an RPC GARBAGE_ARGS reply. NFSv2 defines no NFSERR_INVAL, so there is no NFS-level status to return for a malformed time argument, and the check cannot move to the proc function the way the v3/v4 nsec range checks do. Guard the raw useconds before the multiplication and reject values greater than 1000000. useconds == 1000000 is kept: it is the Sun convention for "set to the current server time", and the in-tree Linux NFSv2 client emits it in both the atime and the mtime field for a plain touch / utimes(file, NULL) (see encode_sattr() and xdr_encode_current_server_time() in fs/nfs/nfs2xdr.c). Rejecting 1000000 would turn that common operation into a hard decode failure for both SETATTR and CREATE. 1000000 * NSEC_PER_USEC is 10^9, which does not wrap on ILP32, so the Sun convention value passes through safely. Only genuinely out-of-range values (> 1000000) are rejected. The atime and mtime guards are therefore symmetric. The decoder only applied the Sun convention in the mtime block, which clears ATTR_ATIME_SET|ATTR_MTIME_SET when mtime useconds == 1000000. If a client puts 1000000 in the atime field but not in the mtime field, the atime block stored an out-of-range tv_nsec (10^9) and left ATTR_ATIME_SET set, so the bogus value reached the filesystem. Apply the convention in the atime block as well, clearing ATTR_ATIME_SET so the server uses its current time and ignores the value. Only ATTR_ATIME_SET is cleared there. The mtime block keeps its existing behavior, where 1000000 means "set both atime and mtime to now". [ cel: various tweaks, addenda, and clean-ups ]

Risk And Classification

EPSS: 0.002090000 probability, percentile 0.111720000 (date 2026-09-12)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 a937dd1aa2d92291fe0a1860d17e90d8f206cd22 git Not specified
CNA Linux Linux affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 ad02d095439f89cbd6629420c7e3ba476457b83b git Not specified
CNA Linux Linux affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 1195483965a5f63d2dde18054ec7e50a23b9071c git Not specified
CNA Linux Linux affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 26709c8ffe73772eb69e68d553ac71d91228dccc git Not specified
CNA Linux Linux affected 2.6.12 Not specified
CNA Linux Linux unaffected 2.6.12 semver Not specified
CNA Linux Linux unaffected 6.12.109 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.50 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.4 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/1195483965a5f63d2dde18054ec7e50a23b9071c 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/a937dd1aa2d92291fe0a1860d17e90d8f206cd22 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/26709c8ffe73772eb69e68d553ac71d91228dccc 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/ad02d095439f89cbd6629420c7e3ba476457b83b 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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