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

Overview

In 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 ]

Affected

• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < cdc3299f7072777b09c9582a3b8b65bb163ddcf3
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 09a79d9ab35a39603c834e8f6333603292f9c816
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 5296a2442d12d45d6eea7b4d3ec3ffecc1821cac
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 1db456ffc22e045f49f7b9e62415a26b3f33f200
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < a937dd1aa2d92291fe0a1860d17e90d8f206cd22
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < ad02d095439f89cbd6629420c7e3ba476457b83b
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 1195483965a5f63d2dde18054ec7e50a23b9071c
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 26709c8ffe73772eb69e68d553ac71d91228dccc
• Linux 2.6.12

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

Vendor advisories

• Red Hat VEX · Moderate · affected: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat OpenShift Container Platform 4 · updated 2026-09-15 · vex