CVE-2026-89665

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 ]