CVE-2026-89674

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

nfsd: fix XDR length calculation in nfsd4ffencode_layoutget

The XDR buffer size calculation in nfsd4ffencode_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 xdrencodeopaque() actually

   writes "4 + xdralignsize(len)" bytes

• dslen omits the flags and statscollect_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 xdralignsize() for all variable-length opaque

fields, and correcting the header constants.