CVE-2026-64298

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

NFSv4: include MAYWRITE in open permission mask for OTRUNC

POSIX requires write permission to truncate a file, so an open() that specifies OTRUNC must be authorized for write access regardless of the OACCMODE access mode.

nfsopenpermissionmask() builds the access mask passed to nfsmayopen(), which is the local authorization gate for OPENs the client serves itself from a cached write delegation via the canopendelegated() path in nfs4tryopencached(). The mask is derived from OACCMODE alone, so an open(ORDONLY | OTRUNC) against a file the caller cannot write requests only MAYREAD and passes the local check. The OPEN is then satisfied locally and the truncation is issued to the server as a SETATTR(size=0) over the delegation stateid, which the server accepts under standard write-delegation semantics. POSIX requires that this open fail with EACCES.

Include MAYWRITE in the mask whenever OTRUNC is set so the local check matches the access the server would have enforced.