CVE-2026-64298

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

NFSv4: include MAY_WRITE in open permission mask for O_TRUNC

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

nfs_open_permission_mask() builds the access mask passed to nfs_may_open(), which is the local authorization gate for OPENs the client serves itself from a cached write delegation via the can_open_delegated() path in nfs4_try_open_cached(). The mask is derived from O_ACCMODE alone, so an open(O_RDONLY | O_TRUNC) against a file the caller cannot write requests only MAY_READ 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 MAY_WRITE in the mask whenever O_TRUNC is set so the local check matches the access the server would have enforced.

Affected Software

References

• https://git.kernel.org/stable/c/22c1fd1355ad4ca27aa7f0fa02719122dd92d9de
• https://git.kernel.org/stable/c/30fdf4df6c3c00efec947e4ddf97f0fdd4473628
• https://git.kernel.org/stable/c/4817c8974315b666e895b7d1bb83cd3664c323b1
• https://git.kernel.org/stable/c/5140f099ecd8a2f2808b7f7b720ee1bad8468974
• https://git.kernel.org/stable/c/6bd7d0a06b53c4e797e1a9cea0d2d41aa1b26230
• https://git.kernel.org/stable/c/a937e92c1d00534b5c2e3e9f4381b7e988180797
• https://git.kernel.org/stable/c/cb148a2762d644bff1894728e8835a9a4b84f9ea
• https://git.kernel.org/stable/c/e36501b7d4abdcd6d69a7cb901b2f286b7a3d041