CVE-2026-74486: binfmt_misc: use exe_file_deny_write_access() for the interpreter clone

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

binfmtmisc: use exefiledenywriteaccess() for the interpreter clone

For MISCFMTOPENFILE entries loadmiscbinary() clones the registered interpreter file and denies write access to the clone via plain denywriteaccess(). The clone is installed as bprm->interpreter and later released by the exec machinery through exefileallowwriteaccess() which skips the iwritecount increment for files with FMODEFSNOTIFYHSM set.

The deny and allow side can therefore come to different conclusions when pre-content watches are in play: if a pre-content watch is added to the interpreter after registration every subsequent exec through that entry takes a write denial on the clone that is never paired with a write allowance, driving the interpreter inode's iwritecount further down with each exec and leaving the interpreter unwritable even after the entry and all its users are gone.

Take the write denial via exefiledenywriteaccess() so both sides of the pairing base their decision on the same file mode, and propagate failure instead of silently ignoring it: an interpreter that is concurrently open for writing now fails the exec with ETXTBSY, exactly like an interpreter freshly opened via openexec() would.