CVE-2026-74487: binfmt_misc: restore write access when removing an entry

CVE-2026-74487: binfmt_misc: restore write access when removing an entry

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

binfmt_misc: restore write access when removing an entry

Registering an entry with the MISC_FMT_OPEN_FILE flag opens the
interpreter via open_exec() which denies write access to it for as
long as the entry exists. Removing the entry closes the interpreter
file via filp_close() but never restores write access, leaving the
inode's i_writecount permanently negative. Opening the interpreter
for writing keeps failing with ETXTBSY long after the entry is gone
until the inode is evicted from the inode cache.

Commit 90f601b497d7 ("binfmt_misc: restore write access before
closing files opened by open_exec()") fixed the same imbalance in the
error path of bm_register_write() but the actual removal path has
been leaking the write denial since the introduction of the flag.

Restore write access in put_binfmt_handler() before closing the
interpreter file.

The Linux kernel CVE team has assigned CVE-2026-74487 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 4.8 with commit 948b701a607f123df92ed29084413e5dd8cda2ed and fixed in 6.18.44 with commit fdc1d702bf3001586221fa07e598e876a0a854c5
	Issue introduced in 4.8 with commit 948b701a607f123df92ed29084413e5dd8cda2ed and fixed in 7.1.8 with commit 3b522487a3a9162b1b519eefde7998d103e3e07b
	Issue introduced in 4.8 with commit 948b701a607f123df92ed29084413e5dd8cda2ed and fixed in 7.2-rc6 with commit db1856ea9196cf6e015d12199a34c0b9313c7bfa

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-74487
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/binfmt_misc.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/fdc1d702bf3001586221fa07e598e876a0a854c5
	https://git.kernel.org/stable/c/3b522487a3a9162b1b519eefde7998d103e3e07b
	https://git.kernel.org/stable/c/db1856ea9196cf6e015d12199a34c0b9313c7bfa