CVE-2026-89697: nfsd: add fh_want_write() for early-verified SETATTR in nfsd_proc_setattr()

CVE-2026-89697: nfsd: add fh_want_write() for early-verified SETATTR in nfsd_proc_setattr()

[Greg Kroah-Hartman]

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

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

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

nfsd: add fh_want_write() for early-verified SETATTR in nfsd_proc_setattr()

The BOTH_TIME_SET branch calls fh_verify() early so setattr_prepare()
can inspect the dentry. This causes nfsd_setattr() to skip
fh_want_write(), so notify_change() runs without a mount write
reference.

Add the missing fh_want_write() call after the early fh_verify().

The Linux kernel CVE team has assigned CVE-2026-89697 to this issue.


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

	Issue introduced in 4.2 with commit cc265089ce1b176dde963c74b53593446ee7f99a and fixed in 6.12.109 with commit 15ca3b64a69caa6194bed8f98a20ed90a11c11dd
	Issue introduced in 4.2 with commit cc265089ce1b176dde963c74b53593446ee7f99a and fixed in 6.18.50 with commit 533964d420d385e11b08dd4c56c66ef5dcccaf08
	Issue introduced in 4.2 with commit cc265089ce1b176dde963c74b53593446ee7f99a and fixed in 7.2.4 with commit c4a409b86a92815181a8e9395c6bf1696ad19175
	Issue introduced in 4.2 with commit cc265089ce1b176dde963c74b53593446ee7f99a and fixed in 7.3-rc1 with commit 4e475be769aa9f7a2c1ce55a2b8592cfccacddcc
	Issue introduced in 3.18.46 with commit 1cb57d81cf20fe24b9e2e1daf57bfbdc24b77cd8

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-2026-89697
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/nfsd/nfsproc.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/15ca3b64a69caa6194bed8f98a20ed90a11c11dd
	https://git.kernel.org/stable/c/533964d420d385e11b08dd4c56c66ef5dcccaf08
	https://git.kernel.org/stable/c/c4a409b86a92815181a8e9395c6bf1696ad19175
	https://git.kernel.org/stable/c/4e475be769aa9f7a2c1ce55a2b8592cfccacddcc