CVE-2026-97610: netfs: Fix uninitialized return value in netfs_unbuffered_write()

CVE-2026-97610: netfs: Fix uninitialized return value in netfs_unbuffered_write()

[Greg Kroah-Hartman]

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

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

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

netfs: Fix uninitialized return value in netfs_unbuffered_write()

If preparation of the first subrequest fails,
netfs_unbuffered_write() exits its loop before ret is initialized. The
empty-iterator check can do the same.

For synchronous writes, netfs_unbuffered_write_iter_locked() may then
return an unrelated error instead of wreq->error. This is reachable
through CIFS if cifs_prepare_write() fails to reopen the file or obtain
credits.

Initialize ret to 0 so the caller returns wreq->error if no data was
written, or the number of bytes already written otherwise.

Found with Clang's -Wconditional-uninitialized.

The Linux kernel CVE team has assigned CVE-2026-97610 to this issue.


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

	Issue introduced in 6.18.17 with commit 72d08d2839649d1c5efbe375751f4473fa4486af and fixed in 6.18.53 with commit 3d038eebdbd400c3bc4b66bd8aa0dff0c2bcce26
	Issue introduced in 7.0 with commit a0b4c7a49137ed21279f354eb59f49ddae8dffc2 and fixed in 7.2.7 with commit 2e38d500471d097cda87d7d374bbc1b13493075d
	Issue introduced in 7.0 with commit a0b4c7a49137ed21279f354eb59f49ddae8dffc2 and fixed in 7.3-rc3 with commit f18e8774f4d3137fa0a5fb8ffa83d59a719666d8
	Issue introduced in 6.19.7 with commit 0c29f6d63122a0168d67cb8ecde5b4cf7fe4acb0

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-2026-97610
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/netfs/direct_write.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/3d038eebdbd400c3bc4b66bd8aa0dff0c2bcce26
	https://git.kernel.org/stable/c/2e38d500471d097cda87d7d374bbc1b13493075d
	https://git.kernel.org/stable/c/f18e8774f4d3137fa0a5fb8ffa83d59a719666d8