CVE-2026-64156: netfs, afs: Fix write skipping in dir/link writepages

From: Greg Kroah-Hartman <[email protected]>

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

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

netfs, afs: Fix write skipping in dir/link writepages

Fix netfs_write_single() and afs_single_writepages() to better handle a
write that would be skipped due to lock contention and WB_SYNC_NONE by
returning 1 from netfs_write_single() if it skipped and making
afs_single_writepages() skip also.  If a skip occurs, the inode must be
re-marked as the VFS may have cleared the mark.

This is really only theoretical for directories in netfs_write_single() as
the only path to that is through afs_single_writepages() that takes the
->validate_lock around it, thereby serialising it.

The Linux kernel CVE team has assigned CVE-2026-64156 to this issue.


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

	Issue introduced in 6.14 with commit 6dd80936618c4ff852d4db73aca400351d9bd9f0 and fixed in 6.18.34 with commit 77bb293049d61e04c12b24ebbffafaf5ab36af90
	Issue introduced in 6.14 with commit 6dd80936618c4ff852d4db73aca400351d9bd9f0 and fixed in 7.0.11 with commit f91e10435c0dd37c48b1b25e6236284f656ddc0c
	Issue introduced in 6.14 with commit 6dd80936618c4ff852d4db73aca400351d9bd9f0 and fixed in 7.1 with commit 9871938f99cc6cb266a77265491660e2375271f5

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-2026-64156
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/afs/dir.c
	fs/netfs/write_issue.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/77bb293049d61e04c12b24ebbffafaf5ab36af90
	https://git.kernel.org/stable/c/f91e10435c0dd37c48b1b25e6236284f656ddc0c
	https://git.kernel.org/stable/c/9871938f99cc6cb266a77265491660e2375271f5