CVE-2026-64062: netfs: Fix potential deadlock in write-through mode

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

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

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

netfs: Fix potential deadlock in write-through mode

Fix netfs_advance_writethrough() to always unlock the supplied folio and to
mark it dirty if it isn't yet written to the end.  Unfortunately, it can't
be marked for writeback until the folio is done with as that may cause a
deadlock against mmapped reads and writes.

Even though it has been marked dirty, premature writeback can't occur as
the caller is holding both inode->i_rwsem (which will prevent concurrent
truncation, fallocation, DIO and other writes) and ictx->wb_lock (which
will cause flushing to wait and writeback to skip or wait).

Note that this may be easier to deal with once the queuing of folios is
split from the generation of subrequests.

The Linux kernel CVE team has assigned CVE-2026-64062 to this issue.


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

	Issue introduced in 6.10 with commit 288ace2f57c9d06dd2e42bd80d03747d879a4068 and fixed in 6.12.92 with commit 1468f39243ccb155b6d97f9a9932f610d1205d75
	Issue introduced in 6.10 with commit 288ace2f57c9d06dd2e42bd80d03747d879a4068 and fixed in 6.18.34 with commit 003aa0dd26c964025acd6d1213bcdbd674db2ca9
	Issue introduced in 6.10 with commit 288ace2f57c9d06dd2e42bd80d03747d879a4068 and fixed in 7.0.11 with commit e40e9cbf3ee4d30ee9a97bd128c85500b6ad0da1
	Issue introduced in 6.10 with commit 288ace2f57c9d06dd2e42bd80d03747d879a4068 and fixed in 7.1 with commit b6a4ae1634b3ad2aaa05222e53d36da532852faf

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-2026-64062
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/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/1468f39243ccb155b6d97f9a9932f610d1205d75
	https://git.kernel.org/stable/c/003aa0dd26c964025acd6d1213bcdbd674db2ca9
	https://git.kernel.org/stable/c/e40e9cbf3ee4d30ee9a97bd128c85500b6ad0da1
	https://git.kernel.org/stable/c/b6a4ae1634b3ad2aaa05222e53d36da532852faf