CVE-2026-46256: NFS/localio: prevent direct reclaim recursion into NFS via nfs_writepages

CVE-2026-46256: NFS/localio: prevent direct reclaim recursion into NFS via nfs_writepages

[Greg Kroah-Hartman]

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

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

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

NFS/localio: prevent direct reclaim recursion into NFS via nfs_writepages

LOCALIO is an NFS loopback mount optimization that avoids using the
network for READ, WRITE and COMMIT if the NFS client and server are
determined to be on the same system. But because LOCALIO is still
fundamentally "just NFS loopback mount" it is susceptible to recursion
deadlock via direct reclaim, e.g.: NFS LOCALIO down to XFS and then
back into NFS via nfs_writepages.

Fix LOCALIO's potential for direct reclaim deadlock by ensuring that
all its page cache allocations are done from GFP_NOFS context.

Thanks to Ben Coddington for pointing out commit ad22c7a043c2 ("xfs:
prevent stack overflows from page cache allocation").

The Linux kernel CVE team has assigned CVE-2026-46256 to this issue.


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

	Issue introduced in 6.12 with commit 70ba381e1a431245c137ed597ec6a05991c79bd9 and fixed in 6.18.14 with commit ae26a4cf2baf0a44c538dc093504d1994b02dade
	Issue introduced in 6.12 with commit 70ba381e1a431245c137ed597ec6a05991c79bd9 and fixed in 6.19.4 with commit 6a5de0c4fc0f217eea945d3d72c34ee30d72cbc9
	Issue introduced in 6.12 with commit 70ba381e1a431245c137ed597ec6a05991c79bd9 and fixed in 7.0 with commit 67435d2d8a33a75f9647724952cb1b18279d2e95

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-2026-46256
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/nfs/localio.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/ae26a4cf2baf0a44c538dc093504d1994b02dade
	https://git.kernel.org/stable/c/6a5de0c4fc0f217eea945d3d72c34ee30d72cbc9
	https://git.kernel.org/stable/c/67435d2d8a33a75f9647724952cb1b18279d2e95