CVE-2026-74542: netfs: Fix folio_queue ENOMEM in writeback by adding a mempool

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

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

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

netfs: Fix folio_queue ENOMEM in writeback by adding a mempool

Fix the handling of folio_queue allocation failure in writeback by adding a
mempool and passing in gfp_t flags to the rolling buffer functions that
allocate memory, using the mempool if gfp != GFP_KERNEL.

This is then extended upwards and the gfp to be used for a request is stored
in the netfs_io_request struct and is then used for both requests and
subrequests, eliminating the sleeping loops there.

The failure caused:

    folio != NULL
    WARNING: fs/netfs/write_issue.c:603 at netfs_writepages+0x883/0xa10 fs/netfs/write_issue.c:603, CPU#3: syz.0.17/5919

The Linux kernel CVE team has assigned CVE-2026-74542 to this issue.


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

	Issue introduced in 6.12 with commit cd0277ed0c188dd40e7744e89299af7b78831ca4 and fixed in 7.1.8 with commit 3f6d7f8a5416d852648d15a05e895f1195ee8a85
	Issue introduced in 6.12 with commit cd0277ed0c188dd40e7744e89299af7b78831ca4 and fixed in 7.2-rc6 with commit 1d78d56c43ef3768183e8370e7367b162700e049

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-2026-74542
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/buffered_read.c
	fs/netfs/internal.h
	fs/netfs/main.c
	fs/netfs/objects.c
	fs/netfs/read_pgpriv2.c
	fs/netfs/rolling_buffer.c
	fs/netfs/write_issue.c
	include/linux/netfs.h
	include/linux/rolling_buffer.h


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/3f6d7f8a5416d852648d15a05e895f1195ee8a85
	https://git.kernel.org/stable/c/1d78d56c43ef3768183e8370e7367b162700e049