CVE-2026-64267: fuse: avoid 32-bit prune notification count wrap

CVE-2026-64267: fuse: avoid 32-bit prune notification count wrap

[Greg Kroah-Hartman]

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

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

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

fuse: avoid 32-bit prune notification count wrap

FUSE_NOTIFY_PRUNE validates the nodeid payload length with:

    size - sizeof(outarg) != outarg.count * sizeof(u64)

On 32-bit kernels, size_t is also 32 bits, so the daemon-controlled
count multiplication can wrap.  A prune notification with count
0x20000000 and no nodeid payload passes the check, enters the copy
loop, and asks the device copy path to read nodeids that are not
present in the userspace write buffer.  In QEMU this reaches the
fuse_copy_fill() BUG_ON(!err) path.

Validate the payload length with array_size() instead.  That accepts
exactly the same valid messages, but avoids wrapping arithmetic before
the copy loop consumes the count.

The Linux kernel CVE team has assigned CVE-2026-64267 to this issue.


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

	Issue introduced in 6.18 with commit 3f29d59e92a96d843c2ff10ebfed92ac26878658 and fixed in 6.18.39 with commit 6e2d84fdeac05bfd858e84a76353fdb84f23a43e
	Issue introduced in 6.18 with commit 3f29d59e92a96d843c2ff10ebfed92ac26878658 and fixed in 7.1.4 with commit c78c4b242299bc581e4987e5c2786c6f4760c516
	Issue introduced in 6.18 with commit 3f29d59e92a96d843c2ff10ebfed92ac26878658 and fixed in 7.2-rc1 with commit 54243797cedf55447b4c5d560e8cd709900061ae

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-2026-64267
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/fuse/dev.c
	fs/fuse/notify.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/6e2d84fdeac05bfd858e84a76353fdb84f23a43e
	https://git.kernel.org/stable/c/c78c4b242299bc581e4987e5c2786c6f4760c516
	https://git.kernel.org/stable/c/54243797cedf55447b4c5d560e8cd709900061ae