CVE-2026-80724: ptp: vmclock: prevent read-only mappings from becoming writable

CVE-2026-80724: ptp: vmclock: prevent read-only mappings from becoming writable

[Greg Kroah-Hartman]

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

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

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

ptp: vmclock: prevent read-only mappings from becoming writable

vmclock_miscdev_mmap() rejects writable mappings of the shared vmclock
ABI page with -EROFS, but leaves VM_MAYWRITE set.  Userspace can map the
page read-only and then upgrade it to writable with mprotect(), after
which the guest can corrupt the host-written timekeeping data (sequence
counter, UTC time, TSC offset) that the vmclock ABI defines as read-only.

Clear VM_MAYWRITE on the read-only path so the mapping cannot be
upgraded, as i915 does for its read-only objects and as fixed in drm/vc4
(CVE-2026-68445) and drm/panthor (CVE-2024-53071).

The Linux kernel CVE team has assigned CVE-2026-80724 to this issue.


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

	Issue introduced in 6.13 with commit 20503272422693d793b84f88bf23fe4e955d3a33 and fixed in 6.18.47 with commit 5b4f2bec7bea6c04084d720d731bedee7caf878d
	Issue introduced in 6.13 with commit 20503272422693d793b84f88bf23fe4e955d3a33 and fixed in 7.1.11 with commit 2496e141827102d6af512950057d402a2cfb2bfc
	Issue introduced in 6.13 with commit 20503272422693d793b84f88bf23fe4e955d3a33 and fixed in 7.2.1 with commit 2e596e7814ba38cdc129991058b6c254ed37cb11

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-2026-80724
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:
	drivers/ptp/ptp_vmclock.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/5b4f2bec7bea6c04084d720d731bedee7caf878d
	https://git.kernel.org/stable/c/2496e141827102d6af512950057d402a2cfb2bfc
	https://git.kernel.org/stable/c/2e596e7814ba38cdc129991058b6c254ed37cb11
	https://git.kernel.org/stable/c/a5edadbae57e2298a56cf7a4e774a027905a331f