Subject: CVE-2024-36943: fs/proc/task_mmu: fix loss of young/dirty bits during pagemap scan

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

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

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

fs/proc/task_mmu: fix loss of young/dirty bits during pagemap scan

make_uffd_wp_pte() was previously doing:

  pte = ptep_get(ptep);
  ptep_modify_prot_start(ptep);
  pte = pte_mkuffd_wp(pte);
  ptep_modify_prot_commit(ptep, pte);

But if another thread accessed or dirtied the pte between the first 2
calls, this could lead to loss of that information.  Since
ptep_modify_prot_start() gets and clears atomically, the following is the
correct pattern and prevents any possible race.  Any access after the
first call would see an invalid pte and cause a fault:

  pte = ptep_modify_prot_start(ptep);
  pte = pte_mkuffd_wp(pte);
  ptep_modify_prot_commit(ptep, pte);

The Linux kernel CVE team has assigned CVE-2024-36943 to this issue.

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

	Issue introduced in 6.7 with commit 52526ca7fdb9 and fixed in 6.8.10 with commit 74b3d66f91d9
	Issue introduced in 6.7 with commit 52526ca7fdb9 and fixed in 6.9 with commit c70dce4982ce

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-2024-36943
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/proc/task_mmu.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/74b3d66f91d9f539f99faad74d796fa9a389a015
	https://git.kernel.org/stable/c/c70dce4982ce1718bf978a35f8e26160b82081f4