linux-cve-announce - CVE-2022-49052: mm: fix unexpected zeroed page mapping with zram swap

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Message-ID: <2025022651-CVE-2022-49052-4ea2@gregkh>
Date: Wed, 26 Feb 2025 02:54:17 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2022-49052: mm: fix unexpected zeroed page mapping with zram swap

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

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

mm: fix unexpected zeroed page mapping with zram swap

Two processes under CLONE_VM cloning, user process can be corrupted by
seeing zeroed page unexpectedly.

      CPU A                        CPU B

  do_swap_page                do_swap_page
  SWP_SYNCHRONOUS_IO path     SWP_SYNCHRONOUS_IO path
  swap_readpage valid data
    swap_slot_free_notify
      delete zram entry
                              swap_readpage zeroed(invalid) data
                              pte_lock
                              map the *zero data* to userspace
                              pte_unlock
  pte_lock
  if (!pte_same)
    goto out_nomap;
  pte_unlock
  return and next refault will
  read zeroed data

The swap_slot_free_notify is bogus for CLONE_VM case since it doesn't
increase the refcount of swap slot at copy_mm so it couldn't catch up
whether it's safe or not to discard data from backing device.  In the
case, only the lock it could rely on to synchronize swap slot freeing is
page table lock.  Thus, this patch gets rid of the swap_slot_free_notify
function.  With this patch, CPU A will see correct data.

      CPU A                        CPU B

  do_swap_page                do_swap_page
  SWP_SYNCHRONOUS_IO path     SWP_SYNCHRONOUS_IO path
                              swap_readpage original data
                              pte_lock
                              map the original data
                              swap_free
                                swap_range_free
                                  bd_disk->fops->swap_slot_free_notify
  swap_readpage read zeroed data
                              pte_unlock
  pte_lock
  if (!pte_same)
    goto out_nomap;
  pte_unlock
  return
  on next refault will see mapped data by CPU B

The concern of the patch would increase memory consumption since it
could keep wasted memory with compressed form in zram as well as
uncompressed form in address space.  However, most of cases of zram uses
no readahead and do_swap_page is followed by swap_free so it will free
the compressed form from in zram quickly.

The Linux kernel CVE team has assigned CVE-2022-49052 to this issue.


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

	Issue introduced in 4.15 with commit 0bcac06f27d7528591c27ac2b093ccd71c5d0168 and fixed in 4.19.242 with commit f86d55cf616199404c05f5b0c5c41b17351baa02
	Issue introduced in 4.15 with commit 0bcac06f27d7528591c27ac2b093ccd71c5d0168 and fixed in 5.4.193 with commit f098f8b9820fe3f2e41aefc4329dfe8a3859d1c1
	Issue introduced in 4.15 with commit 0bcac06f27d7528591c27ac2b093ccd71c5d0168 and fixed in 5.10.112 with commit 20ed94f8181a25212e7404e44958e234f407624b
	Issue introduced in 4.15 with commit 0bcac06f27d7528591c27ac2b093ccd71c5d0168 and fixed in 5.15.35 with commit 12ba1d38115a101c45d8e0ca3aa1181fd148e57f
	Issue introduced in 4.15 with commit 0bcac06f27d7528591c27ac2b093ccd71c5d0168 and fixed in 5.17.4 with commit afac4b88699a06c8b9369f9d759a1ec3c254b788
	Issue introduced in 4.15 with commit 0bcac06f27d7528591c27ac2b093ccd71c5d0168 and fixed in 5.18 with commit e914d8f00391520ecc4495dd0ca0124538ab7119

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-2022-49052
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:
	mm/page_io.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/f86d55cf616199404c05f5b0c5c41b17351baa02
	https://git.kernel.org/stable/c/f098f8b9820fe3f2e41aefc4329dfe8a3859d1c1
	https://git.kernel.org/stable/c/20ed94f8181a25212e7404e44958e234f407624b
	https://git.kernel.org/stable/c/12ba1d38115a101c45d8e0ca3aa1181fd148e57f
	https://git.kernel.org/stable/c/afac4b88699a06c8b9369f9d759a1ec3c254b788
	https://git.kernel.org/stable/c/e914d8f00391520ecc4495dd0ca0124538ab7119