linux-cve-announce - CVE-2025-21861: mm/migrate_device: don't add folio to be freed to LRU in migrate_device

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Message-ID: <2025031216-CVE-2025-21861-c775@gregkh>
Date: Wed, 12 Mar 2025 10:42:27 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-21861: mm/migrate_device: don't add folio to be freed to LRU in migrate_device_finalize()

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

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

mm/migrate_device: don't add folio to be freed to LRU in migrate_device_finalize()

If migration succeeded, we called
folio_migrate_flags()->mem_cgroup_migrate() to migrate the memcg from the
old to the new folio.  This will set memcg_data of the old folio to 0.

Similarly, if migration failed, memcg_data of the dst folio is left unset.

If we call folio_putback_lru() on such folios (memcg_data == 0), we will
add the folio to be freed to the LRU, making memcg code unhappy.  Running
the hmm selftests:

  # ./hmm-tests
  ...
  #  RUN           hmm.hmm_device_private.migrate ...
  [  102.078007][T14893] page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x7ff27d200 pfn:0x13cc00
  [  102.079974][T14893] anon flags: 0x17ff00000020018(uptodate|dirty|swapbacked|node=0|zone=2|lastcpupid=0x7ff)
  [  102.082037][T14893] raw: 017ff00000020018 dead000000000100 dead000000000122 ffff8881353896c9
  [  102.083687][T14893] raw: 00000007ff27d200 0000000000000000 00000001ffffffff 0000000000000000
  [  102.085331][T14893] page dumped because: VM_WARN_ON_ONCE_FOLIO(!memcg && !mem_cgroup_disabled())
  [  102.087230][T14893] ------------[ cut here ]------------
  [  102.088279][T14893] WARNING: CPU: 0 PID: 14893 at ./include/linux/memcontrol.h:726 folio_lruvec_lock_irqsave+0x10e/0x170
  [  102.090478][T14893] Modules linked in:
  [  102.091244][T14893] CPU: 0 UID: 0 PID: 14893 Comm: hmm-tests Not tainted 6.13.0-09623-g6c216bc522fd #151
  [  102.093089][T14893] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-2.fc40 04/01/2014
  [  102.094848][T14893] RIP: 0010:folio_lruvec_lock_irqsave+0x10e/0x170
  [  102.096104][T14893] Code: ...
  [  102.099908][T14893] RSP: 0018:ffffc900236c37b0 EFLAGS: 00010293
  [  102.101152][T14893] RAX: 0000000000000000 RBX: ffffea0004f30000 RCX: ffffffff8183f426
  [  102.102684][T14893] RDX: ffff8881063cb880 RSI: ffffffff81b8117f RDI: ffff8881063cb880
  [  102.104227][T14893] RBP: 0000000000000000 R08: 0000000000000005 R09: 0000000000000000
  [  102.105757][T14893] R10: 0000000000000001 R11: 0000000000000002 R12: ffffc900236c37d8
  [  102.107296][T14893] R13: ffff888277a2bcb0 R14: 000000000000001f R15: 0000000000000000
  [  102.108830][T14893] FS:  00007ff27dbdd740(0000) GS:ffff888277a00000(0000) knlGS:0000000000000000
  [  102.110643][T14893] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  [  102.111924][T14893] CR2: 00007ff27d400000 CR3: 000000010866e000 CR4: 0000000000750ef0
  [  102.113478][T14893] PKRU: 55555554
  [  102.114172][T14893] Call Trace:
  [  102.114805][T14893]  <TASK>
  [  102.115397][T14893]  ? folio_lruvec_lock_irqsave+0x10e/0x170
  [  102.116547][T14893]  ? __warn.cold+0x110/0x210
  [  102.117461][T14893]  ? folio_lruvec_lock_irqsave+0x10e/0x170
  [  102.118667][T14893]  ? report_bug+0x1b9/0x320
  [  102.119571][T14893]  ? handle_bug+0x54/0x90
  [  102.120494][T14893]  ? exc_invalid_op+0x17/0x50
  [  102.121433][T14893]  ? asm_exc_invalid_op+0x1a/0x20
  [  102.122435][T14893]  ? __wake_up_klogd.part.0+0x76/0xd0
  [  102.123506][T14893]  ? dump_page+0x4f/0x60
  [  102.124352][T14893]  ? folio_lruvec_lock_irqsave+0x10e/0x170
  [  102.125500][T14893]  folio_batch_move_lru+0xd4/0x200
  [  102.126577][T14893]  ? __pfx_lru_add+0x10/0x10
  [  102.127505][T14893]  __folio_batch_add_and_move+0x391/0x720
  [  102.128633][T14893]  ? __pfx_lru_add+0x10/0x10
  [  102.129550][T14893]  folio_putback_lru+0x16/0x80
  [  102.130564][T14893]  migrate_device_finalize+0x9b/0x530
  [  102.131640][T14893]  dmirror_migrate_to_device.constprop.0+0x7c5/0xad0
  [  102.133047][T14893]  dmirror_fops_unlocked_ioctl+0x89b/0xc80

Likely, nothing else goes wrong: putting the last folio reference will
remove the folio from the LRU again.  So besides memcg complaining, adding
the folio to be freed to the LRU is just an unnecessary step.

The new flow resembles what we have in migrate_folio_move(): add the dst
to the lru, remove migration ptes, unlock and unref dst.

The Linux kernel CVE team has assigned CVE-2025-21861 to this issue.


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

	Issue introduced in 4.14 with commit 8763cb45ab967a92a5ee49e9c544c0f0ea90e2d6 and fixed in 6.12.17 with commit 3f9240d59e9a95d19f06120bfd1d0e681c6c0ac7
	Issue introduced in 4.14 with commit 8763cb45ab967a92a5ee49e9c544c0f0ea90e2d6 and fixed in 6.13.5 with commit 069dd21ea8262204f94737878389c2815a054a9e
	Issue introduced in 4.14 with commit 8763cb45ab967a92a5ee49e9c544c0f0ea90e2d6 and fixed in 6.14-rc4 with commit 41cddf83d8b00f29fd105e7a0777366edc69a5cf

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-2025-21861
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/migrate_device.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/3f9240d59e9a95d19f06120bfd1d0e681c6c0ac7
	https://git.kernel.org/stable/c/069dd21ea8262204f94737878389c2815a054a9e
	https://git.kernel.org/stable/c/41cddf83d8b00f29fd105e7a0777366edc69a5cf