CVE-2024-42234 mm: fix crashes from deferred split racing folio migration

2024-08-0715:14:24

Linux

www.cve.org

linux kernel

vulnerability resolved

deferred split racing folio migration.

EPSS

Percentile

9.5%

JSON

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

mm: fix crashes from deferred split racing folio migration

Even on 6.10-rc6, I’ve been seeing elusive "Bad page state"s (often on
flags when freeing, yet the flags shown are not bad: PG_locked had been
set and cleared??), and VM_BUG_ON_PAGE(page_ref_count(page) == 0)s from
deferred_split_scan()'s folio_put(), and a variety of other BUG and WARN
symptoms implying double free by deferred split and large folio migration.

6.7 commit 9bcef5973e31 (“mm: memcg: fix split queue list crash when large
folio migration”) was right to fix the memcg-dependent locking broken in
85ce2c517ade (“memcontrol: only transfer the memcg data for migration”),
but missed a subtlety of deferred_split_scan(): it moves folios to its own
local list to work on them without split_queue_lock, during which time
folio->_deferred_list is not empty, but even the “right” lock does nothing
to secure the folio and the list it is on.

Fortunately, deferred_split_scan() is careful to use folio_try_get(): so
folio_migrate_mapping() can avoid the race by folio_undo_large_rmappable()
while the old folio’s reference count is temporarily frozen to 0 - adding
such a freeze in the !mapping case too (originally, folio lock and
unmapping and no swap cache left an anon folio unreachable, so no freezing
was needed there: but the deferred split queue offers a way to reach it).

CNA Affected

[
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "unaffected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "mm/memcontrol.c",
      "mm/migrate.c"
    ],
    "versions": [
      {
        "version": "9bcef5973e31",
        "lessThan": "fc7facce686b",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "9bcef5973e31",
        "lessThan": "be9581ea8c05",
        "status": "affected",
        "versionType": "git"
      }
    ]
  },
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "affected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "mm/memcontrol.c",
      "mm/migrate.c"
    ],
    "versions": [
      {
        "version": "6.7",
        "status": "affected"
      },
      {
        "version": "0",
        "lessThan": "6.7",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.9.10",
        "lessThanOrEqual": "6.9.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.10",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]