ghsa-6p6f-gc59-4w3f
Vulnerability from github
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).
{
"affected": [],
"aliases": [
"CVE-2024-42234"
],
"database_specific": {
"cwe_ids": [
"CWE-415"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-08-07T16:15:46Z",
"severity": "MODERATE"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm: fix crashes from deferred split racing folio migration\n\nEven on 6.10-rc6, I\u0027ve been seeing elusive \"Bad page state\"s (often on\nflags when freeing, yet the flags shown are not bad: PG_locked had been\nset and cleared??), and VM_BUG_ON_PAGE(page_ref_count(page) == 0)s from\ndeferred_split_scan()\u0027s folio_put(), and a variety of other BUG and WARN\nsymptoms implying double free by deferred split and large folio migration.\n\n6.7 commit 9bcef5973e31 (\"mm: memcg: fix split queue list crash when large\nfolio migration\") was right to fix the memcg-dependent locking broken in\n85ce2c517ade (\"memcontrol: only transfer the memcg data for migration\"),\nbut missed a subtlety of deferred_split_scan(): it moves folios to its own\nlocal list to work on them without split_queue_lock, during which time\nfolio-\u003e_deferred_list is not empty, but even the \"right\" lock does nothing\nto secure the folio and the list it is on.\n\nFortunately, deferred_split_scan() is careful to use folio_try_get(): so\nfolio_migrate_mapping() can avoid the race by folio_undo_large_rmappable()\nwhile the old folio\u0027s reference count is temporarily frozen to 0 - adding\nsuch a freeze in the !mapping case too (originally, folio lock and\nunmapping and no swap cache left an anon folio unreachable, so no freezing\nwas needed there: but the deferred split queue offers a way to reach it).",
"id": "GHSA-6p6f-gc59-4w3f",
"modified": "2024-08-08T15:31:28Z",
"published": "2024-08-07T18:30:43Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-42234"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/be9581ea8c058d81154251cb0695987098996cad"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/fc7facce686b64201dbf0b9614cc1d0bfad70010"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.