// For flags

CVE-2024-40950

mm: huge_memory: fix misused mapping_large_folio_support() for anon folios

Severity Score

"-"
*CVSS v-

Exploit Likelihood

*EPSS

Affected Versions

*CPE

Public Exploits

0
*Multiple Sources

Exploited in Wild

-
*KEV

Decision

Track
*SSVC
Descriptions

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

mm: huge_memory: fix misused mapping_large_folio_support() for anon folios

When I did a large folios split test, a WARNING "[ 5059.122759][ T166]
Cannot split file folio to non-0 order" was triggered. But the test cases
are only for anonmous folios. while mapping_large_folio_support() is only
reasonable for page cache folios.

In split_huge_page_to_list_to_order(), the folio passed to
mapping_large_folio_support() maybe anonmous folio. The folio_test_anon()
check is missing. So the split of the anonmous THP is failed. This is
also the same for shmem_mapping(). We'd better add a check for both. But
the shmem_mapping() in __split_huge_page() is not involved, as for
anonmous folios, the end parameter is set to -1, so (head[i].index >= end)
is always false. shmem_mapping() is not called.

Also add a VM_WARN_ON_ONCE() in mapping_large_folio_support() for anon
mapping, So we can detect the wrong use more easily.

THP folios maybe exist in the pagecache even the file system doesn't
support large folio, it is because when CONFIG_TRANSPARENT_HUGEPAGE is
enabled, khugepaged will try to collapse read-only file-backed pages to
THP. But the mapping does not actually support multi order large folios
properly.

Using /sys/kernel/debug/split_huge_pages to verify this, with this patch,
large anon THP is successfully split and the warning is ceased.

*Credits: N/A
CVSS Scores
Attack Vector
-
Attack Complexity
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Privileges Required
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User Interaction
-
Scope
-
Confidentiality
-
Integrity
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Availability
-
* Common Vulnerability Scoring System
SSVC
  • Decision:Track
Exploitation
None
Automatable
No
Tech. Impact
Partial
* Organization's Worst-case Scenario
Timeline
  • 2024-07-12 CVE Reserved
  • 2024-07-12 CVE Published
  • 2024-07-13 EPSS Updated
  • 2024-12-19 CVE Updated
  • ---------- Exploited in Wild
  • ---------- KEV Due Date
  • ---------- First Exploit
CWE
CAPEC
Affected Vendors, Products, and Versions
Vendor Product Version Other Status
Vendor Product Version Other Status <-- --> Vendor Product Version Other Status
Linux
Search vendor "Linux"
Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
>= 6.9 < 6.9.7
Search vendor "Linux" for product "Linux Kernel" and version " >= 6.9 < 6.9.7"
en
Affected
Linux
Search vendor "Linux"
Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
>= 6.9 < 6.10
Search vendor "Linux" for product "Linux Kernel" and version " >= 6.9 < 6.10"
en
Affected