CVE-2026-31589

Description

In the Linux kernel, the following vulnerability has been resolved: mm: call ->free_folio() directly in folio_unmap_invalidate() We can only call filemap_free_folio() if we have a reference to (or hold a lock on) the mapping. Otherwise, we've already removed the folio from the mapping so it no longer pins the mapping and the mapping can be removed, causing a use-after-free when accessing mapping->a_ops. Follow the same pattern as __remove_mapping() and load the free_folio function pointer before dropping the lock on the mapping. That lets us make filemap_free_folio() static as this was the only caller outside filemap.c.

CVSS Details

CVSS Score

9.8

Severity

CRITICAL

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Configurations (Affected Products)

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* - VULNERABLE

Linux Kernel (主分支及稳定分支，未包含修复补丁的版本)

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

/*
 * Conceptual PoC for CVE-2026-31589
 * This demonstrates the vulnerable logic where mapping->a_ops is accessed
 * after the potential release of the mapping structure.
 */

#include <linux/mm.h>
#include <linux/pagemap.h>

// Vulnerable Logic Simulation
void vulnerable_folio_unmap(struct folio *folio) {
    struct address_space *mapping = folio->mapping;

    // Simulate dropping the lock or reference
    // mapping might be freed here in a race condition
    
    // Unsafe access to mapping->a_ops after potential free
    if (mapping && mapping->a_ops->free_folio) {
        mapping->a_ops->free_folio(mapping, folio);
    }
}

// Fixed Logic Simulation
void fixed_folio_unmap(struct folio *folio) {
    struct address_space *mapping = folio->mapping;
    void (*free_folio)(struct address_space *, struct folio *);

    // Load the function pointer BEFORE dropping the lock/unpinning
    free_folio = mapping->a_ops->free_folio;

    // Lock dropped / mapping potentially unpinned here

    // Use the cached pointer safely
    if (free_folio) {
        free_folio(mapping, folio);
    }
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-31589
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-31589
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-31589/
[4] VulDB https://vuldb.com/cve/CVE-2026-31589
[5] https://git.kernel.org/stable/c/615d9bb2ccad42f9e21d837431e401db2e471195
[6] https://git.kernel.org/stable/c/b667df39d98a7a24be7c2a40ff0863dac1ad2cd7
[7] https://git.kernel.org/stable/c/c330e65ea59c4805d6ab6757c4ddfe8c63acef31
[8] https://git.kernel.org/stable/c/efc52947247a21bbf79059539bbbd40f4ea76f00

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-31589", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-24T15:16:34.700", "lastModified": "2026-05-07T06:16:03.710", "vulnStatus": "Modified", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm: call ->free_folio() directly in folio_unmap_invalidate()\n\nWe can only call filemap_free_folio() if we have a reference to (or hold a\nlock on) the mapping. Otherwise, we've already removed the folio from the\nmapping so it no longer pins the mapping and the mapping can be removed,\ncausing a use-after-free when accessing mapping->a_ops.\n\nFollow the same pattern as __remove_mapping() and load the free_folio\nfunction pointer before dropping the lock on the mapping. That lets us\nmake filemap_free_folio() static as this was the only caller outside\nfilemap.c."}], "metrics": {"cvssMetricV31": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "baseScore": 9.8, "baseSeverity": "CRITICAL", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 5.9}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-416"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.14", "versionEndExcluding": "6.19.14", "matchCriteriaId": "24221FC1-03CA-4C3B-99B7-27AFF9FC5FAE"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "7.0", "versionEndExcluding": "7.0.1", "matchCriteriaId": "9B5888AB-7403-4335-89E4-21CC0B48366A"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/615d9bb2ccad42f9e21d837431e401db2e471195", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/b667df39d98a7a24be7c2a40ff0863dac1ad2cd7", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/c330e65ea59c4805d6ab6757c4ddfe8c63acef31", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/efc52947247a21bbf79059539bbbd40f4ea76f00", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}]}}