FKIE_CVE-2026-98226

Vulnerability from fkie_nvd - Published: 2026-10-06 09:18 - Updated: 2026-10-06 09:18
Severity
Summary
In the Linux kernel, the following vulnerability has been resolved: mm, swap: fix SWAP_USAGE_OFFLIST_BIT collision with real usage count SWAP_USAGE_OFFLIST_BIT is embedded in the si->inuse_pages usage counter, and is meant to sit above any value that counter can reach. However, it is defined from BITS_PER_TYPE(atomic_t), so it is bit 30. On a system with 4 KiB pages the flag collides with the usage count once that count reaches 4 TiB. swap_usage_in_pages() masks bit 30 out, so whenever the real count has that bit set, every caller of it reads 4 TiB low: * /proc/swaps understates Used by 4 TiB. * A raw count of exactly 2^30 masks to zero, so try_to_unuse() takes its "if (!swap_usage_in_pages(si)) goto success;" early exit and swapoff tears the device down while pages are still swapped out. Nothing in the rest of swapoff aborts the teardown, so those pages are lost. Independently of swapoff, the collision also corrupts the counter and the plist. On a device in normal use, a free that leaves bit 30 set in the count makes swap_usage_sub() see the flag where there is only count, and call add_to_avail_list(). It clears the bit with fetch_and(~SWAP_USAGE_OFFLIST_BIT), leaving the stored count 4 TiB below the real one, and calls plist_add() on a device that is already listed, tripping the WARN_ON(!plist_node_empty(node)) in plist_add() and linking the node a second time. Change the definition of SWAP_USAGE_OFFLIST_BIT to be based on atomic_long_t instead. Note that the usage counter field itself is of this same type, so it is still a valid bit.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/0a41a46859df0d2bd7ed127197aac7c7389c00ed
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/12e9ac7bc5b254048f886bf421e3a15491106c1f
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/7c0d0d6de46076b43a2acaf1026b6648f8434c39
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "mm/swapfile.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "0a41a46859df0d2bd7ed127197aac7c7389c00ed",
              "status": "affected",
              "version": "b228386cf237e659cdf5d8037a19db0b0a06f6b5",
              "versionType": "git"
            },
            {
              "lessThan": "7c0d0d6de46076b43a2acaf1026b6648f8434c39",
              "status": "affected",
              "version": "b228386cf237e659cdf5d8037a19db0b0a06f6b5",
              "versionType": "git"
            },
            {
              "lessThan": "12e9ac7bc5b254048f886bf421e3a15491106c1f",
              "status": "affected",
              "version": "b228386cf237e659cdf5d8037a19db0b0a06f6b5",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "mm/swapfile.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.14"
            },
            {
              "lessThan": "6.14",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.54",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.8",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3-rc4",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm, swap: fix SWAP_USAGE_OFFLIST_BIT collision with real usage count\n\nSWAP_USAGE_OFFLIST_BIT is embedded in the si-\u003einuse_pages usage counter,\nand is meant to sit above any value that counter can reach.  However, it\nis defined from BITS_PER_TYPE(atomic_t), so it is bit 30.  On a system\nwith 4 KiB pages the flag collides with the usage count once that count\nreaches 4 TiB.\n\nswap_usage_in_pages() masks bit 30 out, so whenever the real count has\nthat bit set, every caller of it reads 4 TiB low:\n\n* /proc/swaps understates Used by 4 TiB.\n\n* A raw count of exactly 2^30 masks to zero, so try_to_unuse() takes its\n  \"if (!swap_usage_in_pages(si)) goto success;\" early exit and swapoff\n  tears the device down while pages are still swapped out. Nothing in\n  the rest of swapoff aborts the teardown, so those pages are lost.\n\nIndependently of swapoff, the collision also corrupts the counter and the\nplist.  On a device in normal use, a free that leaves bit 30 set in the\ncount makes swap_usage_sub() see the flag where there is only count, and\ncall add_to_avail_list().  It clears the bit with\nfetch_and(~SWAP_USAGE_OFFLIST_BIT), leaving the stored count 4 TiB below\nthe real one, and calls plist_add() on a device that is already listed,\ntripping the WARN_ON(!plist_node_empty(node)) in plist_add() and linking\nthe node a second time.\n\nChange the definition of SWAP_USAGE_OFFLIST_BIT to be based on\natomic_long_t instead.  Note that the usage counter field itself is of\nthis same type, so it is still a valid bit."
    }
  ],
  "id": "CVE-2026-98226",
  "lastModified": "2026-10-06T09:18:09.820",
  "metrics": {},
  "published": "2026-10-06T09:18:09.820",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/0a41a46859df0d2bd7ed127197aac7c7389c00ed"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/12e9ac7bc5b254048f886bf421e3a15491106c1f"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/7c0d0d6de46076b43a2acaf1026b6648f8434c39"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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