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FKIE_CVE-2026-80775

Vulnerability from fkie_nvd - Published: 2026-09-04 16:18 - Updated: 2026-09-04 16:18
Severity
Summary
In the Linux kernel, the following vulnerability has been resolved: futex: Fix race on the initial mm->futex.phash.ref allocation futex_hash_allocate() allocates mm->futex.phash.ref without any locking. Commit d9b05321e21e ("futex: Move futex_hash_free() back to __mmput()") moved the allocation here and assumed that the process has just a single thread at this point. Commit ee9dce44362b ("futex: Drop CLONE_THREAD requirement for private default hash alloc") widened need_futex_hash_allocate_default() to cover any CLONE_VM clone, but left out vfork because the parent is suspended and cannot race. That no longer holds once vfork is nested. If a vfork child calls vfork again and is then killed with SIGKILL, the parent is released from its vfork wait and runs concurrently with the grandchild in the same mm. Neither of them went through futex_hash_allocate_default(). When both call prctl(PR_FUTEX_HASH, PR_FUTEX_HASH_SET_SLOTS) at the same time, each one sees mm->futex.phash.ref as NULL and stores its own percpu counter. Only the last store survives. The counter stored first is no longer reachable from the mm, so the references on it are not seen by __futex_ref_atomic_end(). A private hash that still has references is then considered dead and freed, and a task that still holds one of its buckets writes into freed memory in futex_q_lock(). Store the counter once with cmpxchg() and let the loser free_percpu() its own. The initial reference has to be taken before the store, otherwise another task can install a private hash while the counter is still 0.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/86d12b34bafc9a4c271a9edefea88855a934d6e5
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/bde0238083647381d4747355c5a19115a3422b96
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/c4b4972d8edcdf50b6518f55119e129d2f668a10
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/ff252ed45c8263525f2f54d81c5fa6d547fba344
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "kernel/futex/core.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "86d12b34bafc9a4c271a9edefea88855a934d6e5",
              "status": "affected",
              "version": "d9b05321e21e4b218de4ce8a590bf375f58b6346",
              "versionType": "git"
            },
            {
              "lessThan": "ff252ed45c8263525f2f54d81c5fa6d547fba344",
              "status": "affected",
              "version": "d9b05321e21e4b218de4ce8a590bf375f58b6346",
              "versionType": "git"
            },
            {
              "lessThan": "c4b4972d8edcdf50b6518f55119e129d2f668a10",
              "status": "affected",
              "version": "d9b05321e21e4b218de4ce8a590bf375f58b6346",
              "versionType": "git"
            },
            {
              "lessThan": "bde0238083647381d4747355c5a19115a3422b96",
              "status": "affected",
              "version": "d9b05321e21e4b218de4ce8a590bf375f58b6346",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "kernel/futex/core.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.17"
            },
            {
              "lessThan": "6.17",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.47",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.11",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.1",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3-rc1",
              "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\nfutex: Fix race on the initial mm-\u003efutex.phash.ref allocation\n\nfutex_hash_allocate() allocates mm-\u003efutex.phash.ref without any locking.\nCommit d9b05321e21e (\"futex: Move futex_hash_free() back to __mmput()\")\nmoved the allocation here and assumed that the process has just a single\nthread at this point.\n\nCommit ee9dce44362b (\"futex: Drop CLONE_THREAD requirement for private\ndefault hash alloc\") widened need_futex_hash_allocate_default() to cover\nany CLONE_VM clone, but left out vfork because the parent is suspended and\ncannot race.\n\nThat no longer holds once vfork is nested. If a vfork child calls vfork\nagain and is then killed with SIGKILL, the parent is released from its\nvfork wait and runs concurrently with the grandchild in the same mm.\nNeither of them went through futex_hash_allocate_default().\n\nWhen both call prctl(PR_FUTEX_HASH, PR_FUTEX_HASH_SET_SLOTS) at the same\ntime, each one sees mm-\u003efutex.phash.ref as NULL and stores its own percpu\ncounter. Only the last store survives. The counter stored first is no\nlonger reachable from the mm, so the references on it are not seen by\n__futex_ref_atomic_end(). A private hash that still has references is then\nconsidered dead and freed, and a task that still holds one of its buckets\nwrites into freed memory in futex_q_lock().\n\nStore the counter once with cmpxchg() and let the loser free_percpu() its\nown. The initial reference has to be taken before the store, otherwise\nanother task can install a private hash while the counter is still 0."
    }
  ],
  "id": "CVE-2026-80775",
  "lastModified": "2026-09-04T16:18:03.123",
  "metrics": {},
  "published": "2026-09-04T16:18:03.123",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/86d12b34bafc9a4c271a9edefea88855a934d6e5"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/bde0238083647381d4747355c5a19115a3422b96"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/c4b4972d8edcdf50b6518f55119e129d2f668a10"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/ff252ed45c8263525f2f54d81c5fa6d547fba344"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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