CVE-2026-80775 (GCVE-0-2026-80775)

Vulnerability from cvelistv5 – Published: 2026-09-04 15:12 – Updated: 2026-10-19 08:43
VLAI
Title
futex: Fix race on the initial mm->futex.phash.ref allocation
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.
Severity
No CVSS data available.
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 7061 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: d9b05321e21e4b218de4ce8a590bf375f58b6346 , < 86d12b34bafc9a4c271a9edefea88855a934d6e5 (git)
Affected: d9b05321e21e4b218de4ce8a590bf375f58b6346 , < ff252ed45c8263525f2f54d81c5fa6d547fba344 (git)
Affected: d9b05321e21e4b218de4ce8a590bf375f58b6346 , < c4b4972d8edcdf50b6518f55119e129d2f668a10 (git)
Affected: d9b05321e21e4b218de4ce8a590bf375f58b6346 , < bde0238083647381d4747355c5a19115a3422b96 (git)
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Linux Linux Affected: 6.17
Unaffected: 0 , < 6.17 (semver)
Unaffected: 6.18.47 , ≤ 6.18.* (semver)
Unaffected: 7.1.11 , ≤ 7.1.* (semver)
Unaffected: 7.2.1 , ≤ 7.2.* (semver)
Unaffected: 7.3 , ≤ * (original_commit_for_fix)
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{
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          "product": "Linux",
          "programFiles": [
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          "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."
        }
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        "dateUpdated": "2026-10-19T08:43:31.761Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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        },
        {
          "url": "https://git.kernel.org/stable/c/bde0238083647381d4747355c5a19115a3422b96"
        }
      ],
      "title": "futex: Fix race on the initial mm-\u003efutex.phash.ref allocation",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-80775",
    "datePublished": "2026-09-04T15:12:47.391Z",
    "dateReserved": "2026-08-26T14:34:25.792Z",
    "dateUpdated": "2026-10-19T08:43:31.761Z",
    "state": "PUBLISHED"
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            "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": "2026-10-19T09:17:11.683",
        "metrics": {},
        "published": "2026-09-04T16:18:03.123",
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      "current_release_date": "2026-10-20T23:29:26+00:00",
      "cve": "CVE-2026-80775",
      "id": "CVE-2026-80775",
      "initial_release_date": "2026-09-04T00:00:00+00:00",
      "product_status:fixed": "307",
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      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: futex: Fix race on the initial mm-\u003efutex.phash.ref allocation",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-80775.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-10-22T23:52:48Z",
      "cve": "CVE-2026-80775",
      "id": "CVE-2026-80775",
      "initial_release_date": "2026-09-08T17:17:59Z",
      "product_status:known_affected": "0",
      "product_status:known_not_affected": "353",
      "product_status:recommended": "124",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-80775",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/2026/cve-2026-80775.json",
      "version": "4"
    }
  }
}



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