CVE-2026-64396 (GCVE-0-2026-64396)
Vulnerability from cvelistv5
Published
2026-07-25 08:50
Modified
2026-08-17 04:54
Severity ?
8.8 (High) - CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix UAF of struct file_lock in SMB2_LOCK deferred-lock cancellation When a blocking byte-range lock request is deferred in the FILE_LOCK_DEFERRED path, ksmbd registers the asynchronous work into the connection's async_requests list via setup_async_work(). The cancel callback smb2_remove_blocked_lock() holds a reference to the flock. If the lock waiter is subsequently woken up but the work state is no longer KSMBD_WORK_ACTIVE (e.g., due to a concurrent cancellation), the cleanup path calls locks_free_lock(flock) without dequeuing the work from the async_requests list. Concurrently, smb2_cancel() walks the list under conn->request_lock and invokes the cancel callback, which then dereferences the already freed 'flock'. This leads to a slab-use-after-free inside __wake_up_common. Fix this by restructuring the cleanup logic after the worker returns from ksmbd_vfs_posix_lock_wait(). Move list_del(&smb_lock->llist) and release_async_work(work) to the top of the cleanup block. This guarantees that the async work is completely dequeued and serialized under conn->request_lock before locks_free_lock(flock) is called, rendering the flock unreachable for any concurrent smb2_cancel().
References
Impacted products
Vendor Product Version
Linux Linux Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
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{
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          "programFiles": [
            "fs/smb/server/smb2pdu.c"
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      ],
      "cpeApplicability": [
        {
          "nodes": [
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              "operator": "OR"
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: fix UAF of struct file_lock in SMB2_LOCK deferred-lock cancellation\n\nWhen a blocking byte-range lock request is deferred in the\nFILE_LOCK_DEFERRED path, ksmbd registers the asynchronous work into\nthe connection\u0027s async_requests list via setup_async_work(). The cancel\ncallback smb2_remove_blocked_lock() holds a reference to the flock.\n\nIf the lock waiter is subsequently woken up but the work state is no\nlonger KSMBD_WORK_ACTIVE (e.g., due to a concurrent cancellation), the\ncleanup path calls locks_free_lock(flock) without dequeuing the work from\nthe async_requests list. Concurrently, smb2_cancel() walks the list\nunder conn-\u003erequest_lock and invokes the cancel callback, which then\ndereferences the already freed \u0027flock\u0027. This leads to a slab-use-after-free\ninside __wake_up_common.\n\nFix this by restructuring the cleanup logic after the worker returns\nfrom ksmbd_vfs_posix_lock_wait(). Move list_del(\u0026smb_lock-\u003ellist) and\nrelease_async_work(work) to the top of the cleanup block. This guarantees\nthat the async work is completely dequeued and serialized under\nconn-\u003erequest_lock before locks_free_lock(flock) is called, rendering\nthe flock unreachable for any concurrent smb2_cancel()."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - ksmbd accepts remote SMB traffic over TCP port 445, and SMB2 LOCK, CLOSE, and CANCEL requests reach the vulnerable code through the network handler.\nAC:L - The attacker can create both conflicting file handles, obtain the deferred request\u0027s AsyncId, and control the CLOSE/CANCEL sequencing, so both sides of the race are attacker-controlled.\nPR:L - SMB2 LOCK requires a valid SMB session, tree connection, and session-owned open file handle. Any ordinary authenticated share user suffices; administrative privileges are unnecessary.\nUI:N - The attacker can create the handles, conflicting locks, and cancellation requests without any victim action.\nS:U - The UAF occurs within the host kernel\u0027s ksmbd security authority and does not inherently cross a separate virtualization or sandbox boundary.\nC:H - The file_lock UAF permits attacker-influenced slab reuse and stale kernel-pointer dereferences, making kernel memory disclosure defensible.\nI:H - The stale callback performs list deletion and wait-queue operations through freed or reallocated fields, enabling kernel heap corruption, arbitrary-write primitives, and potential code execution.\nA:H - The UAF reaches __locks_delete_block or __wake_up_common and can cause a kernel oops or panic; a remote attacker can repeatedly retrigger it."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T04:54:50.101Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/367c42a611fe488b7b03f1f6737f4dee0e8b20a2"
        },
        {
          "url": "https://git.kernel.org/stable/c/7703fd9aba1f2483c8e55f9ff73b7663e0761ed9"
        },
        {
          "url": "https://git.kernel.org/stable/c/463bbd79698513af4dad50fe1c573825f297ca2e"
        },
        {
          "url": "https://git.kernel.org/stable/c/5aa1cb01155f96824003baf7997cdf1f150caba3"
        },
        {
          "url": "https://git.kernel.org/stable/c/5c75275c0fc9a2deb0d8f5604edcb16f288171c8"
        },
        {
          "url": "https://git.kernel.org/stable/c/d20d1c8ba5765d1d12eefc0aee6385ab3f240e1e"
        }
      ],
      "title": "ksmbd: fix UAF of struct file_lock in SMB2_LOCK deferred-lock cancellation",
      "x_generator": {
        "engine": "bippy-1.2.0"
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  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-64396",
    "datePublished": "2026-07-25T08:50:40.993Z",
    "dateReserved": "2026-07-19T15:36:31.785Z",
    "dateUpdated": "2026-08-17T04:54:50.101Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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