GSD-2021-46988

Vulnerability from gsd - Updated: 2024-02-28 06:03
Details
In the Linux kernel, the following vulnerability has been resolved: userfaultfd: release page in error path to avoid BUG_ON Consider the following sequence of events: 1. Userspace issues a UFFD ioctl, which ends up calling into shmem_mfill_atomic_pte(). We successfully account the blocks, we shmem_alloc_page(), but then the copy_from_user() fails. We return -ENOENT. We don't release the page we allocated. 2. Our caller detects this error code, tries the copy_from_user() after dropping the mmap_lock, and retries, calling back into shmem_mfill_atomic_pte(). 3. Meanwhile, let's say another process filled up the tmpfs being used. 4. So shmem_mfill_atomic_pte() fails to account blocks this time, and immediately returns - without releasing the page. This triggers a BUG_ON in our caller, which asserts that the page should always be consumed, unless -ENOENT is returned. To fix this, detect if we have such a "dangling" page when accounting fails, and if so, release it before returning.
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{
  "gsd": {
    "metadata": {
      "exploitCode": "unknown",
      "remediation": "unknown",
      "reportConfidence": "confirmed",
      "type": "vulnerability"
    },
    "osvSchema": {
      "aliases": [
        "CVE-2021-46988"
      ],
      "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nuserfaultfd: release page in error path to avoid BUG_ON\n\nConsider the following sequence of events:\n\n1. Userspace issues a UFFD ioctl, which ends up calling into\n   shmem_mfill_atomic_pte(). We successfully account the blocks, we\n   shmem_alloc_page(), but then the copy_from_user() fails. We return\n   -ENOENT. We don\u0027t release the page we allocated.\n2. Our caller detects this error code, tries the copy_from_user() after\n   dropping the mmap_lock, and retries, calling back into\n   shmem_mfill_atomic_pte().\n3. Meanwhile, let\u0027s say another process filled up the tmpfs being used.\n4. So shmem_mfill_atomic_pte() fails to account blocks this time, and\n   immediately returns - without releasing the page.\n\nThis triggers a BUG_ON in our caller, which asserts that the page\nshould always be consumed, unless -ENOENT is returned.\n\nTo fix this, detect if we have such a \"dangling\" page when accounting\nfails, and if so, release it before returning.",
      "id": "GSD-2021-46988",
      "modified": "2024-02-28T06:03:57.654866Z",
      "schema_version": "1.4.0"
    }
  },
  "namespaces": {
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      "CVE_data_meta": {
        "ASSIGNER": "cve@kernel.org",
        "ID": "CVE-2021-46988",
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                    "version": {
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                          "version_affected": "\u003c",
                          "version_name": "cb658a453b93",
                          "version_value": "319116227e52"
                        },
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                          "version_value": "not down converted",
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            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nuserfaultfd: release page in error path to avoid BUG_ON\n\nConsider the following sequence of events:\n\n1. Userspace issues a UFFD ioctl, which ends up calling into\n   shmem_mfill_atomic_pte(). We successfully account the blocks, we\n   shmem_alloc_page(), but then the copy_from_user() fails. We return\n   -ENOENT. We don\u0027t release the page we allocated.\n2. Our caller detects this error code, tries the copy_from_user() after\n   dropping the mmap_lock, and retries, calling back into\n   shmem_mfill_atomic_pte().\n3. Meanwhile, let\u0027s say another process filled up the tmpfs being used.\n4. So shmem_mfill_atomic_pte() fails to account blocks this time, and\n   immediately returns - without releasing the page.\n\nThis triggers a BUG_ON in our caller, which asserts that the page\nshould always be consumed, unless -ENOENT is returned.\n\nTo fix this, detect if we have such a \"dangling\" page when accounting\nfails, and if so, release it before returning."
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      }
    },
    "nvd.nist.gov": {
      "cve": {
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nuserfaultfd: release page in error path to avoid BUG_ON\n\nConsider the following sequence of events:\n\n1. Userspace issues a UFFD ioctl, which ends up calling into\n   shmem_mfill_atomic_pte(). We successfully account the blocks, we\n   shmem_alloc_page(), but then the copy_from_user() fails. We return\n   -ENOENT. We don\u0027t release the page we allocated.\n2. Our caller detects this error code, tries the copy_from_user() after\n   dropping the mmap_lock, and retries, calling back into\n   shmem_mfill_atomic_pte().\n3. Meanwhile, let\u0027s say another process filled up the tmpfs being used.\n4. So shmem_mfill_atomic_pte() fails to account blocks this time, and\n   immediately returns - without releasing the page.\n\nThis triggers a BUG_ON in our caller, which asserts that the page\nshould always be consumed, unless -ENOENT is returned.\n\nTo fix this, detect if we have such a \"dangling\" page when accounting\nfails, and if so, release it before returning."
          }
        ],
        "id": "CVE-2021-46988",
        "lastModified": "2024-02-28T14:06:45.783",
        "metrics": {},
        "published": "2024-02-28T09:15:37.640",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Awaiting Analysis"
      }
    }
  }
}



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