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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't 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's 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."}, {"lang": "es", "value": "En el kernel de Linux, se resolvi\u00f3 la siguiente vulnerabilidad: userfaultfd: publicar p\u00e1gina en ruta de error para evitar BUG_ON Considere la siguiente secuencia de eventos: 1. Userspace emite un ioctl UFFD, que termina llamando a shmem_mfill_atomic_pte(). Contamos con \u00e9xito los bloques, usamos shmem_alloc_page(), pero luego copy_from_user() falla. Volvemos -ENOENT. No publicamos la p\u00e1gina que asignamos. 2. Nuestra persona que llama detecta este c\u00f3digo de error, intenta copiar_from_user() despu\u00e9s de descartar mmap_lock y vuelve a intentarlo, volviendo a llamar a shmem_mfill_atomic_pte(). 3. Mientras tanto, digamos que otro proceso llen\u00f3 los tmpfs que se estaban utilizando. 4. Entonces shmem_mfill_atomic_pte() no logra bloquear la cuenta esta vez y regresa inmediatamente, sin liberar la p\u00e1gina. Esto desencadena un BUG_ON en nuestra persona que llama, que afirma que la p\u00e1gina siempre debe consumirse, a menos que se devuelva -ENOENT. Para solucionar este problema, detectar si tenemos esa p\u00e1gina \"colgante\" cuando falla la contabilidad y, en caso afirmativo, liberarla antes de regresar."}], "id": "CVE-2021-46988", "lastModified": "2024-12-24T14:25:32.130", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "LOCAL", "availabilityImpact": "HIGH", "baseScore": 5.5, "baseSeverity": "MEDIUM", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "version": "3.1"}, "exploitabilityScore": 1.8, "impactScore": 3.6, "source": "[email protected]", "type": "Primary"}]}, "published": "2024-02-28T09:15:37.640", "references": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/07c9b834c97d0fa3402fb7f3f3b32df370a6ff1f"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/140cfd9980124aecb6c03ef2e69c72d0548744de"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/2d59a0ed8b26b8f3638d8afc31f839e27759f1f6"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/319116227e52d49eee671f0aa278bac89b3c1b69"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/7ed9d238c7dbb1fdb63ad96a6184985151b0171c"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/ad53127973034c63b5348715a1043d0e80ceb330"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/b3f1731c6d7fbc1ebe3ed8eff6d6bec56d76ff43"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/07c9b834c97d0fa3402fb7f3f3b32df370a6ff1f"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/140cfd9980124aecb6c03ef2e69c72d0548744de"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/2d59a0ed8b26b8f3638d8afc31f839e27759f1f6"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/319116227e52d49eee671f0aa278bac89b3c1b69"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/7ed9d238c7dbb1fdb63ad96a6184985151b0171c"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/ad53127973034c63b5348715a1043d0e80ceb330"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/b3f1731c6d7fbc1ebe3ed8eff6d6bec56d76ff43"}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "vulnStatus": "Undergoing Analysis", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-416"}], "source": "[email protected]", "type": "Primary"}]}

{"bugzilla": {"description": "kernel: userfaultfd: release page in error path to avoid BUG_ON", "id": "2266900", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2266900"}, "csaw": false, "cvss3": {"cvss3_base_score": "5.5", "cvss3_scoring_vector": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "status": "draft"}, "cwe": "CWE-416", "details": ["In the Linux kernel, the following vulnerability has been resolved:\nuserfaultfd: release page in error path to avoid BUG_ON\nConsider the following sequence of events:\n1. Userspace issues a UFFD ioctl, which ends up calling into\nshmem_mfill_atomic_pte(). We successfully account the blocks, we\nshmem_alloc_page(), but then the copy_from_user() fails. We return\n-ENOENT. We don't release the page we allocated.\n2. Our caller detects this error code, tries the copy_from_user() after\ndropping the mmap_lock, and retries, calling back into\nshmem_mfill_atomic_pte().\n3. Meanwhile, let's say another process filled up the tmpfs being used.\n4. So shmem_mfill_atomic_pte() fails to account blocks this time, and\nimmediately returns - without releasing the page.\nThis triggers a BUG_ON in our caller, which asserts that the page\nshould always be consumed, unless -ENOENT is returned.\nTo fix this, detect if we have such a \"dangling\" page when accounting\nfails, and if so, release it before returning."], "name": "CVE-2021-46988", "package_state": [{"cpe": "cpe:/o:redhat:enterprise_linux:6", "fix_state": "Out of support scope", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 6"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Out of support scope", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Out of support scope", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 9"}], "public_date": "2024-02-28T00:00:00Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2021-46988\nhttps://nvd.nist.gov/vuln/detail/CVE-2021-46988\nhttps://lore.kernel.org/linux-cve-announce/2024022825-CVE-2021-46988-ae47@gregkh/T/#u"], "threat_severity": "Low", "upstream_fix": "kernel 4.14.233, kernel 4.19.191, kernel 5.4.120, kernel 5.10.38, kernel 5.11.22, kernel 5.12.5, kernel 5.13"}