CVE-2021-46988
userfaultfd: release page in error path to avoid BUG_ON
Severity Score
Exploit Likelihood
Affected Versions
Public Exploits
0Exploited in Wild
-Decision
Descriptions
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.
En el kernel de Linux, se resolvió la siguiente vulnerabilidad: userfaultfd: publicar página 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 éxito los bloques, usamos shmem_alloc_page(), pero luego copy_from_user() falla. Volvemos -ENOENT. No publicamos la página que asignamos. 2. Nuestra persona que llama detecta este código de error, intenta copiar_from_user() después de descartar mmap_lock y vuelve a intentarlo, volviendo a llamar a shmem_mfill_atomic_pte(). 3. Mientras tanto, digamos que otro proceso llenó 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 página. Esto desencadena un BUG_ON en nuestra persona que llama, que afirma que la página siempre debe consumirse, a menos que se devuelva -ENOENT. Para solucionar este problema, detectar si tenemos esa página "colgante" cuando falla la contabilidad y, en caso afirmativo, liberarla antes de regresar.
CVSS Scores
SSVC
- Decision:Track
Timeline
- 2024-02-27 CVE Reserved
- 2024-02-28 CVE Published
- 2024-02-29 EPSS Updated
- 2024-12-19 CVE Updated
- ---------- Exploited in Wild
- ---------- KEV Due Date
- ---------- First Exploit
CWE
CAPEC
References (8)
URL | Tag | Source |
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https://git.kernel.org/stable/c/cb658a453b9327ce96ce5222c24d162b5b65b564 | Vuln. Introduced |
URL | Date | SRC |
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URL | Date | SRC |
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Affected Vendors, Products, and Versions
Vendor | Product | Version | Other | Status | ||||||
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Vendor | Product | Version | Other | Status | <-- --> | Vendor | Product | Version | Other | Status |
Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.11 < 4.14.233 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.11 < 4.14.233" | en |
Affected
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Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.11 < 4.19.191 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.11 < 4.19.191" | en |
Affected
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Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.11 < 5.4.120 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.11 < 5.4.120" | en |
Affected
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Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.11 < 5.10.38 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.11 < 5.10.38" | en |
Affected
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Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.11 < 5.11.22 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.11 < 5.11.22" | en |
Affected
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Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.11 < 5.12.5 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.11 < 5.12.5" | en |
Affected
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Linux Search vendor "Linux" | Linux Kernel Search vendor "Linux" for product "Linux Kernel" | >= 4.11 < 5.13 Search vendor "Linux" for product "Linux Kernel" and version " >= 4.11 < 5.13" | en |
Affected
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