Use After Free Affecting kernel-doc package, versions *


Severity

Recommended
low

Based on CentOS security rating.

Threat Intelligence

EPSS
0.04% (12th percentile)

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  • Snyk IDSNYK-CENTOS7-KERNELDOC-6329151
  • published29 Feb 2024
  • disclosed28 Feb 2024

Introduced: 28 Feb 2024

CVE-2021-46988  (opens in a new tab)
CWE-416  (opens in a new tab)
First added by Snyk

How to fix?

There is no fixed version for Centos:7 kernel-doc.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel-doc package and not the kernel-doc package as distributed by Centos. See How to fix? for Centos:7 relevant fixed versions and status.

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.

CVSS Scores

version 3.1