Skip to content

In the Linux kernel, the following vulnerability has been...

Moderate severity Unreviewed Published Feb 28, 2024 to the GitHub Advisory Database • Updated Dec 24, 2024

Package

No package listed— Suggest a package

Affected versions

Unknown

Patched versions

Unknown

Description

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.

References

Published by the National Vulnerability Database Feb 28, 2024
Published to the GitHub Advisory Database Feb 28, 2024
Last updated Dec 24, 2024

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(5th percentile)

Weaknesses

CVE ID

CVE-2021-46988

GHSA ID

GHSA-w36p-947m-7c32

Source code

No known source code

Dependabot alerts are not supported on this advisory because it does not have a package from a supported ecosystem with an affected and fixed version.

Learn more about GitHub language support

Loading Checking history
See something to contribute? Suggest improvements for this vulnerability.