CVE-2026-43338

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

btrfs: reserve enough transaction items for qgroup ioctls

Currently our qgroup ioctls don't reserve any space, they just do a

transaction join, which does not reserve any space, neither for the quota

tree updates nor for the delayed refs generated when updating the quota

tree. The quota root uses the global block reserve, which is fine most of

the time since we don't expect a lot of updates to the quota root, or to

be too close to -ENOSPC such that other critical metadata updates need to

resort to the global reserve.

However this is not optimal, as not reserving proper space may result in a

transaction abort due to not reserving space for delayed refs and then

abusing the use of the global block reserve.

For example, the following reproducer (which is unlikely to model any

real world use case, but just to illustrate the problem), triggers such a

transaction abort due to -ENOSPC when running delayed refs:

$ cat t

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References