CVE-2025-40209

/// Technical description

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

btrfs: fix memory leak of qgroup_list in btrfs_add_qgroup_relation

When btrfs_add_qgroup_relation() is called with invalid qgroup levels

(src >= dst), the function returns -EINVAL directly without freeing the

preallocated qgroup_list structure passed by the caller. This causes a

memory leak because the caller unconditionally sets the pointer to NULL

after the call, preventing any cleanup.

The issue occurs because the level validation check happens before the

mutex is acquired and before any error handling path that would free

the prealloc pointer. On this early return, the cleanup code at the

'out' label (which includes kfree(prealloc)) is never reached.

In btrfs_ioctl_qgroup_assign(), the code pattern is:

prealloc = kzalloc(sizeof(*prealloc), GFP_KERNEL);

ret = btrfs_add_qgroup_relation(trans, sa->src, sa->dst, prealloc);

prealloc = NULL; // Always set to NULL regardless of return value

...

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/// 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