Description

In the Linux kernel, the following vulnerability has been resolved: gfs2: move quota_init qc iterator increment Move qc++ from the loop body into the for-loop increment expression in gfs2_quota_init(). This keeps iterator progression explicit and avoids mixing pointer advance with duplicate-slot handling in the loop body.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.1",
  "pubDate": "2026-09-24T17:17:30.050Z",
  "pubdate": "2026-09-24T17:17:30.050Z",
  "executiveSummary": "A logical vulnerability exists within the Linux kernel's GFS2 (Global File System 2) quota initialization process, specifically within the gfs2_quota_init function.\nThe flaw pertains to the improper management of the quota controller (qc) iterator, where the increment operation was incorrectly placed within the loop body rather than the for-loop header.\nThis design flaw introduces potential hazards related to memory access and iterator progression, particularly when handling duplicate quota slots. While primarily a code-correctness issue, inconsistencies in iterator progression can lead to memory corruption or undefined kernel behavior during filesystem initialization or mount operations.\nThe vulnerability affects systems utilizing the GFS2 filesystem module. Exploitation would likely require a local attacker to possess sufficient privileges to trigger filesystem mount or quota initialization sequences, potentially resulting in kernel crashes, denial-of-service conditions, or unpredictable filesystem state transitions.\nThe risk is mitigated by enforcing explicit iterator progression, ensuring that memory references remain within expected bounds during the processing of quota structures.",
  "technicalDetails": "The root cause of this vulnerability lies in the non-standard implementation of the loop control structure within the gfs2_quota_init function in the Linux kernel GFS2 implementation.\nIn the original implementation, the qc iterator increment (qc++) was embedded directly within the loop body. This practice is inherently error-prone, as it conflates the functional logic of the quota slot initialization with the administrative task of advancing the iterator pointer.\nWhen an iterator increment is manually placed within the loop body, logic branches—such as those handling duplicate-slot occurrences or error conditions—can lead to scenarios where the iterator is either incremented prematurely, incremented multiple times, or bypassed entirely. In C-based kernel code, failing to strictly govern pointer progression during iteration over a list or array can lead to off-by-one errors or out-of-bounds memory accesses.\nThe attack flow for this vulnerability involves an attacker triggering the gfs2_quota_init path through malicious or malformed filesystem metadata that force the kernel to handle specific quota slot conditions. If the iterator logic is inconsistent, the kernel may attempt to process memory outside the allocated scope for the quota structure or process the same slot incorrectly. This can cause kernel-mode segmentation faults (oops), leading to a system-wide denial-of-service.\nFurthermore, because this logic occurs during the initialization phase, the vulnerability effectively compromises the integrity of the filesystem's quota management subsystem. If the pointer arithmetic is influenced by the attacker's supplied metadata, it is theoretically possible to influence the state machine of the quota initialization, potentially leading to incorrect quota enforcement or memory corruption if the kernel's slab allocator is impacted by the malformed structures.\nThe fix involves moving the qc++ increment operation into the for-loop header. This transition ensures that the loop control mechanism remains robust, atomic, and independent of the specific logic applied to individual quota elements. By decoupling the iterator progression from the loop body, the kernel ensures that every iteration is handled consistently, thereby preventing logic errors when dealing with duplicate slots or complex internal GFS2 quota metadata."
}