CVE-2026-80532 in Linux
Summary
by MITRE • 08/26/2026
In the Linux kernel, the following vulnerability has been resolved:
xfs: fix another iunlink infinite loop bug in online fsck
xrep_iunlink_resolve_bucket is supposed to reconstruct as much of the incore prev and next unlinked list pointers based on what it finds on disk and in memory before we move on to relinking the truly lost inodes back into the unlinked list. However, it's still vulnerable to infinite loops that come in via the next_unlinked pointers.
Fix this problem by remembering which inodes we've already seen and checking new agino pointers against that. If a bit is already set, either this is a loop or the inode has nonzero link count. We'll deal with the second case in a subsequent patch.
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Analysis
by VulDB Data Team • 08/26/2026
The XFS filesystem implementation within the Linux kernel contains a critical logic flaw in its online file system check utility, specifically affecting the unlinked inode list reconstruction process. The function xrep_iunlink_resolve_bucket is designed to rebuild the internal pointers that maintain the integrity of the unlinked inode chain, which tracks files that have been deleted but not yet fully removed from disk due to open handles or other pending operations. During this repair operation, the code attempts to reconstruct previous and next pointer values based on data found both in memory and directly on the storage medium before proceeding with relinking lost inodes. However, the existing validation logic fails to adequately detect cyclic references within these pointers, leaving the system vulnerable to infinite loops when processing corrupted or maliciously crafted filesystem metadata.
This vulnerability stems from a lack of state tracking during the traversal of the unlinked inode list. When resolving bucket entries, the algorithm iterates through inodes by following next_unlinked pointers without maintaining a record of previously visited nodes. If an attacker can manipulate disk structures to create a circular reference within this chain, or if filesystem corruption results in such a loop, the repair tool will enter an infinite execution cycle. This behavior effectively causes a denial of service condition for any system attempting to run online fsck operations on affected XFS volumes. The issue highlights a gap in defensive programming practices where iterative traversal over linked structures does not include cycle detection mechanisms appropriate for potentially untrusted or corrupted input data.
From a technical classification perspective, this flaw aligns with CWE-835, which describes the use of a loop counter that is never incremented correctly leading to an infinite loop, and more broadly falls under CWE-617 regarding reachability of assertion failure due to logic errors in state management. In terms of attack vectors, while primarily triggered by filesystem corruption or specific crafted disk images rather than direct user input execution, it represents a risk to system availability during maintenance operations. The ATT&CK framework categorizes such behaviors under techniques that impact resource availability, particularly those exploiting software vulnerabilities to cause service disruption without requiring authentication if the fsck tool is run automatically on boot or by administrative scripts.
The resolution involves implementing a mechanism to track visited inodes during the traversal process. By maintaining a set of already encountered inode numbers, the function can now detect when it encounters an agino pointer that has been seen before. This check allows the system to distinguish between legitimate circular references caused by corruption and valid non-zero link count scenarios where multiple hard links point to the same inode structure. Although this patch addresses the immediate infinite loop issue, it acknowledges that further refinement is required to properly handle cases involving nonzero link counts in subsequent updates. Administrators should ensure their systems are updated with kernel patches containing this fix to prevent potential hangs during filesystem consistency checks. Regular maintenance of XFS volumes and monitoring for signs of metadata corruption can mitigate exposure to such logic flaws until the full remediation path including the handling of complex linking scenarios is deployed.