CVE-2026-80807 in Linux
Summary
by MITRE • 09/04/2026
In the Linux kernel, the following vulnerability has been resolved:
nilfs2: reject invalid block index in GC ioctl
Syzbot reported list corruption caused by a double list_add_tail() call on bh->b_assoc_buffers within nilfs_lookup_dirty_data_buffers().
Analysis revealed that the root cause was the insertion of a page/folio with a page index of ULONG_MAX into the page cache via the GC ioctl. filemap_get_folios_tag(), called by nilfs_lookup_dirty_data_buffers(), repeatedly detects a dirty folio with a page index of ULONG_MAX due to index wrap-around, leading to duplicate processing of dirty buffers.
As a preparatory step, the GC ioctl loads the page/folio of the block to be moved during GC and inserts it into the page cache based on information in the nilfs_vdesc structure passed as an argument. Normally, this does not cause issues because the user-space GC library configures the nilfs_vdesc structure properly. However, since there is no range check on the parameters determining the page index, a request with artificially crafted parameters -- such as those generated by Syzbot -- can result in a page/folio being inserted with a page index of ULONG_MAX, triggering the above problem.
This resolves the issue by checking the ranges of 'vd_offset' and 'vd_vblocknr' in the nilfs_vdesc structure that determine the page index, thereby preventing the invalid page/folio insertions.
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Analysis
by VulDB Data Team • 09/04/2026
The Linux kernel vulnerability identified within the NILFS2 filesystem driver involves a critical input validation failure during garbage collection operations initiated via ioctl calls. This flaw allows user-space applications to supply crafted parameters that result in the insertion of pages or folios with an invalid block index, specifically ULONG_MAX, into the page cache. The root cause lies in the absence of range checks on the vd_offset and vd_vblocknr fields within the nilfs_vdesc structure passed by userspace. While normal operation relies on well-behaved user-space libraries to configure these parameters correctly, malicious or buggy inputs can bypass this assumption, leading to severe memory corruption issues such as list corruption caused by double additions to buffer heads associated with dirty data buffers.
From a technical perspective, the vulnerability manifests when filemap_get_folios_tag is invoked during nilfs_lookup_dirty_data_buffers. This function iterates through folio tags and detects dirty entries based on their page index. When an invalid page index of ULONG_MAX is inserted due to integer wrap-around or lack of bounds checking, the iteration logic encounters this anomalous entry repeatedly. Consequently, the system attempts to process the same dirty buffers multiple times, triggering a double list_add_tail operation. This results in linked list corruption within the kernel's memory management subsystems, which can lead to unpredictable behavior including crashes, data loss, or potential privilege escalation if an attacker can exploit the corrupted state to overwrite critical kernel structures.
The operational impact of this vulnerability is significant as it affects system stability and integrity during filesystem maintenance operations. Garbage collection in NILFS2 involves moving blocks between segments, a process that requires careful management of page cache entries. By allowing invalid indices, attackers or faulty software can destabilize the kernel's internal data structures. This aligns with CWE-20 Improper Input Validation, as the system fails to verify that inputs fall within expected bounds before processing them. Furthermore, the exploitation vector relates to local privilege escalation through improper handling of ioctl arguments, which may be categorized under ATT&CK technique T1068 Exploitation for Privilege Escalation if leveraged in conjunction with other vulnerabilities to gain higher-level access.
Mitigation strategies primarily involve applying kernel patches that enforce strict range validation on the vd_offset and vd_vblocknr parameters within the nilfs_vdesc structure before any page cache operations are performed. System administrators should ensure their systems are updated with the latest stable kernels containing this fix. Additionally, developers integrating NILFS2 into applications must implement robust input sanitization to prevent passing out-of-bounds values to kernel interfaces. Regular auditing of ioctl handlers for similar validation gaps is recommended to maintain overall system security posture against local exploitation attempts targeting filesystem drivers.