CVE-2026-80958 in Linux
Summary
by MITRE • 09/11/2026
In the Linux kernel, the following vulnerability has been resolved:
dm-pcache: clamp the tail kset read to the segment data region
The tail-kset read in cache_replay(), the writeback worker and the GC worker bounds its length by PCACHE_SEG_SIZE - seg_off, the raw segment size rather than the data region. A tail near the segment end reads past the segment data into the following control area.
Clamp the read to cache_seg_remain(), the data region.
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Analysis
by VulDB Data Team • 09/11/2026
The Linux kernel device-mapper persistent cache subsystem contains a critical boundary check error within its internal management logic, specifically affecting how data segments are replayed and managed during writeback or garbage collection operations. This vulnerability stems from an incorrect calculation of read boundaries in functions such as cache_replay, the writeback worker, and the garbage collection worker. These components are responsible for maintaining the integrity and consistency of cached block device data by managing segment lifecycles and persisting state changes to disk. The core flaw lies in how these workers determine the extent of a tail kset read operation when processing segments that approach the end of their allocated storage space.
Technically, the defect involves using PCACHE_SEG_SIZE minus the segment offset as the limiting factor for read lengths. This calculation represents the raw total size of the physical segment rather than the usable data region within that segment. Device-mapper persistent cache structures typically divide each segment into a data area and a control or metadata area to store internal state information required for crash recovery and consistency checks. By failing to account for this division, the code permits read operations to extend beyond the designated data boundaries and intrude into the adjacent control area. This constitutes an out-of-bounds read vulnerability where memory that is reserved for system management purposes is accessed as if it were user or block device data.
The operational impact of this flaw can vary depending on whether the condition triggers a fault or allows silent corruption. In many kernel contexts, accessing unmapped or protected control regions results in a page fault leading to an immediate kernel panic and denial of service for the host system. However, if the memory layout permits access without triggering protection mechanisms, the consequence is more severe data integrity compromise. Reading into the control area may expose sensitive internal state information that could potentially be leveraged by local attackers to infer system configuration or bypass security controls. Furthermore, subsequent processing of this corrupted metadata can lead to logical errors in cache management, resulting in data loss or filesystem corruption for applications relying on the device-mapper layer.
This vulnerability aligns with CWE-125, which describes an out-of-bounds read error where software reads past the end of a buffer. It also relates to CWE-787, as improper boundary checks often lead to memory safety violations that can be exploited for arbitrary code execution if combined with other conditions such as use-after-free scenarios in adjacent subsystems. From a threat modeling perspective using MITRE ATT&CK, this flaw falls under the category of Defense Evasion or Discovery techniques where an attacker might exploit kernel memory leaks to gather intelligence about the host environment. The lack of strict boundary enforcement represents a fundamental failure in input validation and resource management within low-level storage drivers.
Mitigation strategies primarily involve applying vendor-provided kernel patches that correct the arithmetic logic to use cache_seg_remain instead of PCACHE_SEG_SIZE for determining read limits. This ensures that all operations are strictly confined to the valid data region, preserving the integrity of the control area. System administrators should prioritize updating their Linux kernels to versions where this fix is integrated, particularly in environments utilizing device-mapper persistent caching features such as dm-cache or similar storage virtualization layers. Additionally, enabling kernel hardening options like KASAN (Kernel Address Sanitizer) during development and testing phases can help detect such boundary violations early before they reach production systems. Regular auditing of storage driver code for proper buffer management practices is also recommended to prevent recurrence of similar memory safety issues in future updates.