dm-pcache: validate geometry fields from on-disk cache_info

Overview

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

dm-pcache: validate geometry fields from on-disk cache_info

cache_segs_init() iterates cache_info->n_segs times indexing cache->segments[], which is sized to the cache device geometry, and get_seg_id() takes each segment id from the on-media cache_info and the per-segment next_seg link. Both come from cache device metadata that is only CRC-protected with a fixed public seed, so whoever supplies the cache device on a table load (CAP_SYS_ADMIN) controls them: an oversized n_segs or an out-of-range id drives an out-of-bounds access of cache->segments[] and a wild CACHE_DEV_SEGMENT() pointer into the device mapping -- an out-of-bounds read and write from on-disk data.

Reject an n_segs that exceeds the device segment count and a segment id that is out of range before either is used. Valid metadata is unaffected.

Affected

• Linux >= 1d57628ff95b32d5cfa8d8f50e07690c161e9cf0 < ab5dcde6fa96bc115b85f3621c60e39c66229a90
• Linux >= 1d57628ff95b32d5cfa8d8f50e07690c161e9cf0 < 3e19172089ec81132a8a48e802b1034a744209f4
• Linux >= 1d57628ff95b32d5cfa8d8f50e07690c161e9cf0 < 32d1809da31094ef76fd98dc1f1a8b55ca1295dd
• Linux 6.18

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

Vendor advisories

• Red Hat VEX · Moderate · updated 2026-09-14 · vex