dm-pcache: validate on-media seg_num against the cache device size

Overview

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

dm-pcache: validate on-media seg_num against the cache device size

seg_num is read from the crc32c-only superblock, so whoever supplies the cache device on a table load (CAP_SYS_ADMIN) controls it. It sizes cache->segments[] and is the value every later on-media segment id is bounded against, yet it is never checked against the device. Because cache_dev->mapping is the direct map of the pmem, CACHE_DEV_SEGMENT() for a segment id past the device resolves to ordinary kernel memory beyond the mapping; a new-cache init reaching such an id has cache_seg_init() -> cache_dev_zero_range() memset() 12 KiB over that memory -- an out-of-bounds write into the kernel heap at table load. A zero seg_num makes the segment allocations ZERO_SIZE_PTR.

Reject a seg_num that is zero, larger than the device can hold, or larger than PCACHE_CACHE_SEGS_MAX before it is used.

Affected

• Linux >= 1d57628ff95b32d5cfa8d8f50e07690c161e9cf0 < 91b93fe5cf4d62d5ecc642a6c8f15a3c11b00e3c
• Linux >= 1d57628ff95b32d5cfa8d8f50e07690c161e9cf0 < e889c0ee81165fc90aad2979b51f930f77895703
• Linux >= 1d57628ff95b32d5cfa8d8f50e07690c161e9cf0 < 62d92e45abe9e087370f9fc5d876b95673aced34
• 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