dm-pcache: validate kset key_num and intra-segment bounds

Overview

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

dm-pcache: validate kset key_num and intra-segment bounds

Two more fields decoded from the cache device go unbounded. The kset key_num drives cache_kset_crc() and the replay loop in cache_replay(), the writeback worker and the GC worker, but only the magic and a fixed-seed CRC are checked first, so a non-last kset whose key_num exceeds the PCACHE_KSET_KEYS_MAX buffer reads past its end before the CRC compare. A key's intra-segment offset and length in cache_key_decode() are taken verbatim, so a key running past its segment is replayed into the cache tree and the data CRC check and every later read hit then copy adjacent persistent memory into the caller's bio -- an out-of-bounds read that leaks to user space. Both fields are controlled by whoever supplies the cache device (CAP_SYS_ADMIN); the CRC seed is public.

Add kset_onmedia_valid() to bound key_num before any kset read, and reject a key whose offset plus length, computed in 64 bits, exceeds the segment data_size. Valid metadata is unaffected.

Affected

• Linux >= 1d57628ff95b32d5cfa8d8f50e07690c161e9cf0 < d8caf96040a06096276ab72f5e1e8547c014c564
• Linux >= 1d57628ff95b32d5cfa8d8f50e07690c161e9cf0 < 5ac38f4b4862fad6e7270fde5c3356a822ce74ca
• Linux >= 1d57628ff95b32d5cfa8d8f50e07690c161e9cf0 < f11deb032fd84081e7831cffcba895d893054a22
• Linux 6.18

Remediation

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

Vendor advisories

• Red Hat VEX · Moderate · updated 2026-10-17 · vex