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

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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.

Fixes: 1d57628ff9 ("dm-pcache: add persistent cache target in device-mapper")
Cc: stable@vger.kernel.org
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

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This commit is contained in:

Bryam Vargas 2026-07-17 06:26:56 -05:00 • committed by Mikulas Patocka

parent 32d1809da3

commit f11deb032f

4 changed files with 38 additions and 9 deletions

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21

drivers/md/dm-pcache/cache.h

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8

drivers/md/dm-pcache/cache_gc.c

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10

drivers/md/dm-pcache/cache_key.c

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8

drivers/md/dm-pcache/cache_writeback.c

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