dm-integrity: replace forgeable discard filler with a keyed sector marker

In the Linux kernel, the following vulnerability has been resolved: dm-integrity: replace forgeable discard filler with a keyed sector marker The discard-block check in dm_integrity_rw_tag() treats a stored tag of all 0xf6 bytes (DISCARD_FILLER) as proof a block was discarded and skips HMAC verification. allow_discards is only accepted in dm-integrity's standalone mode. An attacker with raw write access to the backing device, but without the integrity key, can stamp any block with an all-0xf6 tag and have it served as authentic. Add a new "allow_discards_keyed" target argument that marks discarded blocks with a keyed checksum of (salt || sector) instead, computed by integrity_discard_checksum().

Where it's fixed