• Mikulas Patocka's avatar
    dm verity: fix inability to use a few specific devices sizes · dabd2582
    Mikulas Patocka authored
    commit b1bf2de07271932326af847a3c6a01fdfd29d4be upstream.
    
    Fix a boundary condition that caused failure for certain device sizes.
    
    The problem is reported at
      http://code.google.com/p/cryptsetup/issues/detail?id=160
    
    For certain device sizes the number of hashes at a specific level was
    calculated incorrectly.
    
    It happens for example for a device with data and metadata block size 4096
    that has 16385 blocks and algorithm sha256.
    
    The user can test if he is affected by this bug by running the
    "veritysetup verify" command and also by activating the dm-verity kernel
    driver and reading the whole block device. If it passes without an error,
    then the user is not affected.
    
    The condition for the bug is:
    
    Split the total number of data blocks (data_block_bits) into bit strings,
    each string has hash_per_block_bits bits. hash_per_block_bits is
    rounddown(log2(metadata_block_size/hash_digest_size)). Equivalently, you
    can say that you convert data_blocks_bits to 2^hash_per_block_bits base.
    
    If there some zero bit string below the most significant bit string and at
    least one bit below this zero bit string is set, then the bug happens.
    
    The same bug exists in the userspace veritysetup tool, so you must use
    fixed veritysetup too if you want to use devices that are affected by
    this boundary condition.
    Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
    Cc: Milan Broz <gmazyland@gmail.com>
    Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    dabd2582
dm-verity.c 22.9 KB