• Theodore Ts'o's avatar
    ext4 crypto: reorganize how we store keys in the inode · b7236e21
    Theodore Ts'o authored
    This is a pretty massive patch which does a number of different things:
    
    1) The per-inode encryption information is now stored in an allocated
       data structure, ext4_crypt_info, instead of directly in the node.
       This reduces the size usage of an in-memory inode when it is not
       using encryption.
    
    2) We drop the ext4_fname_crypto_ctx entirely, and use the per-inode
       encryption structure instead.  This remove an unnecessary memory
       allocation and free for the fname_crypto_ctx as well as allowing us
       to reuse the ctfm in a directory for multiple lookups and file
       creations.
    
    3) We also cache the inode's policy information in the ext4_crypt_info
       structure so we don't have to continually read it out of the
       extended attributes.
    
    4) We now keep the keyring key in the inode's encryption structure
       instead of releasing it after we are done using it to derive the
       per-inode key.  This allows us to test to see if the key has been
       revoked; if it has, we prevent the use of the derived key and free
       it.
    
    5) When an inode is released (or when the derived key is freed), we
       will use memset_explicit() to zero out the derived key, so it's not
       left hanging around in memory.  This implies that when a user logs
       out, it is important to first revoke the key, and then unlink it,
       and then finally, to use "echo 3 > /proc/sys/vm/drop_caches" to
       release any decrypted pages and dcache entries from the system
       caches.
    
    6) All this, and we also shrink the number of lines of code by around
       100.  :-)
    Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
    b7236e21
crypto_fname.c 12.8 KB