As suggested by Herbert Xu, we shouldn't allocate a new tfm each time
we read or write a page. Instead we can use a single tfm hanging off
the inode's crypt_info structure for all of our encryption needs for
that inode, since the tfm can be used by multiple crypto requests in
parallel.
Also use cmpxchg() to avoid races that could result in crypt_info
structure getting doubly allocated or doubly freed.
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
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 This allows us to test to see if the key has been
revoked; if it has, we prevent the use of the derived key and free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: Theodore Ts'o <tytso@mit.edu>
Use struct ext4_encryption_key only for the master key passed via the
kernel keyring.
For internal kernel space users, we now use struct ext4_crypt_info.
This will allow us to put information from the policy structure so we
can cache it and avoid needing to constantly looking up the extended
attribute. We will do this in a spearate patch. This patch is mostly
mechnical to make it easier for patch review.
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Encrypt the filename as soon it is passed in by the user. This avoids
our needing to encrypt the filename 2 or 3 times while in the process
of creating a filename.
Similarly, when looking up a directory entry, encrypt the filename
early, or if the encryption key is not available, base-64 decode the
file syystem so that the hash value and the last 16 bytes of the
encrypted filename is available in the new struct ext4_filename data
structure.
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This obscures the length of the filenames, to decrease the amount of
information leakage. By default, we pad the filenames to the next 4
byte boundaries. This costs nothing, since the directory entries are
aligned to 4 byte boundaries anyway. Filenames can also be padded to
8, 16, or 32 bytes, which will consume more directory space.
Change-Id: Ibb7a0fb76d2c48e2061240a709358ff40b14f322
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Avoid using SHA-1 when calculating the user-visible filename when the
encryption key is available, and avoid decrypting lots of filenames
when searching for a directory entry in a directory block.
Change-Id: If4655f144784978ba0305b597bfa1c8d7bb69e63
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
