ext4 crypto: add padding to filenames before encrypting

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>

1 files changed, 1 insertions, 0 deletions

diff --git a/fs/ext4/crypto_key.c b/fs/ext4/crypto_key.c
index c8392af8abbb..52170d0b7c40 100644
--- a/fs/ext4/crypto_key.c
+++ b/fs/ext4/crypto_key.c
@@ -110,6 +110,7 @@ int ext4_generate_encryption_key(struct inode *inode)
         }
         res = 0;
 
+        ei->i_crypt_policy_flags = ctx.flags;
         if (S_ISREG(inode->i_mode))
                 crypt_key->mode = ctx.contents_encryption_mode;
         else if (S_ISDIR(inode->i_mode) || S_ISLNK(inode->i_mode))