ext4 crypto: add ext4 encryption facilities

On encrypt, we will re-assign the buffer_heads to point to a bounce
page rather than the control_page (which is the original page to write
that contains the plaintext). The block I/O occurs against the bounce
page.  On write completion, we re-assign the buffer_heads to the
original plaintext page.

On decrypt, we will attach a read completion callback to the bio
struct. This read completion will decrypt the read contents in-place
prior to setting the page up-to-date.

The current encryption mode, AES-256-XTS, lacks cryptographic
integrity. AES-256-GCM is in-plan, but we will need to devise a
mechanism for handling the integrity data.

Signed-off-by: Michael Halcrow <mhalcrow@google.com>
Signed-off-by: Ildar Muslukhov <ildarm@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 8 insertions, 0 deletions

diff --git a/fs/ext4/crypto_policy.c b/fs/ext4/crypto_policy.c
index 532b69c0afab..a4bf762b3ba9 100644
--- a/fs/ext4/crypto_policy.c
+++ b/fs/ext4/crypto_policy.c
@@ -52,6 +52,13 @@ static int ext4_create_encryption_context_from_policy(
 	ctx.format = EXT4_ENCRYPTION_CONTEXT_FORMAT_V1;
 	memcpy(ctx.master_key_descriptor, policy->master_key_descriptor,
 	       EXT4_KEY_DESCRIPTOR_SIZE);
+	if (!ext4_valid_contents_enc_mode(policy->contents_encryption_mode)) {
+		printk(KERN_WARNING
+		       "%s: Invalid contents encryption mode %d\n", __func__,
+			policy->contents_encryption_mode);
+		res = -EINVAL;
+		goto out;
+	}
 	ctx.contents_encryption_mode = policy->contents_encryption_mode;
 	ctx.filenames_encryption_mode = policy->filenames_encryption_mode;
 	BUILD_BUG_ON(sizeof(ctx.nonce) != EXT4_KEY_DERIVATION_NONCE_SIZE);
@@ -60,6 +67,7 @@ static int ext4_create_encryption_context_from_policy(
 	res = ext4_xattr_set(inode, EXT4_XATTR_INDEX_ENCRYPTION,
 			     EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
 			     sizeof(ctx), 0);
+out:
 	if (!res)
 		ext4_set_inode_flag(inode, EXT4_INODE_ENCRYPT);
 	return res;