ext4 crypto: reorganize how we store keys in the inode

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  This allows us to test to see if the key has been
   revoked; if it has, we prevent the use of the derived key and free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>

1 files changed, 42 insertions, 34 deletions

diff --git a/fs/ext4/crypto_policy.c b/fs/ext4/crypto_policy.c
index a6d6291aea16..370d3aa0a9cf 100644
--- a/fs/ext4/crypto_policy.c
+++ b/fs/ext4/crypto_policy.c
@@ -126,7 +126,7 @@ int ext4_get_policy(struct inode *inode, struct ext4_encryption_policy *policy)
 int ext4_is_child_context_consistent_with_parent(struct inode *parent,
 						 struct inode *child)
 {
-	struct ext4_encryption_context parent_ctx, child_ctx;
+	struct ext4_crypt_info *parent_ci, *child_ci;
 	int res;
 
 	if ((parent == NULL) || (child == NULL)) {
@@ -136,26 +136,28 @@ int ext4_is_child_context_consistent_with_parent(struct inode *parent,
 	/* no restrictions if the parent directory is not encrypted */
 	if (!ext4_encrypted_inode(parent))
 		return 1;
-	res = ext4_xattr_get(parent, EXT4_XATTR_INDEX_ENCRYPTION,
-			     EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
-			     &parent_ctx, sizeof(parent_ctx));
-	if (res != sizeof(parent_ctx))
-		return 0;
 	/* if the child directory is not encrypted, this is always a problem */
 	if (!ext4_encrypted_inode(child))
 		return 0;
-	res = ext4_xattr_get(child, EXT4_XATTR_INDEX_ENCRYPTION,
-			     EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
-			     &child_ctx, sizeof(child_ctx));
-	if (res != sizeof(child_ctx))
+	res = ext4_get_encryption_info(parent);
+	if (res)
+		return 0;
+	res = ext4_get_encryption_info(child);
+	if (res)
+		return 0;
+	parent_ci = EXT4_I(parent)->i_crypt_info;
+	child_ci = EXT4_I(child)->i_crypt_info;
+	if (!parent_ci && !child_ci)
+		return 1;
+	if (!parent_ci || !child_ci)
 		return 0;
-	return (memcmp(parent_ctx.master_key_descriptor,
-		       child_ctx.master_key_descriptor,
+
+	return (memcmp(parent_ci->ci_master_key,
+		       child_ci->ci_master_key,
 		       EXT4_KEY_DESCRIPTOR_SIZE) == 0 &&
-		(parent_ctx.contents_encryption_mode ==
-		 child_ctx.contents_encryption_mode) &&
-		(parent_ctx.filenames_encryption_mode ==
-		 child_ctx.filenames_encryption_mode));
+		(parent_ci->ci_data_mode == child_ci->ci_data_mode) &&
+		(parent_ci->ci_filename_mode == child_ci->ci_filename_mode) &&
+		(parent_ci->ci_flags == child_ci->ci_flags));
 }
 
 /**
@@ -168,31 +170,37 @@ int ext4_is_child_context_consistent_with_parent(struct inode *parent,
 int ext4_inherit_context(struct inode *parent, struct inode *child)
 {
 	struct ext4_encryption_context ctx;
-	int res = ext4_xattr_get(parent, EXT4_XATTR_INDEX_ENCRYPTION,
-				 EXT4_XATTR_NAME_ENCRYPTION_CONTEXT,
-				 &ctx, sizeof(ctx));
+	struct ext4_crypt_info *ci;
+	int res;
+
+	res = ext4_get_encryption_info(parent);
+	if (res < 0)
+		return res;
+	ci = EXT4_I(parent)->i_crypt_info;
+	BUG_ON(ci == NULL);
 
-	if (res != sizeof(ctx)) {
-		if (DUMMY_ENCRYPTION_ENABLED(EXT4_SB(parent->i_sb))) {
-			ctx.format = EXT4_ENCRYPTION_CONTEXT_FORMAT_V1;
-			ctx.contents_encryption_mode =
-				EXT4_ENCRYPTION_MODE_AES_256_XTS;
-			ctx.filenames_encryption_mode =
-				EXT4_ENCRYPTION_MODE_AES_256_CTS;
-			ctx.flags = 0;
-			memset(ctx.master_key_descriptor, 0x42,
-			       EXT4_KEY_DESCRIPTOR_SIZE);
-			res = 0;
-		} else {
-			goto out;
-		}
+	ctx.format = EXT4_ENCRYPTION_CONTEXT_FORMAT_V1;
+	if (DUMMY_ENCRYPTION_ENABLED(EXT4_SB(parent->i_sb))) {
+		ctx.contents_encryption_mode = EXT4_ENCRYPTION_MODE_AES_256_XTS;
+		ctx.filenames_encryption_mode =
+			EXT4_ENCRYPTION_MODE_AES_256_CTS;
+		ctx.flags = 0;
+		memset(ctx.master_key_descriptor, 0x42,
+		       EXT4_KEY_DESCRIPTOR_SIZE);
+		res = 0;
+	} else {
+		ctx.contents_encryption_mode = ci->ci_data_mode;
+		ctx.filenames_encryption_mode = ci->ci_filename_mode;
+		ctx.flags = ci->ci_flags;
+		memcpy(ctx.master_key_descriptor, ci->ci_master_key,
+		       EXT4_KEY_DESCRIPTOR_SIZE);
 	}
 	get_random_bytes(ctx.nonce, EXT4_KEY_DERIVATION_NONCE_SIZE);
 	res = ext4_xattr_set(child, EXT4_XATTR_INDEX_ENCRYPTION,
 			     EXT4_XATTR_NAME_ENCRYPTION_CONTEXT, &ctx,
 			     sizeof(ctx), 0);
-out:
 	if (!res)
 		ext4_set_inode_flag(child, EXT4_INODE_ENCRYPT);
 	return res;
+
 }