fscrypt: remove internal key size constants

With one exception, the internal key size constants such as
FS_AES_256_XTS_KEY_SIZE are only used for the 'available_modes' array,
where they really only serve to obfuscate what the values are.  Also
some of the constants are unused, and the key sizes tend to be in the
names of the algorithms anyway.  In the past these values were also
misused, e.g. we used to have FS_AES_256_XTS_KEY_SIZE in places that
technically should have been FS_MAX_KEY_SIZE.

The exception is that FS_AES_128_ECB_KEY_SIZE is used for key
derivation.  But it's more appropriate to use
FS_KEY_DERIVATION_NONCE_SIZE for that instead.

Thus, just put the sizes directly in the 'available_modes' array.
Signed-off-by: NEric Biggers <ebiggers@google.com>
Signed-off-by: NTheodore Ts'o <tytso@mit.edu>

fs/crypto/fscrypt_private.h

@@ -18,15 +18,7 @@
 
 /* Encryption parameters */
 #define FS_IV_SIZE			16
-#define FS_AES_128_ECB_KEY_SIZE		16
-#define FS_AES_128_CBC_KEY_SIZE		16
-#define FS_AES_128_CTS_KEY_SIZE		16
-#define FS_AES_256_GCM_KEY_SIZE		32
-#define FS_AES_256_CBC_KEY_SIZE		32
-#define FS_AES_256_CTS_KEY_SIZE		32
-#define FS_AES_256_XTS_KEY_SIZE		64
-
-#define FS_KEY_DERIVATION_NONCE_SIZE		16
+#define FS_KEY_DERIVATION_NONCE_SIZE	16
 
 /**
  * Encryption context for inode

fs/crypto/keyinfo.c

@@ -27,7 +27,7 @@ static struct crypto_shash *essiv_hash_tfm;
  *
  * Return: Zero on success; non-zero otherwise.
  */
-static int derive_key_aes(u8 deriving_key[FS_AES_128_ECB_KEY_SIZE],
+static int derive_key_aes(u8 deriving_key[FS_KEY_DERIVATION_NONCE_SIZE],
 				const struct fscrypt_key *source_key,
 				u8 derived_raw_key[FS_MAX_KEY_SIZE])
 {
@@ -52,7 +52,7 @@ static int derive_key_aes(u8 deriving_key[FS_AES_128_ECB_KEY_SIZE],
 			CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 			crypto_req_done, &wait);
 	res = crypto_skcipher_setkey(tfm, deriving_key,
-					FS_AES_128_ECB_KEY_SIZE);
+				     FS_KEY_DERIVATION_NONCE_SIZE);
 	if (res < 0)
 		goto out;
 
@@ -100,7 +100,6 @@ static int validate_user_key(struct fscrypt_info *crypt_info,
 		goto out;
 	}
 	master_key = (struct fscrypt_key *)ukp->data;
-	BUILD_BUG_ON(FS_AES_128_ECB_KEY_SIZE != FS_KEY_DERIVATION_NONCE_SIZE);
 
 	if (master_key->size < min_keysize || master_key->size > FS_MAX_KEY_SIZE
 	    || master_key->size % AES_BLOCK_SIZE != 0) {
@@ -121,14 +120,10 @@ static const struct {
 	const char *cipher_str;
 	int keysize;
 } available_modes[] = {
-	[FS_ENCRYPTION_MODE_AES_256_XTS] = { "xts(aes)",
-					     FS_AES_256_XTS_KEY_SIZE },
-	[FS_ENCRYPTION_MODE_AES_256_CTS] = { "cts(cbc(aes))",
-					     FS_AES_256_CTS_KEY_SIZE },
-	[FS_ENCRYPTION_MODE_AES_128_CBC] = { "cbc(aes)",
-					     FS_AES_128_CBC_KEY_SIZE },
-	[FS_ENCRYPTION_MODE_AES_128_CTS] = { "cts(cbc(aes))",
-					     FS_AES_128_CTS_KEY_SIZE },
+	[FS_ENCRYPTION_MODE_AES_256_XTS]      = { "xts(aes)",		64 },
+	[FS_ENCRYPTION_MODE_AES_256_CTS]      = { "cts(cbc(aes))",	32 },
+	[FS_ENCRYPTION_MODE_AES_128_CBC]      = { "cbc(aes)",		16 },
+	[FS_ENCRYPTION_MODE_AES_128_CTS]      = { "cts(cbc(aes))",	16 },
 };
 
 static int determine_cipher_type(struct fscrypt_info *ci, struct inode *inode,