[PATCH] Extract bch_crypt_update_passphrase function

[Mae Kasza <git@badat.dev>]

This also fixes a bug where the set-passphrase
command failed to derive the key for disks initially
formatted with --encrypted and --no_passphrase, due to
bch_sb_crypt_init not configuring the KDF params if
the passphrase wasn't specified during formatting.

Signed-off-by: Mae Kasza <git@badat.dev>
---
 c_src/cmd_key.c | 26 ++++++++++----------------
 c_src/crypto.c  | 43 ++++++++++++++++++++++++++++++++-----------
 c_src/crypto.h  |  3 +++
 3 files changed, 45 insertions(+), 27 deletions(-)

diff --git a/c_src/cmd_key.c b/c_src/cmd_key.c
index adb0ac8d..ac8a94a8 100644
--- a/c_src/cmd_key.c
+++ b/c_src/cmd_key.c
@@ -104,24 +104,19 @@ int cmd_set_passphrase(int argc, char *argv[])
 	if (IS_ERR(c))
 		die("Error opening %s: %s", argv[1], bch2_err_str(PTR_ERR(c)));
 
-	struct bch_sb_field_crypt *crypt = bch2_sb_field_get(c->disk_sb.sb, crypt);
+	struct bch_sb *sb = c->disk_sb.sb;
+	struct bch_sb_field_crypt *crypt = bch2_sb_field_get(sb, crypt);
 	if (!crypt)
 		die("Filesystem does not have encryption enabled");
 
-	struct bch_encrypted_key new_key;
-	new_key.magic = BCH_KEY_MAGIC;
-
-	int ret = bch2_decrypt_sb_key(c, crypt, &new_key.key);
+	struct bch_key key;
+	int ret = bch2_decrypt_sb_key(c, crypt, &key);
 	if (ret)
 		die("Error getting current key");
 
 	char *new_passphrase = read_passphrase_twice("Enter new passphrase: ");
-	struct bch_key passphrase_key = derive_passphrase(crypt, new_passphrase);
 
-	if (bch2_chacha_encrypt_key(&passphrase_key, __bch2_sb_key_nonce(c->disk_sb.sb),
-				    &new_key, sizeof(new_key)))
-		die("error encrypting key");
-	crypt->key = new_key;
+	bch_crypt_update_passphrase(sb, crypt, &key, new_passphrase);
 
 	bch2_revoke_key(c->disk_sb.sb);
 	bch2_write_super(c);
@@ -142,18 +137,17 @@ int cmd_remove_passphrase(int argc, char *argv[])
 	if (IS_ERR(c))
 		die("Error opening %s: %s", argv[1], bch2_err_str(PTR_ERR(c)));
 
-	struct bch_sb_field_crypt *crypt = bch2_sb_field_get(c->disk_sb.sb, crypt);
+	struct bch_sb *sb = c->disk_sb.sb;
+	struct bch_sb_field_crypt *crypt = bch2_sb_field_get(sb, crypt);
 	if (!crypt)
 		die("Filesystem does not have encryption enabled");
 
-	struct bch_encrypted_key new_key;
-	new_key.magic = BCH_KEY_MAGIC;
-
-	int ret = bch2_decrypt_sb_key(c, crypt, &new_key.key);
+	struct bch_key key;
+	int ret = bch2_decrypt_sb_key(c, crypt, &key);
 	if (ret)
 		die("Error getting current key");
 
-	crypt->key = new_key;
+	bch_crypt_update_passphrase(sb, crypt, &key, NULL);
 
 	bch2_write_super(c);
 	bch2_fs_stop(c);
diff --git a/c_src/crypto.c b/c_src/crypto.c
index 32671bd8..301dbebe 100644
--- a/c_src/crypto.c
+++ b/c_src/crypto.c
@@ -176,26 +176,47 @@ void bch_sb_crypt_init(struct bch_sb *sb,
 		       struct bch_sb_field_crypt *crypt,
 		       const char *passphrase)
 {
+	struct bch_key key;
+	get_random_bytes(&key, sizeof(key));
+
 	crypt->key.magic = BCH_KEY_MAGIC;
-	get_random_bytes(&crypt->key.key, sizeof(crypt->key.key));
+	crypt->key.key = key;
 
-	if (passphrase) {
+	bch_crypt_update_passphrase(sb, crypt, &key, passphrase);
+}
 
+void bch_crypt_update_passphrase(
+			struct bch_sb *sb,
+			struct bch_sb_field_crypt *crypt,
+			struct bch_key *key,
+			const char *new_passphrase)
+{
+
+	struct bch_encrypted_key new_key;
+	new_key.magic = BCH_KEY_MAGIC;
+	new_key.key = *key;
+
+	if(!new_passphrase) {
+		crypt->key = new_key;
+		return;
+	}
+
+	// If crypt already has an encrypted key reuse it's encryption params
+	if (!bch2_key_is_encrypted(&crypt->key)) {
 		SET_BCH_CRYPT_KDF_TYPE(crypt, BCH_KDF_SCRYPT);
 		SET_BCH_KDF_SCRYPT_N(crypt, ilog2(16384));
 		SET_BCH_KDF_SCRYPT_R(crypt, ilog2(8));
 		SET_BCH_KDF_SCRYPT_P(crypt, ilog2(16));
+	}
 
-		struct bch_key passphrase_key = derive_passphrase(crypt, passphrase);
-
-		assert(!bch2_key_is_encrypted(&crypt->key));
+	struct bch_key passphrase_key = derive_passphrase(crypt, new_passphrase);
 
-		if (bch2_chacha_encrypt_key(&passphrase_key, __bch2_sb_key_nonce(sb),
-					   &crypt->key, sizeof(crypt->key)))
-			die("error encrypting key");
+	if (bch2_chacha_encrypt_key(&passphrase_key, __bch2_sb_key_nonce(sb),
+				    &new_key, sizeof(new_key)))
+		die("error encrypting key");
 
-		assert(bch2_key_is_encrypted(&crypt->key));
+	memzero_explicit(&passphrase_key, sizeof(passphrase_key));
 
-		memzero_explicit(&passphrase_key, sizeof(passphrase_key));
-	}
+	crypt->key = new_key;
+	assert(bch2_key_is_encrypted(&crypt->key));
 }
diff --git a/c_src/crypto.h b/c_src/crypto.h
index baea6d86..cd3baac8 100644
--- a/c_src/crypto.h
+++ b/c_src/crypto.h
@@ -19,4 +19,7 @@ void bch2_add_key(struct bch_sb *, const char *, const char *, const char *);
 void bch_sb_crypt_init(struct bch_sb *sb, struct bch_sb_field_crypt *,
 		       const char *);
 
+void bch_crypt_update_passphrase(struct bch_sb *sb, struct bch_sb_field_crypt *crypt,
+			struct bch_key *key, const char *new_passphrase);
+
 #endif /* _CRYPTO_H */
-- 
2.45.2