fix(core/stellar): review usages of write_bytes_unchecked

(cherry picked from commit 781e9f4db8)

core/src/apps/stellar/operations/serialize.py

@@ -119,7 +119,7 @@ def write_set_options_op(w, msg: StellarSetOptionsOp):
     elif msg.signer_type in consts.SIGN_TYPES:
         writers.write_bool(w, True)
         writers.write_uint32(w, msg.signer_type)
-        writers.write_bytes_unchecked(w, msg.signer_key)
+        writers.write_bytes_fixed(w, msg.signer_key, 32)
         writers.write_uint32(w, msg.signer_weight)
     else:
         raise ProcessError("Stellar: unknown signer type")
@@ -146,10 +146,10 @@ def _write_asset_code(w, asset_type: int, asset_code: str):
         return  # nothing is needed
     elif asset_type == consts.ASSET_TYPE_ALPHANUM4:
         # pad with zeros to 4 chars
-        writers.write_bytes_unchecked(w, code + bytearray([0] * (4 - len(code))))
+        writers.write_bytes_fixed(w, code + bytearray([0] * (4 - len(code))), 4)
     elif asset_type == consts.ASSET_TYPE_ALPHANUM12:
         # pad with zeros to 12 chars
-        writers.write_bytes_unchecked(w, code + bytearray([0] * (12 - len(code))))
+        writers.write_bytes_fixed(w, code + bytearray([0] * (12 - len(code))), 12)
     else:
         raise ProcessError("Stellar: invalid asset type")
 

core/src/apps/stellar/sign_tx.py

@@ -48,8 +48,8 @@ async def _final(ctx, w: bytearray, msg: StellarSignTx):
 
 async def _init(ctx, w: bytearray, pubkey: bytes, msg: StellarSignTx):
     network_passphrase_hash = sha256(msg.network_passphrase).digest()
-    writers.write_bytes_unchecked(w, network_passphrase_hash)
-    writers.write_bytes_unchecked(w, consts.TX_TYPE)
+    writers.write_bytes_fixed(w, network_passphrase_hash, 32)
+    writers.write_bytes_fixed(w, consts.TX_TYPE, 4)
 
     address = helpers.address_from_public_key(pubkey)
     accounts_match = msg.source_account == address
@@ -104,7 +104,7 @@ async def _memo(ctx, w: bytearray, msg: StellarSignTx):
         memo_confirm_text = str(msg.memo_id)
     elif msg.memo_type in (consts.MEMO_TYPE_HASH, consts.MEMO_TYPE_RETURN):
         # Hash/Return: 32 byte hash
-        writers.write_bytes_unchecked(w, bytearray(msg.memo_hash))
+        writers.write_bytes_fixed(w, bytearray(msg.memo_hash), 32)
         memo_confirm_text = hexlify(msg.memo_hash).decode()
     else:
         raise ProcessError("Stellar invalid memo type")

core/src/apps/stellar/writers.py

@@ -1,4 +1,9 @@
-from apps.common.writers import write_bytes_unchecked, write_uint32_be, write_uint64_be
+from apps.common.writers import (
+    write_bytes_fixed,
+    write_bytes_unchecked,
+    write_uint32_be,
+    write_uint64_be,
+)
 
 from .helpers import public_key_from_address
 
@@ -18,9 +23,9 @@ def write_string(w, s: AnyStr) -> None:
     write_uint32(w, len(buf))
     write_bytes_unchecked(w, buf)
     # if len isn't a multiple of 4, add padding bytes
-    reminder = len(buf) % 4
-    if reminder:
-        write_bytes_unchecked(w, bytes([0] * (4 - reminder)))
+    remainder = len(buf) % 4
+    if remainder:
+        write_bytes_unchecked(w, bytes([0] * (4 - remainder)))
 
 
 def write_bool(w, val: bool):
@@ -33,4 +38,4 @@ def write_bool(w, val: bool):
 def write_pubkey(w, address: str):
     # first 4 bytes of an address are the type, there's only one type (0)
     write_uint32(w, 0)
-    write_bytes_unchecked(w, public_key_from_address(address))
+    write_bytes_fixed(w, public_key_from_address(address), 32)