use safe arithmetic wherever gas calculations can cause U256 to overflow

src/ethereum/frontier/vm/instructions/environment.py

@@ -15,8 +15,10 @@
 from ethereum.base_types import U256, Uint
 from ethereum.frontier.state import get_account
 from ethereum.frontier.utils.address import to_address
+from ethereum.frontier.vm.error import OutOfGasError
 from ethereum.frontier.vm.memory import extend_memory, memory_write
 from ethereum.utils.numeric import ceil32
+from ethereum.utils.safe_arithmetic import u256_safe_add, u256_safe_multiply
 
 from .. import Evm
 from ..gas import (
@@ -202,12 +204,21 @@ def calldatacopy(evm: Evm) -> None:
     size = pop(evm.stack)
 
     words = ceil32(Uint(size)) // 32
-    gas_cost = (
-        GAS_VERY_LOW
-        + (GAS_COPY * words)
-        + calculate_gas_extend_memory(evm.memory, memory_start_index, size)
+    copy_gas_cost = u256_safe_multiply(
+        GAS_COPY,
+        words,
+        exception_type=OutOfGasError,
     )
-    evm.gas_left = subtract_gas(evm.gas_left, gas_cost)
+    memory_extend_gas_cost = calculate_gas_extend_memory(
+        evm.memory, memory_start_index, size
+    )
+    total_gas_cost = u256_safe_add(
+        GAS_VERY_LOW,
+        copy_gas_cost,
+        memory_extend_gas_cost,
+        exception_type=OutOfGasError,
+    )
+    evm.gas_left = subtract_gas(evm.gas_left, total_gas_cost)
 
     if size == 0:
         return
@@ -264,12 +275,21 @@ def codecopy(evm: Evm) -> None:
     size = pop(evm.stack)
 
     words = ceil32(Uint(size)) // 32
-    gas_cost = (
-        GAS_VERY_LOW
-        + (GAS_COPY * words)
-        + calculate_gas_extend_memory(evm.memory, memory_start_index, size)
+    copy_gas_cost = u256_safe_multiply(
+        GAS_COPY,
+        words,
+        exception_type=OutOfGasError,
+    )
+    memory_extend_gas_cost = calculate_gas_extend_memory(
+        evm.memory, memory_start_index, size
     )
-    evm.gas_left = subtract_gas(evm.gas_left, gas_cost)
+    total_gas_cost = u256_safe_add(
+        GAS_VERY_LOW,
+        copy_gas_cost,
+        memory_extend_gas_cost,
+        exception_type=OutOfGasError,
+    )
+    evm.gas_left = subtract_gas(evm.gas_left, total_gas_cost)
 
     if size == 0:
         return
@@ -355,12 +375,21 @@ def extcodecopy(evm: Evm) -> None:
     size = pop(evm.stack)
 
     words = ceil32(Uint(size)) // 32
-    gas_cost = (
-        GAS_EXTERNAL
-        + (GAS_COPY * words)
-        + calculate_gas_extend_memory(evm.memory, memory_start_index, size)
+    copy_gas_cost = u256_safe_multiply(
+        GAS_COPY,
+        words,
+        exception_type=OutOfGasError,
+    )
+    memory_extend_gas_cost = calculate_gas_extend_memory(
+        evm.memory, memory_start_index, size
+    )
+    total_gas_cost = u256_safe_add(
+        GAS_EXTERNAL,
+        copy_gas_cost,
+        memory_extend_gas_cost,
+        exception_type=OutOfGasError,
     )
-    evm.gas_left = subtract_gas(evm.gas_left, gas_cost)
+    evm.gas_left = subtract_gas(evm.gas_left, total_gas_cost)
 
     if size == 0:
         return

src/ethereum/frontier/vm/instructions/keccak.py

@@ -14,7 +14,9 @@
 
 from ethereum.base_types import U256, Uint
 from ethereum.crypto import keccak256
+from ethereum.frontier.vm.error import OutOfGasError
 from ethereum.utils.numeric import ceil32
+from ethereum.utils.safe_arithmetic import u256_safe_add, u256_safe_multiply
 
 from .. import Evm
 from ..gas import (
@@ -50,12 +52,21 @@ def keccak(evm: Evm) -> None:
     size = pop(evm.stack)
 
     words = ceil32(Uint(size)) // 32
-    gas_cost = (
-        GAS_KECCAK256
-        + (GAS_KECCAK256_WORD * words)
-        + calculate_gas_extend_memory(evm.memory, memory_start_index, size)
+    word_gas_cost = u256_safe_multiply(
+        GAS_KECCAK256_WORD,
+        words,
+        exception_type=OutOfGasError,
     )
-    evm.gas_left = subtract_gas(evm.gas_left, gas_cost)
+    memory_extend_gas_cost = calculate_gas_extend_memory(
+        evm.memory, memory_start_index, size
+    )
+    total_gas_cost = u256_safe_add(
+        GAS_KECCAK256,
+        word_gas_cost,
+        memory_extend_gas_cost,
+        exception_type=OutOfGasError,
+    )
+    evm.gas_left = subtract_gas(evm.gas_left, total_gas_cost)
 
     extend_memory(evm.memory, memory_start_index, size)
 

src/ethereum/frontier/vm/instructions/memory.py

@@ -12,6 +12,8 @@
 Implementations of the EVM Memory instructions.
 """
 from ethereum.base_types import U8_MAX_VALUE, U256, Uint
+from ethereum.frontier.vm.error import OutOfGasError
+from ethereum.utils.safe_arithmetic import u256_safe_add
 
 from .. import Evm
 from ..gas import (
@@ -47,9 +49,13 @@ def mstore(evm: Evm) -> None:
     start_position = Uint(pop(evm.stack))
     value = pop(evm.stack).to_be_bytes32()
 
-    total_gas_cost = (
-        calculate_gas_extend_memory(evm.memory, start_position, U256(32))
-        + GAS_VERY_LOW
+    gas_cost_memory_extend = calculate_gas_extend_memory(
+        evm.memory, start_position, U256(32)
+    )
+    total_gas_cost = u256_safe_add(
+        GAS_VERY_LOW,
+        gas_cost_memory_extend,
+        exception_type=OutOfGasError,
     )
     evm.gas_left = subtract_gas(evm.gas_left, total_gas_cost)
 
@@ -83,9 +89,13 @@ def mstore8(evm: Evm) -> None:
     # make sure that value doesn't exceed 1 byte
     normalized_bytes_value = (value & U8_MAX_VALUE).to_be_bytes()
 
-    total_gas_cost = (
-        calculate_gas_extend_memory(evm.memory, start_position, U256(1))
-        + GAS_VERY_LOW
+    memory_extend_gas_cost = calculate_gas_extend_memory(
+        evm.memory, start_position, U256(1)
+    )
+    total_gas_cost = u256_safe_add(
+        GAS_VERY_LOW,
+        memory_extend_gas_cost,
+        exception_type=OutOfGasError,
     )
     evm.gas_left = subtract_gas(evm.gas_left, total_gas_cost)
 
@@ -114,9 +124,13 @@ def mload(evm: Evm) -> None:
     # convert to Uint as start_position + size_to_extend can overflow.
     start_position = Uint(pop(evm.stack))
 
-    total_gas_cost = (
-        calculate_gas_extend_memory(evm.memory, start_position, U256(32))
-        + GAS_VERY_LOW
+    memory_extend_gas_cost = calculate_gas_extend_memory(
+        evm.memory, start_position, U256(32)
+    )
+    total_gas_cost = u256_safe_add(
+        GAS_VERY_LOW,
+        memory_extend_gas_cost,
+        exception_type=OutOfGasError,
     )
     evm.gas_left = subtract_gas(evm.gas_left, total_gas_cost)
 

src/ethereum/frontier/vm/instructions/system.py

@@ -12,6 +12,8 @@
 Implementations of the EVM system related instructions.
 """
 from ethereum.base_types import U256, Uint
+from ethereum.frontier.vm.error import OutOfGasError
+from ethereum.utils.safe_arithmetic import u256_safe_add
 
 from ...state import get_account, increment_nonce, set_account_balance
 from ...utils.address import compute_contract_address, to_address
@@ -45,10 +47,15 @@ def create(evm: Evm) -> None:
     memory_start_position = Uint(pop(evm.stack))
     memory_size = pop(evm.stack)
 
-    gas_cost = GAS_CREATE + calculate_gas_extend_memory(
+    extend_memory_gas_cost = calculate_gas_extend_memory(
         evm.memory, memory_start_position, memory_size
     )
-    evm.gas_left = subtract_gas(evm.gas_left, gas_cost)
+    total_gas_cost = u256_safe_add(
+        GAS_CREATE,
+        extend_memory_gas_cost,
+        exception_type=OutOfGasError,
+    )
+    evm.gas_left = subtract_gas(evm.gas_left, total_gas_cost)
     extend_memory(evm.memory, memory_start_position, memory_size)
     sender_address = evm.env.origin
     sender = get_account(evm.env.state, sender_address)
@@ -141,7 +148,11 @@ def call(evm: Evm) -> None:
     memory_output_size = pop(evm.stack)
 
     call_gas_fee = calculate_call_gas_cost(evm.env.state, gas, to, value)
-    message_call_gas_fee = gas + calculate_message_call_gas_stipend(value)
+    message_call_gas_fee = u256_safe_add(
+        gas,
+        calculate_message_call_gas_stipend(value),
+        exception_type=OutOfGasError,
+    )
 
     evm.gas_left = subtract_gas(evm.gas_left, call_gas_fee)
 
@@ -225,7 +236,11 @@ def callcode(evm: Evm) -> None:
     to = evm.message.current_target
 
     call_gas_fee = calculate_call_gas_cost(evm.env.state, gas, to, value)
-    message_call_gas_fee = gas + calculate_message_call_gas_stipend(value)
+    message_call_gas_fee = u256_safe_add(
+        gas,
+        calculate_message_call_gas_stipend(value),
+        exception_type=OutOfGasError,
+    )
 
     evm.gas_left = subtract_gas(evm.gas_left, call_gas_fee)
 

src/ethereum/frontier/vm/precompiled_contracts/identity.py

@@ -12,7 +12,9 @@
 Implementation of the `IDENTITY` precompiled contract.
 """
 from ethereum.base_types import Uint
+from ethereum.frontier.vm.error import OutOfGasError
 from ethereum.utils.numeric import ceil32
+from ethereum.utils.safe_arithmetic import u256_safe_add, u256_safe_multiply
 
 from ...vm import Evm
 from ...vm.gas import GAS_IDENTITY, GAS_IDENTITY_WORD, subtract_gas
@@ -29,6 +31,15 @@ def identity(evm: Evm) -> None:
     """
     data = evm.message.data
     word_count = ceil32(Uint(len(data))) // 32
-    gas_fee = GAS_IDENTITY + word_count * GAS_IDENTITY_WORD
-    evm.gas_left = subtract_gas(evm.gas_left, gas_fee)
+    word_count_gas_cost = u256_safe_multiply(
+        word_count,
+        GAS_IDENTITY_WORD,
+        exception_type=OutOfGasError,
+    )
+    total_gas_cost = u256_safe_add(
+        GAS_IDENTITY,
+        word_count_gas_cost,
+        exception_type=OutOfGasError,
+    )
+    evm.gas_left = subtract_gas(evm.gas_left, total_gas_cost)
     evm.output = data

src/ethereum/frontier/vm/precompiled_contracts/ripemd160.py

@@ -14,8 +14,10 @@
 import hashlib
 
 from ethereum.base_types import Uint
+from ethereum.frontier.vm.error import OutOfGasError
 from ethereum.utils.byte import left_pad_zero_bytes
 from ethereum.utils.numeric import ceil32
+from ethereum.utils.safe_arithmetic import u256_safe_add, u256_safe_multiply
 
 from ...vm import Evm
 from ...vm.gas import GAS_RIPEMD160, GAS_RIPEMD160_WORD, subtract_gas
@@ -32,8 +34,17 @@ def ripemd160(evm: Evm) -> None:
     """
     data = evm.message.data
     word_count = ceil32(Uint(len(data))) // 32
-    gas_fee = GAS_RIPEMD160 + word_count * GAS_RIPEMD160_WORD
-    evm.gas_left = subtract_gas(evm.gas_left, gas_fee)
+    word_count_gas_cost = u256_safe_multiply(
+        word_count,
+        GAS_RIPEMD160_WORD,
+        exception_type=OutOfGasError,
+    )
+    total_gas_cost = u256_safe_add(
+        GAS_RIPEMD160,
+        word_count_gas_cost,
+        exception_type=OutOfGasError,
+    )
+    evm.gas_left = subtract_gas(evm.gas_left, total_gas_cost)
     hash_bytes = hashlib.new("ripemd160", data).digest()
     padded_hash = left_pad_zero_bytes(hash_bytes, 32)
     evm.output = padded_hash

src/ethereum/frontier/vm/precompiled_contracts/sha256.py

@@ -14,7 +14,9 @@
 import hashlib
 
 from ethereum.base_types import Uint
+from ethereum.frontier.vm.error import OutOfGasError
 from ethereum.utils.numeric import ceil32
+from ethereum.utils.safe_arithmetic import u256_safe_add, u256_safe_multiply
 
 from ...vm import Evm
 from ...vm.gas import GAS_SHA256, GAS_SHA256_WORD, subtract_gas
@@ -31,6 +33,15 @@ def sha256(evm: Evm) -> None:
     """
     data = evm.message.data
     word_count = ceil32(Uint(len(data))) // 32
-    gas_fee = GAS_SHA256 + word_count * GAS_SHA256_WORD
-    evm.gas_left = subtract_gas(evm.gas_left, gas_fee)
+    word_count_gas_cost = u256_safe_multiply(
+        word_count,
+        GAS_SHA256_WORD,
+        exception_type=OutOfGasError,
+    )
+    total_gas_cost = u256_safe_add(
+        GAS_SHA256,
+        word_count_gas_cost,
+        exception_type=OutOfGasError,
+    )
+    evm.gas_left = subtract_gas(evm.gas_left, total_gas_cost)
     evm.output = hashlib.sha256(data).digest()

src/ethereum/utils/safe_arithmetic.py

@@ -11,13 +11,14 @@
 
 Safe arithmetic utility functions for U256 integer type.
 """
-from typing import Optional, Type
+from typing import Optional, Type, Union
 
-from ethereum.base_types import U256
+from ethereum.base_types import U256, Uint
 
 
 def u256_safe_add(
-    *numbers: U256, exception_type: Optional[Type[BaseException]] = None
+    *numbers: Union[U256, Uint],
+    exception_type: Optional[Type[BaseException]] = None
 ) -> U256:
     """
     Adds together the given sequence of numbers. If the total sum of the
@@ -54,7 +55,8 @@ def u256_safe_add(
 
 
 def u256_safe_multiply(
-    *numbers: U256, exception_type: Optional[Type[BaseException]] = None
+    *numbers: Union[U256, Uint],
+    exception_type: Optional[Type[BaseException]] = None
 ) -> U256:
     """
     Multiplies together the given sequence of numbers. If the net product of
@@ -85,7 +87,7 @@ def u256_safe_multiply(
     try:
         for number in numbers[1:]:
             result *= number
-        return result
+        return U256(result)
     except ValueError as e:
         if exception_type:
             raise exception_type from e