Vyper vulnerable to memory corruption in certain builtins utilizing `msize`

Impact

In certain conditions, the memory used by the builtins raw_call, create_from_blueprint and create_copy_of can be corrupted.

• For raw_call, the argument buffer of the call can be corrupted, leading to incorrect calldata in the sub-context.
• For create_from_blueprint and create_copy_of, the buffer for the to-be-deployed bytecode can be corrupted, leading to deploying incorrect bytecode.

Below are the conditions that must be fulfilled for the corruption to happen for each builtin:

raw_call

• memory is not fully initialized, ex. all parameters to an external function live in calldata and
• The data argument of the builtin is msg.data. and
• The to, value or gas passed to the builtin is some complex expression that results in writing to uninitialized memory (e.g. calling an internal function)

create_copy_of

• memory is not fully initialized, ex. all parameters to an external function live in calldata and
• The value or salt passed to the builtin is some complex expression that results in writing to uninitialized memory (e.g. calling an internal function)

create_from_blueprint

• memory is not fully initialized, ex. all parameters to an external function live in calldata and
• Either no constructor parameters are passed to the builtin or raw_args is set to True. and
• The value or salt passed to the builtin is some complex expression that results in writing to uninitialized memory (e.g. calling an internal function)

Note: When the builtin is being called from an internal function f from a function g, the issue is not present provided that g has written to memory before calling f.

Examples

raw_call

In the following contract, calling bar(1,1) will return:

ae42e95100000000000000000000000000000000000000000000000000000000ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff00000001

instead of:

ae42e95100000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000001

identity: constant(address) = 0x0000000000000000000000000000000000000004

@external
def foo():
    pass

@internal
@view
def get_address()->address:
    a:uint256 = max_value(uint256) # 0xfff...fff
    return identity
@external
def bar(f:uint256, u:uint256) -> Bytes[100]:
    a: Bytes[100] = raw_call(self.get_address(), msg.data, max_outsize=100)
    return a

create_copy_of

In the following contract, after calling test(), the code deployed at self.created_address does not match the bytecode at target.

created_address: public(address)

@external
def test(target: address) -> address:
    # The expression in salt= is complex and will require to store to memory
    self.created_address = create_copy_of(target, salt = keccak256(_abi_encode(target)))
    return self.created_address

create_from_blueprint

In the following contract, after calling test(), the init bytecode used to create the contract deployed at the address self.created_address will not match the blueprint bytecode stored at target.

created_address: public(address)

salt: constant(bytes32) = keccak256("kebab")

@external
@payable
def test(target: address):
    # The expression in salt= is complex and will require to store to memory
    self.created_address = create_from_blueprint(target, code_offset=0, salt=keccak256(_abi_encode(target)))

Patches

issue tracking in https://github.com/vyperlang/vyper/issues/3609, patched in #3610

Workarounds

The complex expressions that are being passed as kwargs to the builtin should be cached in memory prior to the call to the builtin. For the last example above, it would be:

created_address: public(address)

salt: constant(bytes32) = keccak256("kebab")

@external
@payable
def test(target: address):
    salt: bytes32 = keccak256(_abi_encode(target))
    self.created_address = create_from_blueprint(target, code_offset=0, salt=salt)

References

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