"""This module contains the detection code for potentially insecure low-level
calls."""
from mythril.analysis import solver
from mythril.analysis.issue_annotation import IssueAnnotation
from mythril.analysis.potential_issues import Issue
from mythril.analysis.swc_data import ASSERT_VIOLATION
from mythril.analysis.module.base import DetectionModule, EntryPoint
from mythril.laser.ethereum.state.global_state import GlobalState
from mythril.laser.smt import Extract, And
from mythril.exceptions import UnsatError
import logging
import eth_abi
log = logging.getLogger(__name__)
DESCRIPTION = """
Search for reachable user-supplied exceptions.
Report a warning if an log message is emitted: 'emit AssertionFailed(string)'
"""
assertion_failed_hash = (
0xB42604CB105A16C8F6DB8A41E6B00C0C1B4826465E8BC504B3EB3E88B3E6A4A0
)
mstore_pattern = "0xcafecafecafecafecafecafecafecafecafecafecafecafecafecafecafe"
[docs]class UserAssertions(DetectionModule):
"""This module searches for user supplied exceptions: emit AssertionFailed("Error")."""
name = "A user-defined assertion has been triggered"
swc_id = ASSERT_VIOLATION
description = DESCRIPTION
entry_point = EntryPoint.CALLBACK
pre_hooks = ["LOG1", "MSTORE"]
def _execute(self, state: GlobalState) -> None:
"""
:param state:
:return:
"""
return self._analyze_state(state)
def _analyze_state(self, state: GlobalState):
"""
:param state:
:return:
"""
opcode = state.get_current_instruction()["opcode"]
message = None
if opcode == "MSTORE":
value = state.mstate.stack[-2]
if value.symbolic:
return []
if mstore_pattern not in hex(value.value)[:126]:
return []
message = "Failed property id {}".format(Extract(15, 0, value).value)
else:
topic, size, mem_start = state.mstate.stack[-3:]
if topic.symbolic or topic.value != assertion_failed_hash:
return []
if not mem_start.symbolic and not size.symbolic:
try:
message = eth_abi.decode_single(
"string",
bytes(
state.mstate.memory[
mem_start.value + 32 : mem_start.value + size.value
]
),
).decode("utf8")
except:
pass
try:
transaction_sequence = solver.get_transaction_sequence(
state, state.world_state.constraints
)
if message:
description_tail = (
"A user-provided assertion failed with the message '{}'".format(
message
)
)
else:
description_tail = "A user-provided assertion failed."
log.debug("MythX assertion emitted: {}".format(description_tail))
address = state.get_current_instruction()["address"]
issue = Issue(
contract=state.environment.active_account.contract_name,
function_name=state.environment.active_function_name,
address=address,
swc_id=ASSERT_VIOLATION,
title="Exception State",
severity="Medium",
description_head="A user-provided assertion failed.",
description_tail=description_tail,
bytecode=state.environment.code.bytecode,
transaction_sequence=transaction_sequence,
gas_used=(state.mstate.min_gas_used, state.mstate.max_gas_used),
)
state.annotate(
IssueAnnotation(
detector=self,
issue=issue,
conditions=[And(*state.world_state.constraints)],
)
)
return [issue]
except UnsatError:
log.debug("no model found")
return []
detector = UserAssertions()