added online lookup for signature hashes via 4bytes.directory

mythril/disassembler/disassembly.py

@@ -1,6 +1,5 @@
 from mythril.ether import asm,util
-import os
-import json
+from mythril.support.signatures import Signatures
 import logging
 
 
@@ -13,21 +12,11 @@ class Disassembly:
         self.addr_to_func = {}
         self.bytecode = code
 
+        signatures = Signatures(enable_online_lookkup=True)  # control if you want to have online sighash lookups
         try:
-            mythril_dir = os.environ['MYTHRIL_DIR']
-        except KeyError:
-            mythril_dir = os.path.join(os.path.expanduser('~'), ".mythril")
-
-        # Load function signatures
-
-        signatures_file = os.path.join(mythril_dir, 'signatures.json')
-
-        if not os.path.exists(signatures_file):
-            logging.info("Missing function signature file. Resolving of function names disabled.")
-            signatures = {}
-        else:
-            with open(signatures_file) as f:
-                signatures = json.load(f)
+            signatures.open()  # open from default locations
+        except FileNotFoundError:
+            logging.info("Missing function signature file. Resolving of function names from disabled.")
 
         # Parse jump table & resolve function names
 
@@ -36,7 +25,7 @@ class Disassembly:
         for i in jmptable_indices:
             func_hash = self.instruction_list[i]['argument']
             try:
-                func_name = signatures[func_hash]
+                func_name = signatures.get(func_hash)  # tries local cache, file and optional online lookup
             except KeyError:
                 func_name = "_function_" + func_hash
 
@@ -49,8 +38,5 @@ class Disassembly:
             except:
                 continue
 
-
-
     def get_easm(self):
-
         return asm.instruction_list_to_easm(self.instruction_list)

mythril/support/signatures.py

@@ -1,7 +1,17 @@
 import re
+import os
+import logging
+import json
 from ethereum import utils
 
+try:
+    # load if available but do not fail
+    import ethereum_input_decoder
+except ImportError:
+    ethereum_input_decoder = None
 
+
+# TODO: tintinweb: move this and signature functionality from mythril.py to class Signatures to have one single interface.
 def add_signatures_from_file(file, sigs={}):
 
     funcs = []
@@ -42,3 +52,60 @@ def add_signatures_from_file(file, sigs={}):
             signature = re.sub(r'\s', '', signature)
 
             sigs["0x" + utils.sha3(signature)[:4].hex()] = signature
+
+
+class Signatures(object):
+
+    def __init__(self, enable_online_lookkup=True):
+        self.signatures = {}  # signatures in-mem cache
+        self.enable_online_lookup =enable_online_lookkup  # enable online funcsig resolving
+
+    def open(self, path=None):
+        if not path:
+            #  try default locations
+            try:
+                mythril_dir = os.environ['MYTHRIL_DIR']
+            except KeyError:
+                mythril_dir = os.path.join(os.path.expanduser('~'), ".mythril")
+            path = os.path.join(mythril_dir, 'signatures.json')
+
+        if not os.path.exists(path):
+            raise FileNotFoundError("Missing function signature file. Resolving of function names disabled.")
+
+        with open(path) as f:
+            sigs = json.load(f)
+
+        # normalize it to {sighash:list(signatures,...)}
+        for sighash,funcsig in sigs.items():
+            self.signatures.setdefault(sighash, [])
+            self.signatures[sighash].append(funcsig)
+
+        return self
+
+    def get(self, sighash):
+        """
+        get a function signature for a sighash
+        1) try local cache
+        2) try online lookup
+        :param sighash:
+        :return: list of function signatures
+        """
+        if not self.signatures.get(sighash) and self.enable_online_lookup:
+            self.signatures[sighash] = Signatures.lookup_online(sighash)  # might return multiple sigs
+        return self.signatures.get(sighash)
+
+
+    @staticmethod
+    def lookup_online(sighash):
+        """
+        Lookup function signatures from 4bytes.directory.
+        //tintinweb: the smart-contract-sanctuary project dumps contracts from etherscan.io and feeds them into
+                     4bytes.directory.
+                     https://github.com/tintinweb/smart-contract-sanctuary
+
+        :param s: function signature as hexstr
+        :return: a list of possible function signatures for this hash
+        """
+        if not ethereum_input_decoder:
+            return None
+        return list(ethereum_input_decoder.decoder.FourByteDirectory.lookup_signatures(sighash))