Add rejection of non-null CHECKMULTISIG dummy values

This is a source of transaction mutability as the dummy value was
previously not checked and could be modified to something other than the
usual OP_0 value.

src/script.cpp

@@ -934,8 +934,22 @@ bool EvalScript(vector<vector<unsigned char> >& stack, const CScript& script, co
                             fSuccess = false;
                     }
 
-                    while (i-- > 0)
+                    // Clean up stack of actual arguments
+                    while (i-- > 1)
                         popstack(stack);
+
+                    // A bug causes CHECKMULTISIG to consume one extra argument
+                    // whose contents were not checked in any way.
+                    //
+                    // Unfortunately this is a potential source of mutability,
+                    // so optionally verify it is exactly equal to zero prior
+                    // to removing it from the stack.
+                    if (stack.size() < 1)
+                        return false;
+                    if ((flags & SCRIPT_VERIFY_NULLDUMMY) && stacktop(-1).size())
+                        return error("CHECKMULTISIG dummy argument not null");
+                    popstack(stack);
+
                     stack.push_back(fSuccess ? vchTrue : vchFalse);
 
                     if (opcode == OP_CHECKMULTISIGVERIFY)

src/script.h

@@ -42,6 +42,7 @@ enum
     SCRIPT_VERIFY_STRICTENC = (1U << 1), // enforce strict conformance to DER and SEC2 for signatures and pubkeys
     SCRIPT_VERIFY_EVEN_S    = (1U << 2), // enforce even S values in signatures (depends on STRICTENC)
     SCRIPT_VERIFY_NOCACHE   = (1U << 3), // do not store results in signature cache (but do query it)
+    SCRIPT_VERIFY_NULLDUMMY = (1U << 4), // verify dummy stack item consumed by CHECKMULTISIG is of zero-length
 };
 
 // Mandatory script verification flags that all new blocks must comply with for
@@ -54,7 +55,8 @@ static const unsigned int MANDATORY_SCRIPT_VERIFY_FLAGS = SCRIPT_VERIFY_P2SH;
 // with. However scripts violating these flags may still be present in valid
 // blocks and we must accept those blocks.
 static const unsigned int STANDARD_SCRIPT_VERIFY_FLAGS = MANDATORY_SCRIPT_VERIFY_FLAGS |
-                                                         SCRIPT_VERIFY_STRICTENC;
+                                                         SCRIPT_VERIFY_STRICTENC |
+                                                         SCRIPT_VERIFY_NULLDUMMY;
 
 enum txnouttype
 {

src/test/data/tx_invalid.json

@@ -67,11 +67,38 @@
   ["0000000000000000000000000000000000000000000000000000000000000200", 0, "0x21 0x035e7f0d4d0841bcd56c39337ed086b1a633ee770c1ffdd94ac552a95ac2ce0efc CHECKSIG"]],
  "01000000020001000000000000000000000000000000000000000000000000000000000000000000004948304502203a0f5f0e1f2bdbcd04db3061d18f3af70e07f4f467cbc1b8116f267025f5360b022100c792b6e215afc5afc721a351ec413e714305cb749aae3d7fee76621313418df10101000000000200000000000000000000000000000000000000000000000000000000000000000000484730440220201dc2d030e380e8f9cfb41b442d930fa5a685bb2c8db5906671f865507d0670022018d9e7a8d4c8d86a73c2a724ee38ef983ec249827e0e464841735955c707ece98101000000010100000000000000015100000000", "P2SH"],
 
-["Incorrect signature order"],
+["CHECKMULTISIG with incorrect signature order"],
 ["Note the input is just required to make the tester happy"],
 [[["b3da01dd4aae683c7aee4d5d8b52a540a508e1115f77cd7fa9a291243f501223", 0, "HASH160 0x14 0xb1ce99298d5f07364b57b1e5c9cc00be0b04a954 EQUAL"]],
 "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", "P2SH"],
 
+
+["The following is a tweaked form of 23b397edccd3740a74adb603c9756370fafcde9bcc4483eb271ecad09a94dd63"],
+["It is an OP_CHECKMULTISIG with the dummy value missing"],
+[[["60a20bd93aa49ab4b28d514ec10b06e1829ce6818ec06cd3aabd013ebcdc4bb1", 0, "1 0x41 0x04cc71eb30d653c0c3163990c47b976f3fb3f37cccdcbedb169a1dfef58bbfbfaff7d8a473e7e2e6d317b87bafe8bde97e3cf8f065dec022b51d11fcdd0d348ac4 0x41 0x0461cbdcc5409fb4b4d42b51d33381354d80e550078cb532a34bfa2fcfdeb7d76519aecc62770f5b0e4ef8551946d8a540911abe3e7854a26f39f58b25c15342af 2 OP_CHECKMULTISIG"]],
+"0100000001b14bdcbc3e01bdaad36cc08e81e69c82e1060bc14e518db2b49aa43ad90ba260000000004847304402203f16c6f40162ab686621ef3000b04e75418a0c0cb2d8aebeac894ae360ac1e780220ddc15ecdfc3507ac48e1681a33eb60996631bf6bf5bc0a0682c4db743ce7ca2b01ffffffff0140420f00000000001976a914660d4ef3a743e3e696ad990364e555c271ad504b88ac00000000", "P2SH"],
+
+
+["CHECKMULTISIG SCRIPT_VERIFY_NULLDUMMY tests:"],
+
+["The following is a tweaked form of 23b397edccd3740a74adb603c9756370fafcde9bcc4483eb271ecad09a94dd63"],
+["It is an OP_CHECKMULTISIG with the dummy value set to something other than an empty string"],
+[[["60a20bd93aa49ab4b28d514ec10b06e1829ce6818ec06cd3aabd013ebcdc4bb1", 0, "1 0x41 0x04cc71eb30d653c0c3163990c47b976f3fb3f37cccdcbedb169a1dfef58bbfbfaff7d8a473e7e2e6d317b87bafe8bde97e3cf8f065dec022b51d11fcdd0d348ac4 0x41 0x0461cbdcc5409fb4b4d42b51d33381354d80e550078cb532a34bfa2fcfdeb7d76519aecc62770f5b0e4ef8551946d8a540911abe3e7854a26f39f58b25c15342af 2 OP_CHECKMULTISIG"]],
+"0100000001b14bdcbc3e01bdaad36cc08e81e69c82e1060bc14e518db2b49aa43ad90ba260000000004a010047304402203f16c6f40162ab686621ef3000b04e75418a0c0cb2d8aebeac894ae360ac1e780220ddc15ecdfc3507ac48e1681a33eb60996631bf6bf5bc0a0682c4db743ce7ca2b01ffffffff0140420f00000000001976a914660d4ef3a743e3e696ad990364e555c271ad504b88ac00000000", "P2SH,NULLDUMMY"],
+
+["As above, but using a OP_1"],
+[[["60a20bd93aa49ab4b28d514ec10b06e1829ce6818ec06cd3aabd013ebcdc4bb1", 0, "1 0x41 0x04cc71eb30d653c0c3163990c47b976f3fb3f37cccdcbedb169a1dfef58bbfbfaff7d8a473e7e2e6d317b87bafe8bde97e3cf8f065dec022b51d11fcdd0d348ac4 0x41 0x0461cbdcc5409fb4b4d42b51d33381354d80e550078cb532a34bfa2fcfdeb7d76519aecc62770f5b0e4ef8551946d8a540911abe3e7854a26f39f58b25c15342af 2 OP_CHECKMULTISIG"]],
+"0100000001b14bdcbc3e01bdaad36cc08e81e69c82e1060bc14e518db2b49aa43ad90ba26000000000495147304402203f16c6f40162ab686621ef3000b04e75418a0c0cb2d8aebeac894ae360ac1e780220ddc15ecdfc3507ac48e1681a33eb60996631bf6bf5bc0a0682c4db743ce7ca2b01ffffffff0140420f00000000001976a914660d4ef3a743e3e696ad990364e555c271ad504b88ac00000000", "P2SH,NULLDUMMY"],
+
+["As above, but using a OP_1NEGATE"],
+[[["60a20bd93aa49ab4b28d514ec10b06e1829ce6818ec06cd3aabd013ebcdc4bb1", 0, "1 0x41 0x04cc71eb30d653c0c3163990c47b976f3fb3f37cccdcbedb169a1dfef58bbfbfaff7d8a473e7e2e6d317b87bafe8bde97e3cf8f065dec022b51d11fcdd0d348ac4 0x41 0x0461cbdcc5409fb4b4d42b51d33381354d80e550078cb532a34bfa2fcfdeb7d76519aecc62770f5b0e4ef8551946d8a540911abe3e7854a26f39f58b25c15342af 2 OP_CHECKMULTISIG"]],
+"0100000001b14bdcbc3e01bdaad36cc08e81e69c82e1060bc14e518db2b49aa43ad90ba26000000000494f47304402203f16c6f40162ab686621ef3000b04e75418a0c0cb2d8aebeac894ae360ac1e780220ddc15ecdfc3507ac48e1681a33eb60996631bf6bf5bc0a0682c4db743ce7ca2b01ffffffff0140420f00000000001976a914660d4ef3a743e3e696ad990364e555c271ad504b88ac00000000", "P2SH,NULLDUMMY"],
+
+["As above, but with the dummy byte missing"],
+[[["60a20bd93aa49ab4b28d514ec10b06e1829ce6818ec06cd3aabd013ebcdc4bb1", 0, "1 0x41 0x04cc71eb30d653c0c3163990c47b976f3fb3f37cccdcbedb169a1dfef58bbfbfaff7d8a473e7e2e6d317b87bafe8bde97e3cf8f065dec022b51d11fcdd0d348ac4 0x41 0x0461cbdcc5409fb4b4d42b51d33381354d80e550078cb532a34bfa2fcfdeb7d76519aecc62770f5b0e4ef8551946d8a540911abe3e7854a26f39f58b25c15342af 2 OP_CHECKMULTISIG"]],
+"0100000001b14bdcbc3e01bdaad36cc08e81e69c82e1060bc14e518db2b49aa43ad90ba260000000004847304402203f16c6f40162ab686621ef3000b04e75418a0c0cb2d8aebeac894ae360ac1e780220ddc15ecdfc3507ac48e1681a33eb60996631bf6bf5bc0a0682c4db743ce7ca2b01ffffffff0140420f00000000001976a914660d4ef3a743e3e696ad990364e555c271ad504b88ac00000000", "P2SH,NULLDUMMY"],
+
+
 ["Empty stack when we try to run CHECKSIG"],
 [[["ad503f72c18df5801ee64d76090afe4c607fb2b822e9b7b63c5826c50e22fc3b", 0, "0x21 0x027c3a97665bf283a102a587a62a30a0c102d4d3b141015e2cae6f64e2543113e5 CHECKSIG NOT"]],
 "01000000013bfc220ec526583cb6b7e922b8b27f604cfe0a09764de61e80f58dc1723f50ad0000000000ffffffff0101000000000000002321027c3a97665bf283a102a587a62a30a0c102d4d3b141015e2cae6f64e2543113e5ac00000000", "P2SH"],

src/test/data/tx_valid.json

@@ -13,9 +13,23 @@
 "0100000001b14bdcbc3e01bdaad36cc08e81e69c82e1060bc14e518db2b49aa43ad90ba26000000000490047304402203f16c6f40162ab686621ef3000b04e75418a0c0cb2d8aebeac894ae360ac1e780220ddc15ecdfc3507ac48e1681a33eb60996631bf6bf5bc0a0682c4db743ce7ca2b01ffffffff0140420f00000000001976a914660d4ef3a743e3e696ad990364e555c271ad504b88ac00000000", "P2SH"],
 
 ["The following is a tweaked form of 23b397edccd3740a74adb603c9756370fafcde9bcc4483eb271ecad09a94dd63"],
-["It has an arbitrary extra byte stuffed into the signature at pos length - 2"],
+["It is an OP_CHECKMULTISIG with an arbitrary extra byte stuffed into the signature at pos length - 2"],
+["The dummy byte is fine however, so the NULLDUMMY flag should be happy"],
 [[["60a20bd93aa49ab4b28d514ec10b06e1829ce6818ec06cd3aabd013ebcdc4bb1", 0, "1 0x41 0x04cc71eb30d653c0c3163990c47b976f3fb3f37cccdcbedb169a1dfef58bbfbfaff7d8a473e7e2e6d317b87bafe8bde97e3cf8f065dec022b51d11fcdd0d348ac4 0x41 0x0461cbdcc5409fb4b4d42b51d33381354d80e550078cb532a34bfa2fcfdeb7d76519aecc62770f5b0e4ef8551946d8a540911abe3e7854a26f39f58b25c15342af 2 OP_CHECKMULTISIG"]],
-"0100000001b14bdcbc3e01bdaad36cc08e81e69c82e1060bc14e518db2b49aa43ad90ba260000000004A0048304402203f16c6f40162ab686621ef3000b04e75418a0c0cb2d8aebeac894ae360ac1e780220ddc15ecdfc3507ac48e1681a33eb60996631bf6bf5bc0a0682c4db743ce7ca2bab01ffffffff0140420f00000000001976a914660d4ef3a743e3e696ad990364e555c271ad504b88ac00000000", "P2SH"],
+"0100000001b14bdcbc3e01bdaad36cc08e81e69c82e1060bc14e518db2b49aa43ad90ba260000000004A0048304402203f16c6f40162ab686621ef3000b04e75418a0c0cb2d8aebeac894ae360ac1e780220ddc15ecdfc3507ac48e1681a33eb60996631bf6bf5bc0a0682c4db743ce7ca2bab01ffffffff0140420f00000000001976a914660d4ef3a743e3e696ad990364e555c271ad504b88ac00000000", "P2SH,NULLDUMMY"],
+
+["The following is a tweaked form of 23b397edccd3740a74adb603c9756370fafcde9bcc4483eb271ecad09a94dd63"],
+["It is an OP_CHECKMULTISIG with the dummy value set to something other than an empty string"],
+[[["60a20bd93aa49ab4b28d514ec10b06e1829ce6818ec06cd3aabd013ebcdc4bb1", 0, "1 0x41 0x04cc71eb30d653c0c3163990c47b976f3fb3f37cccdcbedb169a1dfef58bbfbfaff7d8a473e7e2e6d317b87bafe8bde97e3cf8f065dec022b51d11fcdd0d348ac4 0x41 0x0461cbdcc5409fb4b4d42b51d33381354d80e550078cb532a34bfa2fcfdeb7d76519aecc62770f5b0e4ef8551946d8a540911abe3e7854a26f39f58b25c15342af 2 OP_CHECKMULTISIG"]],
+"0100000001b14bdcbc3e01bdaad36cc08e81e69c82e1060bc14e518db2b49aa43ad90ba260000000004a01ff47304402203f16c6f40162ab686621ef3000b04e75418a0c0cb2d8aebeac894ae360ac1e780220ddc15ecdfc3507ac48e1681a33eb60996631bf6bf5bc0a0682c4db743ce7ca2b01ffffffff0140420f00000000001976a914660d4ef3a743e3e696ad990364e555c271ad504b88ac00000000", "P2SH"],
+
+["As above, but using a OP_1"],
+[[["60a20bd93aa49ab4b28d514ec10b06e1829ce6818ec06cd3aabd013ebcdc4bb1", 0, "1 0x41 0x04cc71eb30d653c0c3163990c47b976f3fb3f37cccdcbedb169a1dfef58bbfbfaff7d8a473e7e2e6d317b87bafe8bde97e3cf8f065dec022b51d11fcdd0d348ac4 0x41 0x0461cbdcc5409fb4b4d42b51d33381354d80e550078cb532a34bfa2fcfdeb7d76519aecc62770f5b0e4ef8551946d8a540911abe3e7854a26f39f58b25c15342af 2 OP_CHECKMULTISIG"]],
+"0100000001b14bdcbc3e01bdaad36cc08e81e69c82e1060bc14e518db2b49aa43ad90ba26000000000495147304402203f16c6f40162ab686621ef3000b04e75418a0c0cb2d8aebeac894ae360ac1e780220ddc15ecdfc3507ac48e1681a33eb60996631bf6bf5bc0a0682c4db743ce7ca2b01ffffffff0140420f00000000001976a914660d4ef3a743e3e696ad990364e555c271ad504b88ac00000000", "P2SH"],
+
+["As above, but using a OP_1NEGATE"],
+[[["60a20bd93aa49ab4b28d514ec10b06e1829ce6818ec06cd3aabd013ebcdc4bb1", 0, "1 0x41 0x04cc71eb30d653c0c3163990c47b976f3fb3f37cccdcbedb169a1dfef58bbfbfaff7d8a473e7e2e6d317b87bafe8bde97e3cf8f065dec022b51d11fcdd0d348ac4 0x41 0x0461cbdcc5409fb4b4d42b51d33381354d80e550078cb532a34bfa2fcfdeb7d76519aecc62770f5b0e4ef8551946d8a540911abe3e7854a26f39f58b25c15342af 2 OP_CHECKMULTISIG"]],
+"0100000001b14bdcbc3e01bdaad36cc08e81e69c82e1060bc14e518db2b49aa43ad90ba26000000000494f47304402203f16c6f40162ab686621ef3000b04e75418a0c0cb2d8aebeac894ae360ac1e780220ddc15ecdfc3507ac48e1681a33eb60996631bf6bf5bc0a0682c4db743ce7ca2b01ffffffff0140420f00000000001976a914660d4ef3a743e3e696ad990364e555c271ad504b88ac00000000", "P2SH"],
 
 ["The following is c99c49da4c38af669dea436d3e73780dfdb6c1ecf9958baa52960e8baee30e73"],
 ["It is of interest because it contains a 0-sequence as well as a signature of SIGHASH type 0 (which is not a real type)"],

src/test/transaction_tests.cpp

@@ -39,6 +39,7 @@ unsigned int ParseFlags(string strFlags){
         mapFlagNames["P2SH"] = SCRIPT_VERIFY_P2SH;
         mapFlagNames["STRICTENC"] = SCRIPT_VERIFY_STRICTENC;
         mapFlagNames["EVEN_S"] = SCRIPT_VERIFY_EVEN_S;
+        mapFlagNames["NULLDUMMY"] = SCRIPT_VERIFY_NULLDUMMY;
     }
 
     BOOST_FOREACH(string word, words)