Check redeemScript size does not exceed 520 byte limit

redeemScripts >520bytes can't be spent due to the
MAX_SCRIPT_ELEMENT_SIZE limit; previously the addmultisigaddress and
createmultisig RPC calls would let you violate that limit unknowingly.

Also made the wallet code itself check the redeemScript prior to adding
it to the wallet, which in the (rare) instance that a user has added an
invalid oversized redeemScript to their wallet causes an error on
startup. The affected key isn't added to the wallet; other keys are
unaffected.

src/keystore.cpp

@@ -33,6 +33,9 @@ bool CBasicKeyStore::AddKeyPubKey(const CKey& key, const CPubKey &pubkey)
 
 bool CBasicKeyStore::AddCScript(const CScript& redeemScript)
 {
+    if (redeemScript.size() > MAX_SCRIPT_ELEMENT_SIZE)
+        return error("CBasicKeyStore::AddCScript() : redeemScripts > %i bytes are invalid", MAX_SCRIPT_ELEMENT_SIZE);
+
     LOCK(cs_KeyStore);
     mapScripts[redeemScript.GetID()] = redeemScript;
     return true;

src/rpcmisc.cpp

@@ -176,7 +176,7 @@ Value validateaddress(const Array& params, bool fHelp)
 //
 // Used by addmultisigaddress / createmultisig:
 //
-CScript _createmultisig(const Array& params)
+CScript _createmultisig_redeemScript(const Array& params)
 {
     int nRequired = params[0].get_int();
     const Array& keys = params[1].get_array();
@@ -228,6 +228,11 @@ CScript _createmultisig(const Array& params)
     }
     CScript result;
     result.SetMultisig(nRequired, pubkeys);
+
+    if (result.size() > MAX_SCRIPT_ELEMENT_SIZE)
+        throw runtime_error(
+                strprintf("redeemScript exceeds size limit: %d > %d", result.size(), MAX_SCRIPT_ELEMENT_SIZE));
+
     return result;
 }
 
@@ -263,7 +268,7 @@ Value createmultisig(const Array& params, bool fHelp)
     }
 
     // Construct using pay-to-script-hash:
-    CScript inner = _createmultisig(params);
+    CScript inner = _createmultisig_redeemScript(params);
     CScriptID innerID = inner.GetID();
     CBitcoinAddress address(innerID);
 

src/rpcwallet.cpp

@@ -871,7 +871,7 @@ Value sendmany(const Array& params, bool fHelp)
 }
 
 // Defined in rpcmisc.cpp
-extern CScript _createmultisig(const Array& params);
+extern CScript _createmultisig_redeemScript(const Array& params);
 
 Value addmultisigaddress(const Array& params, bool fHelp)
 {
@@ -908,7 +908,7 @@ Value addmultisigaddress(const Array& params, bool fHelp)
         strAccount = AccountFromValue(params[2]);
 
     // Construct using pay-to-script-hash:
-    CScript inner = _createmultisig(params);
+    CScript inner = _createmultisig_redeemScript(params);
     CScriptID innerID = inner.GetID();
     pwalletMain->AddCScript(inner);