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-rw-r--r--src/script/interpreter.cpp15
-rw-r--r--src/script/interpreter.h10
-rw-r--r--src/script/script_error.h1
3 files changed, 21 insertions, 5 deletions
diff --git a/src/script/interpreter.cpp b/src/script/interpreter.cpp
index d97f917c37..1b187f5ef5 100644
--- a/src/script/interpreter.cpp
+++ b/src/script/interpreter.cpp
@@ -1096,7 +1096,6 @@ bool VerifyScript(const CScript& scriptSig, const CScript& scriptPubKey, unsigne
return false;
if (stack.empty())
return set_error(serror, SCRIPT_ERR_EVAL_FALSE);
-
if (CastToBool(stack.back()) == false)
return set_error(serror, SCRIPT_ERR_EVAL_FALSE);
@@ -1126,8 +1125,18 @@ bool VerifyScript(const CScript& scriptSig, const CScript& scriptPubKey, unsigne
return set_error(serror, SCRIPT_ERR_EVAL_FALSE);
if (!CastToBool(stack.back()))
return set_error(serror, SCRIPT_ERR_EVAL_FALSE);
- else
- return set_success(serror);
+ }
+
+ // The CLEANSTACK check is only performed after potential P2SH evaluation,
+ // as the non-P2SH evaluation of a P2SH script will obviously not result in
+ // a clean stack (the P2SH inputs remain).
+ if ((flags & SCRIPT_VERIFY_CLEANSTACK) != 0) {
+ // Disallow CLEANSTACK without P2SH, as otherwise a switch CLEANSTACK->P2SH+CLEANSTACK
+ // would be possible, which is not a softfork (and P2SH should be one).
+ assert((flags & SCRIPT_VERIFY_P2SH) != 0);
+ if (stack.size() != 1) {
+ return set_error(serror, SCRIPT_ERR_CLEANSTACK);
+ }
}
return set_success(serror);
diff --git a/src/script/interpreter.h b/src/script/interpreter.h
index 35b2f6c65a..9b35b176ae 100644
--- a/src/script/interpreter.h
+++ b/src/script/interpreter.h
@@ -67,8 +67,14 @@ enum
// discouraged NOPs fails the script. This verification flag will never be
// a mandatory flag applied to scripts in a block. NOPs that are not
// executed, e.g. within an unexecuted IF ENDIF block, are *not* rejected.
- SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_NOPS = (1U << 7)
-
+ SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_NOPS = (1U << 7),
+
+ // Require that only a single stack element remains after evaluation. This changes the success criterion from
+ // "At least one stack element must remain, and when interpreted as a boolean, it must be true" to
+ // "Exactly one stack element must remain, and when interpreted as a boolean, it must be true".
+ // (softfork safe, BIP62 rule 6)
+ // Note: CLEANSTACK should never be used without P2SH.
+ SCRIPT_VERIFY_CLEANSTACK = (1U << 8),
};
uint256 SignatureHash(const CScript &scriptCode, const CTransaction& txTo, unsigned int nIn, int nHashType);
diff --git a/src/script/script_error.h b/src/script/script_error.h
index ac1f2deae5..f085b63032 100644
--- a/src/script/script_error.h
+++ b/src/script/script_error.h
@@ -43,6 +43,7 @@ typedef enum ScriptError_t
SCRIPT_ERR_SIG_HIGH_S,
SCRIPT_ERR_SIG_NULLDUMMY,
SCRIPT_ERR_PUBKEYTYPE,
+ SCRIPT_ERR_CLEANSTACK,
/* softfork safeness */
SCRIPT_ERR_DISCOURAGE_UPGRADABLE_NOPS,