Merge bitcoin#11284: Fix invalid memory access in CScript::operator+=…

… (guidovranken, ajtowns)

d601f16 Fix invalid memory access in CScript::operator+= (Anthony Towns)

Pull request description:

  This is a fix for bitcoin#11114 -- invoking "s += s" gets turned into "s.insert(s.end(), s.begin(), s.end())" which can result in an invalid memory access is s.capacity() < 2*s.size() (because s gets resized and possibly moved, so s.begin() and s.end() become invalid references when reading the values to be appended).

  The fix is straightforward: reserve enough space in advance, so that insert() doesn't need to resize and thus its arguments remain valid.

  A simple test case is added as well; though you probably need to run it via valgrind to actually catch the problem when it's not fixed...

Tree-SHA512: 4720d0c17463fdc43b344c45fe603423d20b30d48da1b9d85eeedc505d7f34db1ed5495ef1556459ae962a94717e3c6e8fc441763771901efea210d01322b7ef

src/script/script.h

@@ -420,6 +420,7 @@ class CScript : public CScriptBase
 
     CScript& operator+=(const CScript& b)
     {
+        reserve(size() + b.size());
         insert(end(), b.begin(), b.end());
         return *this;
     }

src/test/script_tests.cpp

@@ -1174,4 +1174,21 @@ BOOST_AUTO_TEST_CASE(script_FindAndDelete)
     BOOST_CHECK(s == expect);
 }
 
+BOOST_AUTO_TEST_CASE(script_can_append_self)
+{
+    CScript s, d;
+
+    s = ScriptFromHex("00");
+    s += s;
+    d = ScriptFromHex("0000");
+    BOOST_CHECK(s == d);
+
+    // check doubling a script that's large enough to require reallocation
+    static const char hex[] = "04678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5f";
+    s = CScript() << ParseHex(hex) << OP_CHECKSIG;
+    d = CScript() << ParseHex(hex) << OP_CHECKSIG << ParseHex(hex) << OP_CHECKSIG;
+    s += s;
+    BOOST_CHECK(s == d);
+}
+
 BOOST_AUTO_TEST_SUITE_END()