Add basic protection aginst circular references in pycdas and pycdc.

This fixes the last case of fuzzer errors detected by #572.

Author: zrax

ASTree.cpp

@@ -1,6 +1,7 @@
 #include <cstring>
 #include <cstdint>
 #include <stdexcept>
+#include <unordered_set>
 #include "ASTree.h"
 #include "FastStack.h"
 #include "pyc_numeric.h"
@@ -2779,6 +2780,8 @@ void print_formatted_value(PycRef<ASTFormattedValue> formatted_value, PycModule*
     pyc_output << "}";
 }
 
+static std::unordered_set<ASTNode *> node_seen;
+
 void print_src(PycRef<ASTNode> node, PycModule* mod, std::ostream& pyc_output)
 {
     if (node == NULL) {
@@ -2787,6 +2790,12 @@ void print_src(PycRef<ASTNode> node, PycModule* mod, std::ostream& pyc_output)
         return;
     }
 
+    if (node_seen.find((ASTNode *)node) != node_seen.end()) {
+        fputs("WARNING: Circular reference detected\n", stderr);
+        return;
+    }
+    node_seen.insert((ASTNode *)node);
+
     switch (node->type()) {
     case ASTNode::NODE_BINARY:
     case ASTNode::NODE_COMPARE:
@@ -3442,10 +3451,12 @@ void print_src(PycRef<ASTNode> node, PycModule* mod, std::ostream& pyc_output)
         pyc_output << "<NODE:" << node->type() << ">";
         fprintf(stderr, "Unsupported Node type: %d\n", node->type());
         cleanBuild = false;
+        node_seen.erase((ASTNode *)node);
         return;
     }
 
     cleanBuild = true;
+    node_seen.erase((ASTNode *)node);
 }
 
 bool print_docstring(PycRef<PycObject> obj, int indent, PycModule* mod,
@@ -3462,8 +3473,16 @@ bool print_docstring(PycRef<PycObject> obj, int indent, PycModule* mod,
     return false;
 }
 
+static std::unordered_set<PycCode *> code_seen;
+
 void decompyle(PycRef<PycCode> code, PycModule* mod, std::ostream& pyc_output)
 {
+    if (code_seen.find((PycCode *)code) != code_seen.end()) {
+        fputs("WARNING: Circular reference detected\n", stderr);
+        return;
+    }
+    code_seen.insert((PycCode *)code);
+
     PycRef<ASTNode> source = BuildFromCode(code, mod);
 
     PycRef<ASTNodeList> clean = source.cast<ASTNodeList>();
@@ -3557,4 +3576,6 @@ void decompyle(PycRef<PycCode> code, PycModule* mod, std::ostream& pyc_output)
         start_line(cur_indent, pyc_output);
         pyc_output << "# WARNING: Decompyle incomplete\n";
     }
+
+    code_seen.erase((PycCode *)code);
 }

pycdas.cpp

@@ -4,6 +4,7 @@
 #include <string>
 #include <iostream>
 #include <fstream>
+#include <unordered_set>
 #include "pyc_module.h"
 #include "pyc_numeric.h"
 #include "bytecode.h"
@@ -73,6 +74,8 @@ static void iprintf(std::ostream& pyc_output, int indent, const char* fmt, ...)
     va_end(varargs);
 }
 
+static std::unordered_set<PycObject *> out_seen;
+
 void output_object(PycRef<PycObject> obj, PycModule* mod, int indent,
                    unsigned flags, std::ostream& pyc_output)
 {
@@ -81,6 +84,12 @@ void output_object(PycRef<PycObject> obj, PycModule* mod, int indent,
         return;
     }
 
+    if (out_seen.find((PycObject *)obj) != out_seen.end()) {
+        fputs("WARNING: Circular reference detected\n", stderr);
+        return;
+    }
+    out_seen.insert((PycObject *)obj);
+
     switch (obj->type()) {
     case PycObject::TYPE_CODE:
     case PycObject::TYPE_CODE2:
@@ -246,6 +255,8 @@ void output_object(PycRef<PycObject> obj, PycModule* mod, int indent,
     default:
         iprintf(pyc_output, indent, "<TYPE: %d>\n", obj->type());
     }
+
+    out_seen.erase((PycObject *)obj);
 }
 
 int main(int argc, char* argv[])