Implement nesting guard to avoid "out of stack space"

src/ast_def_macros.hpp

@@ -29,6 +29,11 @@ class LocalOption {
 };
 
 #define LOCAL_FLAG(name,opt) LocalOption<bool> flag_##name(name, opt)
+#define LOCAL_COUNT(name,opt) LocalOption<size_t> cnt_##name(name, opt)
+
+#define NESTING_GUARD(name) \
+  LocalOption<size_t> cnt_##name(name, name + 1); \
+  if (nestings > MAX_NESTING) throw Exception::NestingLimitError(pstate); \
 
 #define ATTACH_OPERATIONS()\
 virtual void perform(Operation<void>* op) { (*op)(this); }\

src/error_handling.cpp

@@ -59,6 +59,10 @@ namespace Sass {
     : Base(pstate, msg, import_stack)
     { }
 
+    NestingLimitError::NestingLimitError(ParserState pstate, std::string msg, std::vector<Sass_Import_Entry>* import_stack)
+    : Base(pstate, msg, import_stack)
+    { }
+
     UndefinedOperation::UndefinedOperation(Expression_Ptr_Const lhs, Expression_Ptr_Const rhs, const std::string& op)
     : lhs(lhs), rhs(rhs), op(op)
     {

src/error_handling.hpp

@@ -17,6 +17,7 @@ namespace Sass {
     const std::string def_msg = "Invalid sass detected";
     const std::string def_op_msg = "Undefined operation";
     const std::string def_op_null_msg = "Invalid null operation";
+    const std::string def_nesting_limit = "Code too deeply neested";
 
     class Base : public std::runtime_error {
       protected:
@@ -83,6 +84,12 @@ namespace Sass {
         virtual ~InvalidSyntax() throw() {};
     };
 
+    class NestingLimitError : public Base {
+      public:
+        NestingLimitError(ParserState pstate, std::string msg = def_nesting_limit, std::vector<Sass_Import_Entry>* import_stack = 0);
+        virtual ~NestingLimitError() throw() {};
+    };
+
     /* common virtual base class (has no pstate) */
     class OperationError : public std::runtime_error {
       protected:

src/parser.cpp

@@ -503,6 +503,7 @@ namespace Sass {
   // a ruleset connects a selector and a block
   Ruleset_Obj Parser::parse_ruleset(Lookahead lookahead)
   {
+    NESTING_GUARD(nestings);
     // inherit is_root from parent block
     Block_Obj parent = block_stack.back();
     bool is_root = parent && parent->is_root();
@@ -535,6 +536,7 @@ namespace Sass {
   // in the eval stage we will be re-parse it into an actual selector
   Selector_Schema_Obj Parser::parse_selector_schema(const char* end_of_selector, bool chroot)
   {
+    NESTING_GUARD(nestings);
     // move up to the start
     lex< optional_spaces >();
     const char* i = position;
@@ -646,6 +648,7 @@ namespace Sass {
   {
     bool reloop;
     bool had_linefeed = false;
+    NESTING_GUARD(nestings);
     Complex_Selector_Obj sel;
     Selector_List_Obj group = SASS_MEMORY_NEW(Selector_List, pstate);
     group->media_block(last_media_block);
@@ -700,6 +703,7 @@ namespace Sass {
   Complex_Selector_Obj Parser::parse_complex_selector(bool chroot)
   {
 
+    NESTING_GUARD(nestings);
     String_Obj reference = 0;
     lex < block_comment >();
     advanceToNextToken();
@@ -1055,6 +1059,7 @@ namespace Sass {
 
   Expression_Obj Parser::parse_map()
   {
+    NESTING_GUARD(nestings);
     Expression_Obj key = parse_list();
     List_Obj map = SASS_MEMORY_NEW(List, pstate, 0, SASS_HASH);
 
@@ -1098,6 +1103,7 @@ namespace Sass {
 
   Expression_Obj Parser::parse_bracket_list()
   {
+    NESTING_GUARD(nestings);
     // check if we have an empty list
     // return the empty list as such
     if (peek_css< list_terminator >(position))
@@ -1144,12 +1150,14 @@ namespace Sass {
   // so to speak: we unwrap items from lists if possible here!
   Expression_Obj Parser::parse_list(bool delayed)
   {
+    NESTING_GUARD(nestings);
     return parse_comma_list(delayed);
   }
 
   // will return singletons unwrapped
   Expression_Obj Parser::parse_comma_list(bool delayed)
   {
+    NESTING_GUARD(nestings);
     // check if we have an empty list
     // return the empty list as such
     if (peek_css< list_terminator >(position))
@@ -1189,6 +1197,7 @@ namespace Sass {
   // will return singletons unwrapped
   Expression_Obj Parser::parse_space_list()
   {
+    NESTING_GUARD(nestings);
     Expression_Obj disj1 = parse_disjunction();
     // if it's a singleton, return it (don't wrap it)
     if (peek_css< space_list_terminator >(position)
@@ -1213,6 +1222,7 @@ namespace Sass {
   // parse logical OR operation
   Expression_Obj Parser::parse_disjunction()
   {
+    NESTING_GUARD(nestings);
     advanceToNextToken();
     ParserState state(pstate);
     // parse the left hand side conjunction
@@ -1234,6 +1244,7 @@ namespace Sass {
   // parse logical AND operation
   Expression_Obj Parser::parse_conjunction()
   {
+    NESTING_GUARD(nestings);
     advanceToNextToken();
     ParserState state(pstate);
     // parse the left hand side relation
@@ -1256,6 +1267,7 @@ namespace Sass {
   // parse comparison operations
   Expression_Obj Parser::parse_relation()
   {
+    NESTING_GUARD(nestings);
     advanceToNextToken();
     ParserState state(pstate);
     // parse the left hand side expression
@@ -1308,6 +1320,7 @@ namespace Sass {
   // parse addition and subtraction operations
   Expression_Obj Parser::parse_expression()
   {
+    NESTING_GUARD(nestings);
     advanceToNextToken();
     ParserState state(pstate);
     // parses multiple add and subtract operations
@@ -1351,6 +1364,7 @@ namespace Sass {
   // parse addition and subtraction operations
   Expression_Obj Parser::parse_operators()
   {
+    NESTING_GUARD(nestings);
     advanceToNextToken();
     ParserState state(pstate);
     Expression_Obj factor = parse_factor();
@@ -1383,6 +1397,7 @@ namespace Sass {
   // called from parse_value_schema
   Expression_Obj Parser::parse_factor()
   {
+    NESTING_GUARD(nestings);
     lex < css_comments >(false);
     if (lex_css< exactly<'('> >()) {
       // parse_map may return a list

src/parser.hpp

@@ -10,6 +10,15 @@
 #include "position.hpp"
 #include "prelexer.hpp"
 
+#ifndef MAX_NESTING
+// Note that this limit is not an exact science
+// it depends on various factors, which some are
+// not under our control (compile time or even OS
+// dependent settings on the available stack size)
+// It should fix most common segfault cases though.
+#define MAX_NESTING 512
+#endif
+
 struct Lookahead {
   const char* found;
   const char* error;
@@ -35,13 +44,14 @@ namespace Sass {
     Position before_token;
     Position after_token;
     ParserState pstate;
-    int indentation;
+    size_t indentation;
+    size_t nestings;
 
     Token lexed;
 
     Parser(Context& ctx, const ParserState& pstate)
     : ParserState(pstate), ctx(ctx), block_stack(), stack(0), last_media_block(),
-      source(0), position(0), end(0), before_token(pstate), after_token(pstate), pstate(pstate), indentation(0)
+      source(0), position(0), end(0), before_token(pstate), after_token(pstate), pstate(pstate), indentation(0), nestings(0)
     { stack.push_back(Scope::Root); }
 
     // static Parser from_string(const std::string& src, Context& ctx, ParserState pstate = ParserState("[STRING]"));