expressions: Parse multiple sets of parentheses for grouping together.

[pspp] / src / language / expressions / parse.c

diff --git a/src/language/expressions/parse.c b/src/language/expressions/parse.c
index 57307bf306f89d6ec83d5f57f33d2a405da71a30..0493ed878bfd98283451eed17b06a66ea88b3409 100644 (file)
--- a/src/language/expressions/parse.c
+++ b/src/language/expressions/parse.c
@@ -953,11 +953,22 @@ parse_primary (struct lexer *lexer, struct expression *e)
 
     case T_LPAREN:
       {
-        union any_node *node;
-       lex_get (lexer);
-       node = parse_or (lexer, e);
-       if (node != NULL && !lex_force_match (lexer, T_RPAREN))
+        /* Count number of left parentheses so that we can match them against
+           an equal number of right parentheses.  This defeats trivial attempts
+           to exhaust the stack with a lot of left parentheses.  (More
+           sophisticated attacks will still succeed.) */
+        size_t n = 0;
+        while (lex_match (lexer, T_LPAREN))
+          n++;
+
+        union any_node *node = parse_or (lexer, e);
+       if (!node)
           return NULL;
+
+        for (size_t i = 0; i < n; i++)
+          if (!lex_force_match (lexer, T_RPAREN))
+            return NULL;
+
         return node;
       }