Add and fix JSON stack overflow tests

ccan/json/_info

@@ -27,6 +27,12 @@
  *             "likes_pizza":  true
  *         }
  *     ]
+ * 
+ * The JSON standard supports null characters in strings, due to
+ * difficulties in handling nulls in C strings this is not supported by
+ * this library, json_decode() will return NULL.
+ *
+ * There is also a depth limit of 100 to prevent runaway recursion.
  *
  * Example:
  *	#include <ccan/json/json.h>

ccan/json/json.c

@@ -29,6 +29,8 @@
 #include <stdlib.h>
 #include <string.h>
 
+#define MAX_DEPTH 100
+
 #define out_of_memory() do {                    \
 		fprintf(stderr, "Out of memory.\n");    \
 		exit(EXIT_FAILURE);                     \
@@ -623,6 +625,10 @@ void json_remove_from_parent(JsonNode *node)
 static bool parse_value(const char **sp, JsonNode **out)
 {
 	const char *s = *sp;
+	static int depth = 0;
+
+	if (depth > MAX_DEPTH)
+		return false; // Prevent stack overflow
 
 	switch (*s) {
 		case 'n':
@@ -664,17 +670,23 @@ static bool parse_value(const char **sp, JsonNode **out)
 		}
 
 		case '[':
+			depth++;
 			if (parse_array(&s, out)) {
 				*sp = s;
+				depth--;
 				return true;
 			}
+			depth--;
 			return false;
 
 		case '{':
+			depth++;
 			if (parse_object(&s, out)) {
 				*sp = s;
+				depth--;
 				return true;
 			}
+			depth--;
 			return false;
 
 		default: {

ccan/json/test/run-decode-encode.c

@@ -5,7 +5,7 @@ int main(void)
 	const char *strings_file = "test/test-strings";
 	const char *strings_reencoded_file = "test/test-strings-reencoded";
 	FILE *f, *f2;
-	char buffer[1024], buffer2[1024];
+	char buffer[250010], buffer2[1024];
 
 	plan_tests(90);
 
@@ -24,6 +24,9 @@ int main(void)
 		const char *s = chomp(buffer);
 		bool valid;
 		JsonNode *node;
+
+		diag("HELLO");
+		fprintf(stderr, "#%d %d %s\n", sizeof(buffer), strlen(buffer), buffer);
 
 		if (expect_literal(&s, "valid ")) {
 			valid = true;

ccan/json/test/run-validate.c

@@ -4,9 +4,9 @@ int main(void)
 {
 	const char *strings_file = "test/test-strings";
 	FILE *f;
-	char buffer[1024];
-	
-	plan_tests(224);
+	char buffer[250010];
+
+	plan_tests(226);
 
 	f = fopen(strings_file, "rb");
 	if (f == NULL) {