Fix for issue #282

The fix limits recursion depths when parsing arrays and objects.
The limit is configurable via the `JSON_PARSER_MAX_DEPTH` setting
within `jansson_config.h` and is set by default to 2048.

Update the RFC conformance document to note the limit; the RFC
allows limits to be set by the implementation so nothing has
actually changed w.r.t. conformance state.

Reported by Gustavo Grieco.

android/jansson_config.h

@@ -36,4 +36,8 @@
    otherwise to 0. */
 #define JSON_HAVE_LOCALECONV 0
 
+/* Maximum recursion depth for parsing JSON input.
+   This limits the depth of e.g. array-within-array constructions. */
+#define JSON_PARSER_MAX_DEPTH 2048
+
 #endif

cmake/jansson_config.h.cmake

@@ -60,5 +60,9 @@
 #define JSON_HAVE_LOCALECONV @JSON_HAVE_LOCALECONV@
 
 
+/* Maximum recursion depth for parsing JSON input.
+   This limits the depth of e.g. array-within-array constructions. */
+#define JSON_PARSER_MAX_DEPTH 2048
+
 
 #endif

doc/conformance.rst

@@ -108,3 +108,13 @@ types, ``long double``, etc. Obviously, shorter types like ``short``,
 are implicitly handled via the ordinary C type coercion rules (subject
 to overflow semantics). Also, no support or hooks are provided for any
 supplemental "bignum" type add-on packages.
+
+Depth of nested values
+----------------------
+
+To avoid stack exhaustion, Jansson currently limits the nesting depth
+for arrays and objects to a certain value (default: 2048), defined as
+a macro ``JSON_PARSER_MAX_DEPTH`` within ``jansson_config.h``.
+
+The limit is allowed to be set by the RFC; there is no recommended value
+or required minimum depth to be supported.

src/jansson_config.h.in

@@ -36,4 +36,8 @@
    otherwise to 0. */
 #define JSON_HAVE_LOCALECONV @json_have_localeconv@
 
+/* Maximum recursion depth for parsing JSON input.
+   This limits the depth of e.g. array-within-array constructions. */
+#define JSON_PARSER_MAX_DEPTH 2048
+
 #endif

src/load.c

@@ -62,6 +62,7 @@ typedef struct {
     stream_t stream;
     strbuffer_t saved_text;
     size_t flags;
+    size_t depth;
     int token;
     union {
         struct {
@@ -803,6 +804,12 @@ static json_t *parse_value(lex_t *lex, size_t flags, json_error_t *error)
 {
     json_t *json;
 
+    lex->depth++;
+    if(lex->depth > JSON_PARSER_MAX_DEPTH) {
+        error_set(error, lex, "maximum parsing depth reached");
+        return NULL;
+    }
+
     switch(lex->token) {
         case TOKEN_STRING: {
             const char *value = lex->value.string.val;
@@ -865,6 +872,7 @@ static json_t *parse_value(lex_t *lex, size_t flags, json_error_t *error)
     if(!json)
         return NULL;
 
+    lex->depth--;
     return json;
 }
 
@@ -872,6 +880,8 @@ static json_t *parse_json(lex_t *lex, size_t flags, json_error_t *error)
 {
     json_t *result;
 
+    lex->depth = 0;
+
     lex_scan(lex, error);
     if(!(flags & JSON_DECODE_ANY)) {
         if(lex->token != '[' && lex->token != '{') {

test/suites/invalid/recursion-depth/error

@@ -0,0 +1,2 @@
+1 2049 2049
+maximum parsing depth reached near '['