Support configurable limit on depth of JSON parsing

apache2/apache2_config.c

@@ -50,6 +50,7 @@ void *create_directory_config(apr_pool_t *mp, char *path)
     dcfg->reqbody_inmemory_limit = NOT_SET;
     dcfg->reqbody_limit = NOT_SET;
     dcfg->reqbody_no_files_limit = NOT_SET;
+    dcfg->reqbody_json_depth_limit = NOT_SET;
     dcfg->resbody_access = NOT_SET;
 
     dcfg->debuglog_name = NOT_SET_P;
@@ -332,6 +333,8 @@ void *merge_directory_configs(apr_pool_t *mp, void *_parent, void *_child)
         ? parent->reqbody_limit : child->reqbody_limit);
     merged->reqbody_no_files_limit = (child->reqbody_no_files_limit == NOT_SET
         ? parent->reqbody_no_files_limit : child->reqbody_no_files_limit);
+    merged->reqbody_json_depth_limit = (child->reqbody_json_depth_limit == NOT_SET
+        ? parent->reqbody_json_depth_limit : child->reqbody_json_depth_limit);
     merged->resbody_access = (child->resbody_access == NOT_SET
         ? parent->resbody_access : child->resbody_access);
 
@@ -648,6 +651,7 @@ void init_directory_config(directory_config *dcfg)
         dcfg->reqbody_inmemory_limit = REQUEST_BODY_DEFAULT_INMEMORY_LIMIT;
     if (dcfg->reqbody_limit == NOT_SET) dcfg->reqbody_limit = REQUEST_BODY_DEFAULT_LIMIT;
     if (dcfg->reqbody_no_files_limit == NOT_SET) dcfg->reqbody_no_files_limit = REQUEST_BODY_NO_FILES_DEFAULT_LIMIT;
+    if (dcfg->reqbody_json_depth_limit == NOT_SET) dcfg->reqbody_json_depth_limit = REQUEST_BODY_JSON_DEPTH_DEFAULT_LIMIT;
     if (dcfg->resbody_access == NOT_SET) dcfg->resbody_access = 0;
     if (dcfg->of_limit == NOT_SET) dcfg->of_limit = RESPONSE_BODY_DEFAULT_LIMIT;
     if (dcfg->if_limit_action == NOT_SET) dcfg->if_limit_action = REQUEST_BODY_LIMIT_ACTION_REJECT;
@@ -1920,6 +1924,24 @@ static const char *cmd_request_body_no_files_limit(cmd_parms *cmd, void *_dcfg,
     return NULL;
 }
 
+static const char *cmd_request_body_json_depth_limit(cmd_parms *cmd, void *_dcfg,
+                                                     const char *p1)
+{
+    directory_config *dcfg = (directory_config *)_dcfg;
+    long int limit;
+
+    if (dcfg == NULL) return NULL;
+
+    limit = strtol(p1, NULL, 10);
+    if ((limit == LONG_MAX)||(limit == LONG_MIN)||(limit <= 0)) {
+        return apr_psprintf(cmd->pool, "ModSecurity: Invalid value for SecRequestBodyJsonDepthLimit: %s", p1);
+    }
+
+    dcfg->reqbody_json_depth_limit = limit;
+
+    return NULL;
+}
+
 static const char *cmd_request_body_access(cmd_parms *cmd, void *_dcfg,
                                            const char *p1)
 {
@@ -3553,6 +3575,14 @@ const command_rec module_directives[] = {
         "maximum request body size ModSecurity will accept, but excluding the size of uploaded files."
     ),
 
+    AP_INIT_TAKE1 (
+        "SecRequestBodyJsonDepthLimit",
+        cmd_request_body_json_depth_limit,
+        NULL,
+        CMD_SCOPE_ANY,
+        "maximum request body JSON parsing depth ModSecurity will accept."
+    ),
+
     AP_INIT_TAKE1 (
         "SecRequestEncoding",
         cmd_request_encoding,

apache2/modsecurity.h

@@ -95,6 +95,7 @@ typedef struct msc_parm msc_parm;
 #define REQUEST_BODY_DEFAULT_INMEMORY_LIMIT     131072
 #define REQUEST_BODY_DEFAULT_LIMIT              134217728
 #define REQUEST_BODY_NO_FILES_DEFAULT_LIMIT     1048576
+#define REQUEST_BODY_JSON_DEPTH_DEFAULT_LIMIT   10000
 #define RESPONSE_BODY_DEFAULT_LIMIT             524288
 #define RESPONSE_BODY_HARD_LIMIT                1073741824L
 
@@ -498,6 +499,7 @@ struct directory_config {
     long int             reqbody_inmemory_limit;
     long int             reqbody_limit;
     long int             reqbody_no_files_limit;
+    long int             reqbody_json_depth_limit;
     int                  resbody_access;
 
     long int             of_limit;

apache2/msc_json.c

@@ -164,6 +164,11 @@ static int yajl_start_array(void *ctx) {
     else {
         msr->json->prefix = apr_pstrdup(msr->mp, msr->json->current_key);
     }
+    msr->json->current_depth++;
+    if (msr->json->current_depth > msr->txcfg->reqbody_json_depth_limit) {
+        msr->json->depth_limit_exceeded = 1;
+	return 0;
+    }
 
     if (msr->txcfg->debuglog_level >= 9) {
         msr_log(msr, 9, "New JSON hash context (prefix '%s')", msr->json->prefix);
@@ -200,6 +205,7 @@ static int yajl_end_array(void *ctx) {
          */
         msr->json->prefix = (unsigned char *) NULL;
     }
+    msr->json->current_depth--;
 
     return 1;
 }
@@ -229,6 +235,11 @@ static int yajl_start_map(void *ctx)
     else {
         msr->json->prefix = apr_pstrdup(msr->mp, msr->json->current_key);
     }
+    msr->json->current_depth++;
+    if (msr->json->current_depth > msr->txcfg->reqbody_json_depth_limit) {
+        msr->json->depth_limit_exceeded = 1;
+	return 0;
+    }
 
     if (msr->txcfg->debuglog_level >= 9) {
         msr_log(msr, 9, "New JSON hash context (prefix '%s')", msr->json->prefix);
@@ -270,6 +281,7 @@ static int yajl_end_map(void *ctx)
         msr->json->current_key = msr->json->prefix;
         msr->json->prefix = (unsigned char *) NULL;
     }
+    msr->json->current_depth--;
 
     return 1;
 }
@@ -308,6 +320,9 @@ int json_init(modsec_rec *msr, char **error_msg) {
     msr->json->prefix = (unsigned char *) NULL;
     msr->json->current_key = (unsigned char *) NULL;
 
+    msr->json->current_depth = 0;
+    msr->json->depth_limit_exceeded = 0;
+
     /**
      * yajl initialization
      *
@@ -337,7 +352,11 @@ int json_process_chunk(modsec_rec *msr, const char *buf, unsigned int size, char
     msr->json->status = yajl_parse(msr->json->handle, buf, size);
     if (msr->json->status != yajl_status_ok) {
         /* We need to free the yajl error message later, how to do this? */
-        *error_msg = yajl_get_error(msr->json->handle, 0, buf, size);
+	if (msr->json->depth_limit_exceeded) {
+           *error_msg = "JSON depth limit exceeded";
+	} else {
+           *error_msg = yajl_get_error(msr->json->handle, 0, NULL, 0);
+	}
         return -1;
     }
 
@@ -357,7 +376,12 @@ int json_complete(modsec_rec *msr, char **error_msg) {
     msr->json->status = yajl_complete_parse(msr->json->handle);
     if (msr->json->status != yajl_status_ok) {
         /* We need to free the yajl error message later, how to do this? */
-        *error_msg = yajl_get_error(msr->json->handle, 0, NULL, 0);
+	if (msr->json->depth_limit_exceeded) {
+           *error_msg = "JSON depth limit exceeded";
+	} else {
+           *error_msg = yajl_get_error(msr->json->handle, 0, NULL, 0);
+	}
+
         return -1;
     }
 

apache2/msc_json.h

@@ -40,6 +40,8 @@ struct json_data {
     /* prefix is used to create data hierarchy (i.e., 'parent.child.value') */
     unsigned char *prefix;
     unsigned char *current_key;
+    long int current_depth;
+    int depth_limit_exceeded;
 };
 
 /* Functions */