fix ajp_msg_check_header check

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1933347 13f79535-47bb-0310-9956-ffa450edef68

Author: covener

modules/proxy/ajp_msg.c

@@ -166,11 +166,11 @@ apr_status_t ajp_msg_check_header(ajp_msg_t *msg, apr_size_t *len)
     msglen  = ((head[2] & 0xff) << 8);
     msglen += (head[3] & 0xFF);
 
-    if (msglen > msg->max_size) {
+    if (msglen > (msg->max_size - AJP_HEADER_LEN)) {
         ap_log_error(APLOG_MARK, APLOG_ERR, 0, NULL, APLOGNO(01081)
                      "ajp_msg_check_header() incoming message is "
                      "too big %" APR_SIZE_T_FMT ", max is %" APR_SIZE_T_FMT,
-                     msglen, msg->max_size);
+                     msglen, msg->max_size - AJP_HEADER_LEN);
         return AJP_ETOBIG;
     }