GUACAMOLE-474: Enforce download disable option at low level, warning if not blocked at higher level as expected.

src/common-ssh/sftp.c

@@ -516,6 +516,15 @@ guac_stream* guac_common_ssh_sftp_download_file(
     guac_stream* stream;
     LIBSSH2_SFTP_HANDLE* file;
 
+    /* Ignore download if downloads have been disabled */
+    if (filesystem->disable_download) {
+        guac_user_log(user, GUAC_LOG_WARNING, "A download attempt has "
+                "been blocked due to downloads being disabled, however it "
+                "should have been blocked at a higher level. This is likely "
+                "a bug.");
+        return NULL;
+    }
+
     /* Attempt to open file for reading */
     file = libssh2_sftp_open(filesystem->sftp_session, filename,
             LIBSSH2_FXF_READ, 0);

src/protocols/rdp/download.c

@@ -185,6 +185,15 @@ void* guac_rdp_download_to_user(guac_user* user, void* data) {
     if (filesystem == NULL)
         return NULL;
 
+    /* Ignore download if downloads have been disabled */
+    if (filesystem->disable_download) {
+        guac_client_log(client, GUAC_LOG_WARNING, "A download attempt has "
+                "been blocked due to downloads being disabled, however it "
+                "should have been blocked at a higher level. This is likely "
+                "a bug.");
+        return NULL;
+    }
+
     /* Attempt to open requested file */
     char* path = (char*) data;
     int file_id = guac_rdp_fs_open(filesystem, path,