optionsfrom: Properly handle errors when determining file size

src/libstrongswan/utils/optionsfrom.c

@@ -90,8 +90,13 @@ METHOD(options_t, from, bool,
 	}
 
 	/* determine the file size */
-	fseek(fd, 0, SEEK_END);
+	if (fseek(fd, 0, SEEK_END) == -1 || (src.len = ftell(fd)) == -1)
-	src.len = ftell(fd);
+	{
+		DBG1(DBG_LIB, "optionsfrom: unable to determine size of '%s': %s",
+			 filename, strerror(errno));
+		fclose(fd);
+		return FALSE;
+	}
 	rewind(fd);
 
 	/* allocate one byte more just in case of a missing final newline */