fix nasty expired pointer

us.c

@@ -102,12 +102,14 @@ int main(int argc, char *argv[])
 		fprintf(stderr, "getpwid: %s\n", strerror(errno));
 		return errno;
 	}
+	char *my_name = strdup(my_pw->pw_name);
+	if (!my_name)
+		die("strdup:");
 
 	/* Authenticate, we will be root from now on */
 	if (authenticate(my_pw->pw_uid, 0))
 		exit(EXIT_FAILURE);
 
-
 	/* Get target user and group info */
 	t_pw = user_to_passwd(t_usr);
 	if (!t_pw)
@@ -169,8 +171,11 @@ int main(int argc, char *argv[])
 	};
 
 	if (envflag) {	/* clear env */
-		for (int i = 0; env_keep[i].name; i++)
+		for (int i = 0; env_keep[i].name; i++) {
 			env_keep[i].value = strdup(getenv(env_keep[i].name));
+			if (!env_keep[i].value)
+				die("strdup:");
+		}
 		environ = NULL; // in place of clearenv
 	}
 
@@ -194,7 +199,8 @@ int main(int argc, char *argv[])
 		}
 	}
 	// do not override, we might be under more levels of 'us'
-	err = setenv("US_USER", my_pw->pw_name, 0);
+	err = setenv("US_USER", my_name, 0);
+	free(my_name);
 
 	errno = 0;
 	/* Set permissions */