attach: reset signal mask

Since we introduced clean exit from the mainloop when SIGTERM is sent we
changed the signal mask of the parent process but we never reset the
signal mask for the actual attached process.

Closes #399.

Fixes: 1349e92 ("console: exit mainloop on SIGTERM")
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

src/lxc/attach.c

@@ -1483,6 +1483,15 @@ int lxc_attach(const char *name, const char *lxcpath,
 	}
 
 	if (pid == 0) {
+		if (options->attach_flags & LXC_ATTACH_TERMINAL) {
+			ret = pthread_sigmask(SIG_SETMASK,
+					      &terminal.tty_state->oldmask, NULL);
+			if (ret < 0) {
+				SYSERROR("Failed to reset signal mask");
+				_exit(EXIT_FAILURE);
+			}
+		}
+
 		ret = attach_child_main(&payload);
 		if (ret < 0)
 			ERROR("Failed to exec");