Merge pull request #3532 from alliedtelesis/fix_lxc_attach_crash

src/lxc/attach.c

@@ -1384,8 +1384,7 @@ int lxc_attach(struct lxc_container *container, lxc_attach_exec_t exec_function,
 
 	if (pid == 0) {
 		if (options->attach_flags & LXC_ATTACH_TERMINAL) {
-			ret = pthread_sigmask(SIG_SETMASK,
-					      &terminal.tty_state->oldmask, NULL);
+			ret = lxc_terminal_signal_sigmask_safe_blocked(&terminal);
 			if (ret < 0) {
 				SYSERROR("Failed to reset signal mask");
 				_exit(EXIT_FAILURE);

src/lxc/terminal.c

@@ -147,6 +147,16 @@ struct lxc_terminal_state *lxc_terminal_signal_init(int srcfd, int dstfd)
 	return move_ptr(ts);
 }
 
+int lxc_terminal_signal_sigmask_safe_blocked(struct lxc_terminal *terminal)
+{
+	struct lxc_terminal_state *state = terminal->tty_state;
+
+	if (!state)
+		return 0;
+
+	return pthread_sigmask(SIG_SETMASK, &state->oldmask, NULL);
+}
+
 /**
  * lxc_terminal_signal_fini: uninstall signal handler
  *

src/lxc/terminal.h

@@ -251,5 +251,6 @@ __hidden extern int lxc_terminal_prepare_login(int fd);
 __hidden extern void lxc_terminal_conf_free(struct lxc_terminal *terminal);
 __hidden extern void lxc_terminal_info_init(struct lxc_terminal_info *terminal);
 __hidden extern void lxc_terminal_init(struct lxc_terminal *terminal);
+__hidden extern int lxc_terminal_signal_sigmask_safe_blocked(struct lxc_terminal *terminal);
 
 #endif /* __LXC_TERMINAL_H */