Merge pull request #2933 from brauner/2019-04-13/pdeath_signal_fixes

src/lxc/start.c

@@ -709,6 +709,9 @@ void lxc_free_handler(struct lxc_handler *handler)
 		if (handler->conf->maincmd_fd >= 0)
 			lxc_abstract_unix_close(handler->conf->maincmd_fd);
 
+	if (handler->monitor_status_fd >= 0)
+		close(handler->monitor_status_fd);
+
 	if (handler->state_socket_pair[0] >= 0)
 		close(handler->state_socket_pair[0]);
 
@@ -743,6 +746,7 @@ struct lxc_handler *lxc_init_handler(const char *name, struct lxc_conf *conf,
 	handler->data_sock[0] = handler->data_sock[1] = -1;
 	handler->conf = conf;
 	handler->lxcpath = lxcpath;
+	handler->monitor_status_fd = -EBADF;
 	handler->pinfd = -1;
 	handler->pidfd = -EBADF;
 	handler->proc_pidfd = -EBADF;
@@ -795,11 +799,17 @@ on_error:
 
 int lxc_init(const char *name, struct lxc_handler *handler)
 {
+	__do_close_prot_errno int status_fd = -EBADF;
 	int ret;
 	const char *loglevel;
 	struct lxc_conf *conf = handler->conf;
 
 	handler->monitor_pid = lxc_raw_getpid();
+	status_fd = open("/proc/self/status", O_RDONLY | O_CLOEXEC);
+	if (status_fd < 0) {
+		SYSERROR("Failed to open monitor status fd");
+		goto out_close_maincmd_fd;
+	}
 
 	lsm_init();
 	TRACE("Initialized LSM");
@@ -930,6 +940,7 @@ int lxc_init(const char *name, struct lxc_handler *handler)
 	TRACE("Initialized LSM");
 
 	INFO("Container \"%s\" is initialized", name);
+	handler->monitor_status_fd = move_fd(status_fd);
 	return 0;
 
 out_destroy_cgroups:
@@ -1131,6 +1142,7 @@ static int do_start(void *data)
 	struct lxc_handler *handler = data;
 	ATTR_UNUSED __do_close_prot_errno int data_sock0 = handler->data_sock[0],
 					      data_sock1 = handler->data_sock[1];
+	__do_close_prot_errno int status_fd = -EBADF;
 	int ret;
 	uid_t new_uid;
 	gid_t new_gid;
@@ -1141,13 +1153,18 @@ static int do_start(void *data)
 
 	lxc_sync_fini_parent(handler);
 
+	if (lxc_abstract_unix_recv_fds(handler->data_sock[1], &status_fd, 1, NULL, 0) < 0) {
+		ERROR("Failed to receive status file descriptor to child process");
+		goto out_warn_father;
+	}
+
 	/* This prctl must be before the synchro, so if the parent dies before
 	 * we set the parent death signal, we will detect its death with the
 	 * synchro right after, otherwise we have a window where the parent can
 	 * exit before we set the pdeath signal leading to a unsupervized
 	 * container.
 	 */
-	ret = lxc_set_death_signal(SIGKILL, handler->monitor_pid);
+	ret = lxc_set_death_signal(SIGKILL, handler->monitor_pid, status_fd);
 	if (ret < 0) {
 		SYSERROR("Failed to set PR_SET_PDEATHSIG to SIGKILL");
 		goto out_warn_father;
@@ -1227,7 +1244,7 @@ static int do_start(void *data)
 			goto out_warn_father;
 
 		/* set{g,u}id() clears deathsignal */
-		ret = lxc_set_death_signal(SIGKILL, handler->monitor_pid);
+		ret = lxc_set_death_signal(SIGKILL, handler->monitor_pid, status_fd);
 		if (ret < 0) {
 			SYSERROR("Failed to set PR_SET_PDEATHSIG to SIGKILL");
 			goto out_warn_father;
@@ -1481,7 +1498,8 @@ static int do_start(void *data)
 	}
 
 	if (handler->conf->monitor_signal_pdeath != SIGKILL) {
-		ret = lxc_set_death_signal(handler->conf->monitor_signal_pdeath, handler->monitor_pid);
+		ret = lxc_set_death_signal(handler->conf->monitor_signal_pdeath,
+					   handler->monitor_pid, status_fd);
 		if (ret < 0) {
 			SYSERROR("Failed to set PR_SET_PDEATHSIG to %d",
 				 handler->conf->monitor_signal_pdeath);
@@ -1787,6 +1805,12 @@ static int lxc_spawn(struct lxc_handler *handler)
 
 	lxc_sync_fini_child(handler);
 
+	if (lxc_abstract_unix_send_fds(handler->data_sock[0], &handler->monitor_status_fd, 1, NULL, 0) < 0) {
+		ERROR("Failed to send status file descriptor to child process");
+		goto out_delete_net;
+	}
+	close_prot_errno_disarm(handler->monitor_status_fd);
+
 	/* Map the container uids. The container became an invalid userid the
 	 * moment it was cloned with CLONE_NEWUSER. This call doesn't change
 	 * anything immediately, but allows the container to setuid(0) (0 being

src/lxc/start.h

@@ -114,6 +114,8 @@ struct lxc_handler {
 	/* The monitor's pid. */
 	pid_t monitor_pid;
 
+	int monitor_status_fd;
+
 	/* Whether the child has already exited. */
 	bool init_died;
 

src/lxc/utils.c

@@ -1728,7 +1728,43 @@ uint64_t lxc_find_next_power2(uint64_t n)
 	return n;
 }
 
-int lxc_set_death_signal(int signal, pid_t parent)
+static int process_dead(/* takes */ int status_fd)
+{
+	__do_close_prot_errno int dupfd = -EBADF;
+	__do_free char *line = NULL;
+	__do_fclose FILE *f = NULL;
+	int ret = 0;
+	size_t n = 0;
+
+	dupfd = dup(status_fd);
+	if (dupfd < 0)
+		return -1;
+
+	if (fd_cloexec(dupfd, true) < 0)
+		return -1;
+
+	/* transfer ownership of fd */
+	f = fdopen(move_fd(dupfd), "re");
+	if (!f)
+		return -1;
+
+	ret = 0;
+	while (getline(&line, &n, f) != -1) {
+		char *state;
+
+		if (strncmp(line, "State:", 6))
+			continue;
+
+		state = lxc_trim_whitespace_in_place(line + 6);
+		/* only check whether process is dead or zombie for now */
+		if (*state == 'X' || *state == 'Z')
+			ret = 1;
+	}
+
+	return ret;
+}
+
+int lxc_set_death_signal(int signal, pid_t parent, int parent_status_fd)
 {
 	int ret;
 	pid_t ppid;
@@ -1736,12 +1772,16 @@ int lxc_set_death_signal(int signal, pid_t parent)
 	ret = prctl(PR_SET_PDEATHSIG, prctl_arg(signal), prctl_arg(0),
 		    prctl_arg(0), prctl_arg(0));
 
-	/* If not in a PID namespace, check whether we have been orphaned. */
+	/* verify that we haven't been orphaned in the meantime */
 	ppid = (pid_t)syscall(SYS_getppid);
-	if (ppid && ppid != parent) {
-		ret = raise(SIGKILL);
-		if (ret < 0)
-			return -1;
+	if (ppid == 0) { /* parent outside our pidns */
+		if (parent_status_fd < 0)
+			return 0;
+
+		if (process_dead(parent_status_fd) == 1)
+			return raise(SIGKILL);
+	} else if (ppid != parent) {
+		return raise(SIGKILL);
 	}
 
 	if (ret < 0)

src/lxc/utils.h

@@ -256,7 +256,7 @@ static inline uint64_t lxc_getpagesize(void)
 extern uint64_t lxc_find_next_power2(uint64_t n);
 
 /* Set a signal the child process will receive after the parent has died. */
-extern int lxc_set_death_signal(int signal, pid_t parent);
+extern int lxc_set_death_signal(int signal, pid_t parent, int parent_status_fd);
 extern int fd_cloexec(int fd, bool cloexec);
 extern int recursive_destroy(char *dirname);
 extern int lxc_setup_keyring(void);