add support for the newline-fd readiness protocol

Signed-off-by: Carlos Eduardo <[email protected]>

platform.c

@@ -33,6 +33,7 @@
 #include "openbsd-compat/openbsd-compat.h"
 
 extern int use_privsep;
+extern int notify_fd;
 extern ServerOptions options;
 
 void
@@ -47,6 +48,12 @@ platform_pre_listen(void)
 void
 platform_post_listen(void)
 {
+	if (notify_fd) {
+		/* newline notification */
+		write(STDOUT_FILENO, "\n", 1);
+		/* close stdout */
+		dup2(STDERR_FILENO, STDOUT_FILENO);
+	}
 #ifdef SYSTEMD_NOTIFY
 	ssh_systemd_notify_ready();
 #endif

sshd.c

@@ -150,6 +150,11 @@ char *config_file_name = _PATH_SERVER_CONFIG_FILE;
  */
 int debug_flag = 0;
 
+/*
+ * Write a newline to stdout after listening.
+ */
+int notify_fd = 0;
+
 /*
  * Indicating that the daemon should only test the configuration and keys.
  * If test_flag > 1 ("-T" flag), then sshd will also dump the effective
@@ -896,7 +901,7 @@ usage(void)
 {
 	fprintf(stderr, "%s, %s\n", SSH_RELEASE, SSH_OPENSSL_VERSION);
 	fprintf(stderr,
-"usage: sshd [-46DdeGiqTtV] [-C connection_spec] [-c host_cert_file]\n"
+"usage: sshd [-46DdeGiqTtV3] [-C connection_spec] [-c host_cert_file]\n"
 "            [-E log_file] [-f config_file] [-g login_grace_time]\n"
 "            [-h host_key_file] [-o option] [-p port] [-u len]\n"
 	);
@@ -1591,7 +1596,7 @@ main(int ac, char **av)
 
 	/* Parse command-line arguments. */
 	while ((opt = getopt(ac, av,
-	    "C:E:b:c:f:g:h:k:o:p:u:46DGQRTdeiqrtV")) != -1) {
+	    "C:E:b:c:f:g:h:k:o:p:u:46DGQRTdeiqrtV3")) != -1) {
 		switch (opt) {
 		case '4':
 			options.address_family = AF_INET;
@@ -1699,6 +1704,11 @@ main(int ac, char **av)
 			fprintf(stderr, "%s, %s\n",
 			    SSH_RELEASE, SSH_OPENSSL_VERSION);
 			exit(0);
+		case '3':
+			/* implies process will be supervised */
+			no_daemon_flag = 1;
+			notify_fd = 1;
+			break;
 		default:
 			usage();
 			break;
@@ -1708,10 +1718,12 @@ main(int ac, char **av)
 		rexec_flag = 0;
 	if (!test_flag && !do_dump_cfg && rexec_flag && !path_absolute(av[0]))
 		fatal("sshd re-exec requires execution with an absolute path");
-	if (rexeced_flag)
+	if (rexeced_flag) {
+		notify_fd = 0;
 		closefrom(REEXEC_MIN_FREE_FD);
-	else
+	} else {
 		closefrom(REEXEC_DEVCRYPTO_RESERVED_FD);
+	}
 
 	seed_rng();