3 files changed, 29 insertions, 9 deletions

diff --git a/misc.c b/misc.c
index 07d4179e4..65c9222aa 100644
--- a/misc.c
+++ b/misc.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: misc.c,v 1.106 2016/10/23 22:04:05 dtucker Exp $ */
+/* $OpenBSD: misc.c,v 1.107 2016/11/30 00:28:31 dtucker Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  * Copyright (c) 2005,2006 Damien Miller.  All rights reserved.
@@ -1251,3 +1251,21 @@ bind_permitted(int port, uid_t uid)
                 return 0;
         return 1;
 }
+
+/* returns 1 if process is already daemonized, 0 otherwise */
+int
+daemonized(void)
+{
+        int fd;
+
+        if ((fd = open(_PATH_TTY, O_RDONLY | O_NOCTTY)) >= 0) {
+                close(fd);
+                return 0;       /* have controlling terminal */
+        }
+        if (getppid() != 1)
+                return 0;       /* parent is not init */
+        if (getsid(0) != getpid())
+                return 0;       /* not session leader */
+        debug3("already daemonized");
+        return 1;
+}
diff --git a/misc.h b/misc.h
index 3578e8ef5..c242f9011 100644
--- a/misc.h
+++ b/misc.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: misc.h,v 1.60 2016/10/23 22:04:05 dtucker Exp $ */
+/* $OpenBSD: misc.h,v 1.61 2016/11/30 00:28:31 dtucker Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -31,6 +31,7 @@ struct Forward {
 
 int forward_equals(const struct Forward *, const struct Forward *);
 int bind_permitted(int, uid_t);
+int daemonized(void);
 
 /* Common server and client forwarding options. */
 struct ForwardOptions {
diff --git a/sshd.c b/sshd.c
index ce4a493ef..fafcd3400 100644
--- a/sshd.c
+++ b/sshd.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshd.c,v 1.477 2016/11/29 03:54:50 dtucker Exp $ */
+/* $OpenBSD: sshd.c,v 1.478 2016/11/30 00:28:31 dtucker Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -1343,7 +1343,7 @@ main(int ac, char **av)
         struct ssh *ssh = NULL;
         extern char *optarg;
         extern int optind;
-        int r, opt, i, j, on = 1;
+        int r, opt, i, j, on = 1, already_daemon;
         int sock_in = -1, sock_out = -1, newsock = -1;
         const char *remote_ip;
         int remote_port;
@@ -1802,11 +1802,12 @@ main(int ac, char **av)
         log_init(__progname, options.log_level, options.log_facility, log_stderr);
 
         /*
-         * If not in debugging mode, and not started from inetd, disconnect
-         * from the controlling terminal, and fork.  The original process
-         * exits.
+         * If not in debugging mode, not started from inetd and not already
+         * daemonized (eg re-exec via SIGHUP), disconnect from the controlling
+         * terminal, and fork.  The original process exits.
          */
-        if (!(debug_flag || inetd_flag || no_daemon_flag)) {
+        already_daemon = daemonized();
+        if (!(debug_flag || inetd_flag || no_daemon_flag || already_daemon)) {
 
                 if (daemon(0, 0) < 0)
                         fatal("daemon() failed: %.200s", strerror(errno));
@@ -1840,7 +1841,7 @@ main(int ac, char **av)
                  * Write out the pid file after the sigterm handler
                  * is setup and the listen sockets are bound
                  */
-                if (options.pid_file != NULL && !debug_flag) {
+                if (options.pid_file != NULL && !debug_flag && !already_daemon) {
                         FILE *f = fopen(options.pid_file, "w");
 
                         if (f == NULL) {