From 45bf0bd0627d9f5ab9d2dda56f4946bc507b26b3 Mon Sep 17 00:00:00 2001
From: Vincent Bernat <bernat@luffy.cx>
Date: Sun, 15 Dec 2013 13:07:19 +0100
Subject: [PATCH] lldpd: use vfork+exec instead of fork+exec

This will help compatibility with systems not having a working `fork()`
implementation. For those who do, we will still use `fork()`.
---
 configure.ac       |  1 +
 src/daemon/lldpd.c | 41 ++++++++++++++++++++---------------------
 src/daemon/lldpd.h |  7 +++++++
 3 files changed, 28 insertions(+), 21 deletions(-)

diff --git a/configure.ac b/configure.ac
index 553a17c3..dcaaaa60 100644
--- a/configure.ac
+++ b/configure.ac
@@ -101,6 +101,7 @@ lldp_CHECK_ALIGNOF
 AC_CONFIG_LIBOBJ_DIR([src/compat])
 AC_FUNC_MALLOC
 AC_FUNC_REALLOC
+AC_FUNC_FORK
 AC_SEARCH_LIBS([setproctitle], [util bsd])
 AC_REPLACE_FUNCS([setproctitle])
 AC_CHECK_FUNCS([setproctitle_init])
diff --git a/src/daemon/lldpd.c b/src/daemon/lldpd.c
index eff4455c..f3cc7fe1 100644
--- a/src/daemon/lldpd.c
+++ b/src/daemon/lldpd.c
@@ -645,11 +645,11 @@ lldpd_get_lsb_release() {
 		return NULL;
 	}
 
-	if ((pid = fork()) < 0) {
+	pid = vfork();
+	switch (pid) {
+	case -1:
 		log_warn("localchassis", "unable to fork");
 		return NULL;
-	}
-	switch (pid) {
 	case 0:
 		/* Child, exec lsb_release */
 		close(pipefd[0]);
@@ -661,7 +661,7 @@ lldpd_get_lsb_release() {
 			if (pipefd[1] > 2) close(pipefd[1]);
 			execvp("lsb_release", command);
 		}
-		exit(127);
+		_exit(127);
 		break;
 	default:
 		/* Father, read the output from the children */
@@ -1108,9 +1108,15 @@ lldpd_exit(struct lldpd *cfg)
 static pid_t
 lldpd_configure(int debug, const char *path, const char *ctlname)
 {
-	pid_t lldpcli = fork();
+	pid_t lldpcli = vfork();
 	int devnull;
 
+	char sdebug[debug + 3];
+	memset(sdebug, 'd', debug + 3);
+	sdebug[debug + 2] = '\0';
+	sdebug[0] = '-'; sdebug[1] = 's';
+	log_debug("main", "invoke %s %s", path, sdebug);
+
 	switch (lldpcli) {
 	case -1:
 		log_warn("main", "unable to fork");
@@ -1118,27 +1124,20 @@ lldpd_configure(int debug, const char *path, const char *ctlname)
 	case 0:
 		/* Child, exec lldpcli */
 		if ((devnull = open("/dev/null", O_RDWR, 0)) != -1) {
-			char sdebug[debug + 3];
-			memset(sdebug, 'd', debug + 3);
-			sdebug[debug + 2] = '\0';
-			sdebug[0] = '-'; sdebug[1] = 's';
-
 			dup2(devnull,   STDIN_FILENO);
 			dup2(devnull,   STDOUT_FILENO);
 			if (devnull > 2) close(devnull);
 
-			log_debug("main", "invoke %s %s", path, sdebug);
-			if (execl(path, "lldpcli", sdebug,
-				"-u", ctlname,
-				"-c", SYSCONFDIR "/lldpd.conf",
-				"-c", SYSCONFDIR "/lldpd.d",
-				"resume",
-				NULL) == -1) {
-				log_warn("main", "unable to execute %s", path);
-				log_warnx("main", "configuration is incomplete, lldpd needs to be unpaused");
-			}
+			execl(path, "lldpcli", sdebug,
+			    "-u", ctlname,
+			    "-c", SYSCONFDIR "/lldpd.conf",
+			    "-c", SYSCONFDIR "/lldpd.d",
+			    "resume",
+			    NULL);
+			log_warn("main", "unable to execute %s", path);
+			log_warnx("main", "configuration is incomplete, lldpd needs to be unpaused");
 		}
-		exit(127);
+		_exit(127);
 		break;
 	default:
 		/* Father, don't do anything stupid */
diff --git a/src/daemon/lldpd.h b/src/daemon/lldpd.h
index 56835763..38bb0fbf 100644
--- a/src/daemon/lldpd.h
+++ b/src/daemon/lldpd.h
@@ -38,6 +38,13 @@
 #include <netinet/in.h>
 #include <sys/un.h>
 
+#if HAVE_VFORK_H
+# include <vfork.h>
+#endif
+#if HAVE_WORKING_FORK
+# define vfork fork
+#endif
+
 #include "lldp-tlv.h"
 #if defined (ENABLE_CDP) || defined (ENABLE_FDP)
 #  include "cdp.h"
-- 
2.39.5