From d4da20f064f4d155ad27f1595893e5b0a6c4c5e1 Mon Sep 17 00:00:00 2001
From: Simon Kelley <simon@thekelleys.org.uk>
Date: Fri, 4 Oct 2013 10:12:49 +0100
Subject: [PATCH] Unset environment variables to script when we have no value
 for them.

---
 src/helper.c | 93 ++++++++++++++++++++++++++--------------------------
 1 file changed, 46 insertions(+), 47 deletions(-)

diff --git a/src/helper.c b/src/helper.c
index 5872e6a..24c2afd 100644
--- a/src/helper.c
+++ b/src/helper.c
@@ -481,20 +481,13 @@ int create_helper(int event_fd, int err_fd, uid_t uid, gid_t gid, long max_fd)
       if (data.action != ACTION_TFTP)
 	{
 #ifdef HAVE_DHCP6
-	  if (is6)
-	    {
-	      my_setenv("DNSMASQ_IAID", daemon->dhcp_buff3, &err);
-	      my_setenv("DNSMASQ_SERVER_DUID", daemon->dhcp_packet.iov_base, &err); 
-	      if (data.hwaddr_len != 0)
-		my_setenv("DNSMASQ_MAC", daemon->dhcp_buff, &err);
-	    }
+	  my_setenv("DNSMASQ_IAID", is6 ? daemon->dhcp_buff3 : NULL, &err);
+	  my_setenv("DNSMASQ_SERVER_DUID", is6 ? daemon->dhcp_packet.iov_base : NULL, &err); 
+	  my_setenv("DNSMASQ_MAC", is6 && data.hwaddr_len != 0 ? daemon->dhcp_buff : NULL, &err);
 #endif
 	  
-	  if (!is6 && data.clid_len != 0)
-	    my_setenv("DNSMASQ_CLIENT_ID", daemon->packet, &err);
-	  
-	  if (strlen(data.interface) != 0)
-	    my_setenv("DNSMASQ_INTERFACE", data.interface, &err);
+	  my_setenv("DNSMASQ_CLIENT_ID", !is6 && data.clid_len != 0 ? daemon->packet : NULL, &err);
+	  my_setenv("DNSMASQ_INTERFACE", strlen(data.interface) != 0 ? data.interface : NULL, &err);
 	  
 #ifdef HAVE_BROKEN_RTC
 	  sprintf(daemon->dhcp_buff2, "%u", data.length);
@@ -504,8 +497,7 @@ int create_helper(int event_fd, int err_fd, uid_t uid, gid_t gid, long max_fd)
 	  my_setenv("DNSMASQ_LEASE_EXPIRES", daemon->dhcp_buff2, &err); 
 #endif
 	  
-	  if (domain)
-	    my_setenv("DNSMASQ_DOMAIN", domain, &err);
+	  my_setenv("DNSMASQ_DOMAIN", domain, &err);
 	  
 	  end = extradata + data.ed_len;
 	  buf = extradata;
@@ -543,8 +535,8 @@ int create_helper(int event_fd, int err_fd, uid_t uid, gid_t gid, long max_fd)
 
 	  if (is6)
 	    buf = grab_extradata(buf, end, "DNSMASQ_RELAY_ADDRESS", &err);
-	  else if (data.giaddr.s_addr != 0)
-	    my_setenv("DNSMASQ_RELAY_ADDRESS", inet_ntoa(data.giaddr), &err); 
+	  else 
+	    my_setenv("DNSMASQ_RELAY_ADDRESS", data.giaddr.s_addr != 0 ? inet_ntoa(data.giaddr) : NULL, &err); 
 	  
 	  for (i = 0; buf; i++)
 	    {
@@ -552,22 +544,16 @@ int create_helper(int event_fd, int err_fd, uid_t uid, gid_t gid, long max_fd)
 	      buf = grab_extradata(buf, end, daemon->dhcp_buff2, &err);
 	    }
 	  
-	  if (data.action != ACTION_DEL && data.remaining_time != 0)
-	    {
-	      sprintf(daemon->dhcp_buff2, "%u", data.remaining_time);
-	      my_setenv("DNSMASQ_TIME_REMAINING", daemon->dhcp_buff2, &err);
-	    }
+	  sprintf(daemon->dhcp_buff2, "%u", data.remaining_time);
+	  my_setenv("DNSMASQ_TIME_REMAINING", data.action != ACTION_DEL && data.remaining_time != 0 ? daemon->dhcp_buff2 : NULL, &err);
 	  
-	  if (data.action == ACTION_OLD_HOSTNAME && hostname)
-	    {
-	      my_setenv("DNSMASQ_OLD_HOSTNAME", hostname, &err);
-	      hostname = NULL;
-	    }
+	  my_setenv("DNSMASQ_OLD_HOSTNAME", data.action == ACTION_OLD_HOSTNAME ? hostname : NULL, &err);
+	  if (data.action == ACTION_OLD_HOSTNAME)
+	    hostname = NULL;
 	}
 
-      if (option_bool(OPT_LOG_OPTS))
-	my_setenv("DNSMASQ_LOG_DHCP", "1", &err);
-	 
+      my_setenv("DNSMASQ_LOG_DHCP", option_bool(OPT_LOG_OPTS) ? "1" : NULL, &err);
+      
       /* we need to have the event_fd around if exec fails */
       if ((i = fcntl(event_fd, F_GETFD)) != -1)
 	fcntl(event_fd, F_SETFD, i | FD_CLOEXEC);
@@ -590,31 +576,44 @@ int create_helper(int event_fd, int err_fd, uid_t uid, gid_t gid, long max_fd)
 
 static void my_setenv(const char *name, const char *value, int *error)
 {
-  if (*error == 0 && setenv(name, value, 1) != 0)
-    *error = errno;
+  if (*error == 0)
+    {
+      if (!value)
+	unsetenv(name);
+      else if (setenv(name, value, 1) != 0)
+	*error = errno;
+    }
 }
  
 static unsigned char *grab_extradata(unsigned char *buf, unsigned char *end,  char *env, int *err)
 {
-  unsigned char *next;
+  unsigned char *next = NULL;
+  char *val = NULL;
 
-  if (!buf || (buf == end))
-    return NULL;
-
-  for (next = buf; *next != 0; next++)
-    if (next == end)
-      return NULL;
-  
-  if (next != buf)
+  if (buf && (buf != end))
     {
-      char *p;
-      /* No "=" in value */
-      if ((p = strchr((char *)buf, '=')))
-	*p = 0;
-      my_setenv(env, (char *)buf, err);
-    }
+      for (next = buf; ; next++)
+	if (next == end)
+	  {
+	    next = NULL;
+	    break;
+	  }
+	else if (*next == 0)
+	  break;
 
-  return next + 1;
+      if (next && (next != buf))
+	{
+	  char *p;
+	  /* No "=" in value */
+	  if ((p = strchr((char *)buf, '=')))
+	    *p = 0;
+	  val = (char *)buf;
+	}
+    }
+  
+  my_setenv(env, val, err);
+   
+  return next ? next + 1 : NULL;
 }
 
 #ifdef HAVE_LUASCRIPT