Minor improvements in lease-tools

Limit max interface name to fit into buffer.
Make sure pointer have to be always positive.
Close socket after received reply.

contrib/lease-tools/dhcp_lease_time.c

@@ -83,7 +83,7 @@ static unsigned char *option_find1(unsigned char *p, unsigned char *end, int opt
           if (p >= end - 2)
             return NULL; /* malformed packet */
           opt_len = option_len(p);
-          if (p >= end - (2 + opt_len))
+          if (end - p >= (2 + opt_len))
             return NULL; /* malformed packet */
           if (*p == opt && opt_len >= minsize)
             return p;

contrib/lease-tools/dhcp_release.c

@@ -270,7 +270,8 @@ int main(int argc, char **argv)
   
   /* This voodoo fakes up a packet coming from the correct interface, which really matters for 
      a DHCP server */
-  strcpy(ifr.ifr_name, argv[1]);
+  strncpy(ifr.ifr_name, argv[1], sizeof(ifr.ifr_name)-1);
+  ifr.ifr_name[sizeof(ifr.ifr_name)-1] = '\0';
   if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, &ifr, sizeof(ifr)) == -1)
     {
       perror("cannot setup interface");

contrib/lease-tools/dhcp_release6.c

@@ -376,9 +376,12 @@ int send_release_packet(const char* iface, struct dhcp6_packet* packet)
             sleep(1);
             continue;
 	  }
+
+        close(sock);
         return result;
       }
 
+    close(sock);
     fprintf(stderr, "Response timed out\n");
     return -1;   
 }