Add --dnssec-timestamp option and facility.

CHANGELOG

@@ -67,6 +67,12 @@ version 2.73
 
 	    Fix broken DNSSEC validation of ECDSA signatures.
 
+	    Add --dnssec-timestamp option, which provides an automatic
+	    way to detect when the system time becomes valid after boot
+	    on systems without an RTC, whilst allowing DNS queries before the
+	    clock is valid so that NTP can run. Thanks to
+	    Kevin Darbyshire-Bryant for developing this idea.
+	
 	
 version 2.72
             Add ra-advrouter mode, for RFC-3775 mobile IPv6 support.

man/dnsmasq.8

@@ -674,6 +674,12 @@ that dnsmasq should be started with this flag when the platform determines that
 reliable time is established, a SIGHUP should be sent to dnsmasq, which enables time checking, and purges the cache of DNS records
 which have not been throughly checked.
 .TP
+.B --dnssec-timestamp=<path>
+Enables an alternative way of checking the validity of the system time for DNSSEC (see --dnssec-no-timecheck). In this case, the 
+system time is considered to be valid once it becomes later than the timestamp on the specified file. The file is created and 
+its timestamp set automatically by dnsmasq. The file must be stored on a persistent filesystem, so that it and its mtime are carried 
+over system restarts. 
+.TP
 .B --proxy-dnssec
 Copy the DNSSEC Authenticated Data bit from upstream servers to downstream clients and cache it.  This is an 
 alternative to having dnsmasq validate DNSSEC, but it depends on the security of the network between 

src/dnsmasq.c

@@ -58,6 +58,9 @@ int main (int argc, char **argv)
   struct dhcp_context *context;
   struct dhcp_relay *relay;
 #endif
+#ifdef HAVE_DNSSEC
+  int badtime;
+#endif
 
 #ifdef LOCALEDIR
   setlocale(LC_ALL, "");
@@ -370,6 +373,10 @@ int main (int argc, char **argv)
   if (baduser)
     die(_("unknown user or group: %s"), baduser, EC_BADCONF);
 
+#ifdef HAVE_DNSSEC  
+  badtime = setup_timestamp(ent_pw->pw_uid);
+#endif
+
   /* implement group defaults, "dip" if available, or group associated with uid */
   if (!daemon->group_set && !gp)
     {
@@ -689,6 +696,8 @@ int main (int argc, char **argv)
       my_syslog(LOG_INFO, _("DNSSEC validation enabled"));
       if (option_bool(OPT_DNSSEC_TIME))
 	my_syslog(LOG_INFO, _("DNSSEC signature timestamps not checked until first cache reload"));
+      if (badtime)
+	my_syslog(LOG_INFO, _("DNSSEC signature timestamps not checked until system time valid"));
     }
 #endif
 

src/dnsmasq.h

@@ -986,6 +986,7 @@ extern struct daemon {
 #endif
 #ifdef HAVE_DNSSEC
   struct ds_config *ds;
+  char *timestamp_file;
 #endif
 
   /* globally used stuff for DNS */
@@ -1151,6 +1152,7 @@ int dnssec_chase_cname(time_t now, struct dns_header *header, size_t plen, char
 int dnskey_keytag(int alg, int flags, unsigned char *rdata, int rdlen);
 size_t filter_rrsigs(struct dns_header *header, size_t plen);
 unsigned char* hash_questions(struct dns_header *header, size_t plen, char *name);
+int setup_timestamp(uid_t uid);
 
 /* util.c */
 void rand_init(void);

src/dnssec.c

@@ -34,6 +34,7 @@
 #include <nettle/dsa-compat.h>
 #endif
 
+#include <utime.h>
 
 #define SERIAL_UNDEF  -100
 #define SERIAL_EQ        0
@@ -394,16 +395,87 @@ static int serial_compare_32(unsigned long s1, unsigned long s2)
   return SERIAL_UNDEF;
 }
 
+/* Called at startup. If the timestamp file is configured and exists, put its mtime on
+   timestamp_time. If it doesn't exist, create it, and set the mtime to 1-1-2015.
+   Change the ownership to the user we'll be running as, so that we can update the mtime.
+*/
+static time_t timestamp_time;
+static int back_to_the_future;
+
+int setup_timestamp(uid_t uid)
+{
+  struct stat statbuf;
+  
+  back_to_the_future = 0;
+  
+  if (!option_bool(OPT_DNSSEC_VALID) || !daemon->timestamp_file)
+    return 0;
+  
+  if (stat(daemon->timestamp_file, &statbuf) != -1)
+    {
+      timestamp_time = statbuf.st_mtime;
+    check_and_exit:
+      if (difftime(timestamp_time, time(0)) <=  0)
+	{
+	  /* time already OK, update timestamp, and do key checking from the start. */
+	  if (utime(daemon->timestamp_file, NULL) == -1)
+	    my_syslog(LOG_ERR, _("failed to update mtime on %s: %s"), daemon->timestamp_file, strerror(errno));
+	  back_to_the_future = 1;
+	  return 0;
+	}
+      return 1;
+    }
+  
+  if (errno == ENOENT)
+    {
+      int fd = open(daemon->timestamp_file, O_WRONLY | O_CREAT | O_NONBLOCK, 0666);
+      if (fd != -1)
+	{
+	  struct utimbuf timbuf;
+
+	  close(fd);
+	  
+	  timestamp_time = timbuf.actime = timbuf.modtime = 1420070400; /* 1-1-2015 */
+	  if (utime(daemon->timestamp_file, &timbuf) == 0 &&
+	      (getuid() != 0 || chown(daemon->timestamp_file, uid, -1) == 0))
+	    goto check_and_exit;
+	}
+    }
+
+  die(_("Cannot create timestamp file %s: %s" ), daemon->timestamp_file, EC_BADCONF);
+  return 0;
+}
+
 /* Check whether today/now is between date_start and date_end */
 static int check_date_range(unsigned long date_start, unsigned long date_end)
 {
-  unsigned long curtime;
+  unsigned long curtime = time(0);
  
   /* Checking timestamps may be temporarily disabled */
-  if (option_bool(OPT_DNSSEC_TIME))
-    return 1;
     
-  curtime = time(0);
+  /* If the current time if _before_ the timestamp
+     on our persistent timestamp file, then assume the
+     time if not yet correct, and don't check the
+     key timestamps. As soon as the current time is
+     later then the timestamp, update the timestamp
+     and start checking keys */
+  if (daemon->timestamp_file)
+    {
+      if (back_to_the_future == 0 && difftime(timestamp_time, curtime) <= 0)
+	{
+	  if (utime(daemon->timestamp_file, NULL) != 0)
+	    my_syslog(LOG_ERR, _("failed to update mtime on %s: %s"), daemon->timestamp_file, strerror(errno));
+	  
+	  back_to_the_future = 1;	
+	  set_option_bool(OPT_DNSSEC_TIME);
+	  queue_event(EVENT_RELOAD); /* purge cache */
+	} 
+
+      if (back_to_the_future == 0)
+	return 1;
+    }
+  else if (option_bool(OPT_DNSSEC_TIME))
+    return 1;
   
   /* We must explicitly check against wanted values, because of SERIAL_UNDEF */
   return serial_compare_32(curtime, date_start) == SERIAL_GT

src/option.c

@@ -152,6 +152,7 @@ struct myoption {
 #define LOPT_DHCP_INOTIFY  340
 #define LOPT_DHOPT_INOTIFY 341
 #define LOPT_HOST_INOTIFY  342
+#define LOPT_DNSSEC_STAMP  343
 
 #ifdef HAVE_GETOPT_LONG
 static const struct option opts[] =  
@@ -300,6 +301,7 @@ static const struct myoption opts[] =
     { "dnssec-debug", 0, 0, LOPT_DNSSEC_DEBUG },
     { "dnssec-check-unsigned", 0, 0, LOPT_DNSSEC_CHECK },
     { "dnssec-no-timecheck", 0, 0, LOPT_DNSSEC_TIME },
+    { "dnssec-timestamp", 1, 0, LOPT_DNSSEC_STAMP },
 #ifdef OPTION6_PREFIX_CLASS 
     { "dhcp-prefix-class", 1, 0, LOPT_PREF_CLSS },
 #endif
@@ -463,6 +465,7 @@ static struct {
   { LOPT_DNSSEC_DEBUG, OPT_DNSSEC_DEBUG, NULL, gettext_noop("Disable upstream checking for DNSSEC debugging."), NULL },
   { LOPT_DNSSEC_CHECK, OPT_DNSSEC_NO_SIGN, NULL, gettext_noop("Ensure answers without DNSSEC are in unsigned zones."), NULL },
   { LOPT_DNSSEC_TIME, OPT_DNSSEC_TIME, NULL, gettext_noop("Don't check DNSSEC signature timestamps until first cache-reload"), NULL },
+  { LOPT_DNSSEC_STAMP, ARG_ONE, "<path>", gettext_noop("Timestamp file to verify system clock for DNSSEC"), NULL },
 #ifdef OPTION6_PREFIX_CLASS 
   { LOPT_PREF_CLSS, ARG_DUP, "set:tag,<class>", gettext_noop("Specify DHCPv6 prefix class"), NULL },
 #endif
@@ -3867,6 +3870,10 @@ static int one_opt(int option, char *arg, char *errstr, char *gen_err, int comma
       }
 
 #ifdef HAVE_DNSSEC
+    case LOPT_DNSSEC_STAMP:
+      daemon->timestamp_file = opt_string_alloc(arg); 
+      break;
+
     case LOPT_TRUST_ANCHOR:
       {
 	struct ds_config *new = opt_malloc(sizeof(struct ds_config));