Add --filter and --filter-AAAA options.

CHANGELOG

@@ -8,7 +8,10 @@ version 2.87
 	Add --nftset option, like --ipset but for the newer nftables.
 	Thanks to Chen Zhenge for the patch.
 	
-	
+	Add --filter-A and --filter-AAAA options, to remove IPv4 or IPv6
+	addresses from DNS answers.
+
+
 version 2.86
 	Handle DHCPREBIND requests in the DHCPv6 server code.
 	Thanks to Aichun Li for spotting this omission, and the initial

man/dnsmasq.8

@@ -348,6 +348,12 @@ the public DNS and can cause problems by triggering dial-on-demand links. This f
 to filter such requests. The requests blocked are for records of types SOA and SRV, and type ANY where the 
 requested name has underscores, to catch LDAP requests.
 .TP
+.B --filter-A
+Remove A records from answers. No IPv4 addresses will be returned.
+.TP
+.B --filter-AAAA
+Remove AAAA records from answers. No IPv6 addresses will be returned.
+.TP
 .B \-r, --resolv-file=<file>
 Read the IP addresses of the upstream nameservers from <file>, instead of
 /etc/resolv.conf. For the format of this file see

src/dnsmasq.h

@@ -275,7 +275,9 @@ struct event_desc {
 #define OPT_UMBRELLA_DEVID 64
 #define OPT_CMARK_ALST_EN  65
 #define OPT_QUIET_TFTP     66
-#define OPT_LAST           67
+#define OPT_FILTER_A       67
+#define OPT_FILTER_AAAA    68
+#define OPT_LAST           69
 
 #define OPTION_BITS (sizeof(unsigned int)*8)
 #define OPTION_SIZE ( (OPT_LAST/OPTION_BITS)+((OPT_LAST%OPTION_BITS)!=0) )
@@ -1749,7 +1751,11 @@ int do_poll(int timeout);
 size_t rrfilter(struct dns_header *header, size_t plen, int mode);
 u16 *rrfilter_desc(int type);
 int expand_workspace(unsigned char ***wkspc, int *szp, int new);
-
+/* modes. */
+#define RRFILTER_EDNS0   0
+#define RRFILTER_DNSSEC  1
+#define RRFILTER_A       2
+#define RRFILTER_AAAA    3
 /* edns0.c */
 unsigned char *find_pseudoheader(struct dns_header *header, size_t plen,
 				   size_t *len, unsigned char **p, int *is_sign, int *is_last);

src/edns0.c

@@ -178,7 +178,7 @@ size_t add_pseudoheader(struct dns_header *header, size_t plen, unsigned char *l
 	    memcpy(buff, datap, rdlen);	      
 	  
 	  /* now, delete OPT RR */
-	  plen = rrfilter(header, plen, 0);
+	  plen = rrfilter(header, plen, RRFILTER_EDNS0);
 	  
 	  /* Now, force addition of a new one */
 	  p = NULL;	  

src/forward.c

@@ -629,7 +629,7 @@ static size_t process_reply(struct dns_header *header, time_t now, struct server
 	  if (added_pheader)
 	    {
 	      /* client didn't send EDNS0, we added one, strip it off before returning answer. */
-	      n = rrfilter(header, n, 0);
+	      n = rrfilter(header, n, RRFILTER_EDNS0);
 	      pheader = NULL;
 	    }
 	  else
@@ -718,7 +718,17 @@ static size_t process_reply(struct dns_header *header, time_t now, struct server
 	      cache_secure = 0;
 	    }
 	}
-      
+
+      /* Before extract_addresses() */
+      if (rcode == NOERROR)
+	{
+	  if (option_bool(OPT_FILTER_A))
+	    n = rrfilter(header, n, RRFILTER_A);
+
+	  if (option_bool(OPT_FILTER_AAAA))
+	    n = rrfilter(header, n, RRFILTER_AAAA);
+	}
+
       if (extract_addresses(header, n, daemon->namebuff, now, ipsets, nftsets, is_sign, check_rebind, no_cache, cache_secure, &doctored))
 	{
 	  my_syslog(LOG_WARNING, _("possible DNS-rebind attack detected: %s"), daemon->namebuff);
@@ -748,7 +758,7 @@ static size_t process_reply(struct dns_header *header, time_t now, struct server
       
       /* If the requestor didn't set the DO bit, don't return DNSSEC info. */
       if (!do_bit)
-	n = rrfilter(header, n, 1);
+	n = rrfilter(header, n, RRFILTER_DNSSEC);
     }
 #endif
 
@@ -772,7 +782,7 @@ static size_t process_reply(struct dns_header *header, time_t now, struct server
       u16 swap = htons((u16)ede);
       n = add_pseudoheader(header, n, limit, daemon->edns_pktsz, EDNS0_OPTION_EDE, (unsigned char *)&swap, 2, do_bit, 1);
     }
-  
+
   return n;
 }
 

src/option.c

@@ -175,7 +175,9 @@ struct myoption {
 #define LOPT_CMARK_ALST    366
 #define LOPT_QUIET_TFTP    367
 #define LOPT_NFTSET        368
- 
+#define LOPT_FILTER_A      369
+#define LOPT_FILTER_AAAA   370
+
 #ifdef HAVE_GETOPT_LONG
 static const struct option opts[] =  
 #else
@@ -212,6 +214,8 @@ static const struct myoption opts[] =
     { "ignore-address", 1, 0, LOPT_IGNORE_ADDR },
     { "selfmx", 0, 0, 'e' },
     { "filterwin2k", 0, 0, 'f' },
+    { "filter-A", 0, 0, LOPT_FILTER_A },
+    { "filter-AAAA", 0, 0, LOPT_FILTER_AAAA },
     { "pid-file", 2, 0, 'x' },
     { "strict-order", 0, 0, 'o' },
     { "server", 1, 0, 'S' },
@@ -382,6 +386,8 @@ static struct {
   { 'e', OPT_SELFMX, NULL, gettext_noop("Return self-pointing MX records for local hosts."), NULL },
   { 'E', OPT_EXPAND, NULL, gettext_noop("Expand simple names in /etc/hosts with domain-suffix."), NULL },
   { 'f', OPT_FILTER, NULL, gettext_noop("Don't forward spurious DNS requests from Windows hosts."), NULL },
+  { LOPT_FILTER_A, OPT_FILTER_A, NULL, gettext_noop("Don't include IPv4 addresses in DNS answers."), NULL },
+  { LOPT_FILTER_AAAA, OPT_FILTER_AAAA, NULL, gettext_noop("Don't include IPv6 addresses in DNS answers."), NULL },
   { 'F', ARG_DUP, "<ipaddr>,...", gettext_noop("Enable DHCP in the range given with lease duration."), NULL },
   { 'g', ARG_ONE, "<groupname>", gettext_noop("Change to this group after startup (defaults to %s)."), CHGRP },
   { 'G', ARG_DUP, "<hostspec>", gettext_noop("Set address or hostname for a specified machine."), NULL },

src/rrfilter.c

@@ -156,7 +156,7 @@ static int check_rrs(unsigned char *p, struct dns_header *header, size_t plen, i
 }
 	
 
-/* mode is 0 to remove EDNS0, 1 to filter DNSSEC RRs */
+/* mode may be remove EDNS0 or DNSSEC RRs or remove A or AAAA from answer section. */
 size_t rrfilter(struct dns_header *header, size_t plen, int mode)
 {
   static unsigned char **rrs;
@@ -192,20 +192,37 @@ size_t rrfilter(struct dns_header *header, size_t plen, int mode)
       if (!ADD_RDLEN(header, p, plen, rdlen))
 	return plen;
 
-      /* Don't remove the answer. */
-      if (i < ntohs(header->ancount) && type == qtype && class == qclass)
-	continue;
-      
-      if (mode == 0) /* EDNS */
+      if (mode == RRFILTER_EDNS0) /* EDNS */
 	{
 	  /* EDNS mode, remove T_OPT from additional section only */
 	  if (i < (ntohs(header->nscount) + ntohs(header->ancount)) || type != T_OPT)
 	    continue;
 	}
-      else if (type != T_NSEC && type != T_NSEC3 && type != T_RRSIG)
-	/* DNSSEC mode, remove SIGs and NSECs from all three sections. */
-	continue;
-      
+      else if (mode == RRFILTER_DNSSEC)
+	{
+	  if (type != T_NSEC && type != T_NSEC3 && type != T_RRSIG)
+	    /* DNSSEC mode, remove SIGs and NSECs from all three sections. */
+	    continue;
+
+	  /* Don't remove the answer. */
+	  if (i < ntohs(header->ancount) && type == qtype && class == qclass)
+	    continue;
+	}
+      else
+	{
+	  /* Only looking at answer section now. */
+	  if (i >= ntohs(header->ancount))
+	    break;
+
+	  if (class != C_IN)
+	    continue;
+	  
+	  if (mode == RRFILTER_A && type != T_A)
+	    continue;
+
+	  if (mode == RRFILTER_AAAA && type != T_AAAA)
+	    continue;
+	}
       
       if (!expand_workspace(&rrs, &rr_sz, rr_found + 1))
 	return plen;