[Dnsmasq-discuss] Patch with option to filter A records

Trey Sis treysis at gmx.net
Wed Jun 9 12:13:34 UTC 2021


Dropping the patch file as attachment.

On 6/5/2021 18:20, Trey Sis wrote:
> For some reason I didn't receive all mails from the list in my inbox, so
> I'll reply to this mail. Also sorry if I mess something up. I haven't
> used a mailing list in over two decades.
>
> On 6/5/2021 17:37, Geert Stappers via Dnsmasq-discuss wrote:
>> On Sat, Jun 05, 2021 at 03:34:59PM +0200, Trey Sis wrote:
>>> Is there any chance for such a patch to make it into official
>>> dnsmasq? Are pull-requests on github acted on? That would be my
>>> preferred method, otherwise I will post the patch here.
>>>
>>> Cheers,
>>> Treysis
>>>
>>> Patch:
>>>
>>> >From bd22a36f76e35a0dc6c8be8996056318fec96e5e Mon Sep 17 00:00:00 2001
>>> From: treysis <treysis at gmx.net>
>>> Date: Sat, 5 Jun 2021 15:27:26 +0200
>>> Subject: [PATCH] Add option to filter A record requests
>>>
>>> ---
>>>   src/dnsmasq.h |  3 ++-
>>>   src/option.c  |  3 +++
>>>   src/rfc1035.c | 11 +++++++++++
>>>   3 files changed, 16 insertions(+), 1 deletion(-)
>>>
>> That patch did not apply cleanly. With some manual work it did apply.
>> Except to see the reworked version here soon.
>> Hopefully is Author left intact. (I'm about to `git send-email` a patch
>> that is not mine ).
>> And the original patch lacks update of the manual page,
>> it is where I chip in.
>>
>>
>> Cheers
>> Geert Stappers
>>
>> P.S.
>> https://git-send-email.io/ for instructions on email patches.
>> See "Linux kernel development all over the place" in it.
>
> Thanks for the tip. I'll have a look at that for future use. The patch
> probably didn't apply because I just copy&pasted it here. The source
> code is a bit inconsistent in using a mix of spaces and tabs for
> indentation. Tabs probably got lost when copying.
>
> Thanks also for taking care of the manpage! Happy to see this hopefully
> land in upstream :)
>
> Cheers,
>
> Treysis
>
>
>
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> Dnsmasq-discuss at lists.thekelleys.org.uk
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-------------- next part --------------
From 57c7fcb0b3caccae7376f71ab1a9ae74f0e7f6d9 Mon Sep 17 00:00:00 2001
From: treysis <treysis at gmx.net>
Date: Sat, 5 Jun 2021 15:27:26 +0200
Subject: [PATCH] Add option to filter A record requests

---
 src/dnsmasq.h |  3 ++-
 src/option.c  |  3 +++
 src/rfc1035.c | 11 +++++++++++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/src/dnsmasq.h b/src/dnsmasq.h
index b27737b..2fec7d1 100644
--- a/src/dnsmasq.h
+++ b/src/dnsmasq.h
@@ -272,7 +272,8 @@ struct event_desc {
 #define OPT_LOG_DEBUG      62
 #define OPT_UMBRELLA       63
 #define OPT_UMBRELLA_DEVID 64
-#define OPT_LAST           65
+#define OPT_FILTER_A       65
+#define OPT_LAST           66
 
 #define OPTION_BITS (sizeof(unsigned int)*8)
 #define OPTION_SIZE ( (OPT_LAST/OPTION_BITS)+((OPT_LAST%OPTION_BITS)!=0) )
diff --git a/src/option.c b/src/option.c
index cacfaa6..43dc3cb 100644
--- a/src/option.c
+++ b/src/option.c
@@ -171,6 +171,7 @@ struct myoption {
 #define LOPT_DYNHOST       362
 #define LOPT_LOG_DEBUG     363
 #define LOPT_UMBRELLA	   364
+#define LOPT_FILTER_A      365
  
 #ifdef HAVE_GETOPT_LONG
 static const struct option opts[] =  
@@ -347,6 +348,7 @@ static const struct myoption opts[] =
     { "dynamic-host", 1, 0, LOPT_DYNHOST },
     { "log-debug", 0, 0, LOPT_LOG_DEBUG },
 	{ "umbrella", 2, 0, LOPT_UMBRELLA },
+    { "filter-a", 0, 0, LOPT_FILTER_A },
     { NULL, 0, 0, 0 }
   };
 
@@ -530,6 +532,7 @@ static struct {
   { LOPT_DUMPMASK, ARG_ONE, "<hex>", gettext_noop("Mask which packets to dump"), NULL },
   { LOPT_SCRIPT_TIME, OPT_LEASE_RENEW, NULL, gettext_noop("Call dhcp-script when lease expiry changes."), NULL },
   { LOPT_UMBRELLA, ARG_ONE, "[=<optspec>]", gettext_noop("Send Cisco Umbrella identifiers including remote IP."), NULL },
+  { LOPT_FILTER_A, OPT_FILTER_A, NULL, gettext_noop("Filter all A requests."), NULL },
   { 0, 0, NULL, NULL, NULL }
 }; 
 
diff --git a/src/rfc1035.c b/src/rfc1035.c
index 9bc5ef2..1043773 100644
--- a/src/rfc1035.c
+++ b/src/rfc1035.c
@@ -1843,6 +1843,17 @@ size_t answer_request(struct dns_header *header, char *limit, size_t qlen,
 	    }
 	}
 
+	/* filter A forwards */
+	if (qtype == T_A && option_bool(OPT_FILTER_A))
+	  {
+	    /* return a null reply */
+		ans = 1;
+		if (!dryrun) 
+		  log_query(F_CONFIG | F_IPV6 | F_NEG, name, &addr, NULL);
+		break;
+	  }
+	/* end of filtering A */
+
       if (!ans)
 	return 0; /* failed to answer a question */
     }


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