add API to parse and extract IP from PTR name

Add an API to parse and extract either an IPv4 or IPv6 address from
a name using the reverse format. It takes care of family detection,
and returns a generic error in case of syntax error.

lib/dns/byaddr.c

@@ -15,8 +15,10 @@
 
 #include <stdbool.h>
 
+#include <isc/hex.h>
 #include <isc/mem.h>
 #include <isc/netaddr.h>
+#include <isc/parseint.h>
 #include <isc/result.h>
 #include <isc/string.h>
 #include <isc/util.h>
@@ -82,3 +84,118 @@ dns_byaddr_createptrname(const isc_netaddr_t *address, dns_name_t *name) {
 	isc_buffer_add(&buffer, len);
 	return dns_name_fromtext(name, &buffer, dns_rootname, 0);
 }
+
+static isc_result_t
+parseptrnamev4(const dns_name_t *name, isc_netaddr_t *addr) {
+	isc_buffer_t b;
+	static unsigned char inaddrarpa_data[] = "\007IN-ADDR\004ARPA";
+	static dns_name_t const inaddrarpa =
+		DNS_NAME_INITABSOLUTE(inaddrarpa_data);
+
+	if (!dns_name_issubdomain(name, &inaddrarpa)) {
+		return ISC_R_FAILURE;
+	}
+
+	*addr = (isc_netaddr_t){ .family = AF_INET };
+	isc_buffer_init(&b, &addr->type.in, sizeof(addr->type.in));
+
+	/*
+	 * Parse the IP address by extracting z y x w labels in reverse
+	 * order to put the IP blocks in the right order.
+	 */
+	for (int i = 3; i >= 0; i--) {
+		dns_label_t label;
+		char labelstr[4];
+		uint8_t block;
+
+		dns_name_getlabel(name, i, &label);
+		if (label.length > 4) {
+			return ISC_R_FAILURE;
+		}
+
+		/*
+		 * Skip the first byte of the label as it encodes the length
+		 * of the label (name wire format).
+		 */
+		strncpy(labelstr, (char *)label.base + 1, label.length);
+		labelstr[label.length - 1] = 0;
+		if (isc_parse_uint8(&block, labelstr, 10) != ISC_R_SUCCESS) {
+			return ISC_R_FAILURE;
+		}
+
+		isc_buffer_putuint8(&b, block);
+	}
+
+	INSIST(isc_buffer_availablelength(&b) == 0);
+	return ISC_R_SUCCESS;
+}
+
+static isc_result_t
+parseptrnamev6(const dns_name_t *name, isc_netaddr_t *addr) {
+	isc_buffer_t b;
+	isc_hex_decodectx_t ctx;
+	static unsigned char ip6arpa_data[] = "\003IP6\004ARPA";
+	static dns_name_t const ip6arpa = DNS_NAME_INITABSOLUTE(ip6arpa_data);
+
+	if (!dns_name_issubdomain(name, &ip6arpa)) {
+		return ISC_R_FAILURE;
+	}
+
+	*addr = (isc_netaddr_t){ .family = AF_INET6 };
+	isc_buffer_init(&b, &addr->type.in6, sizeof(addr->type.in6));
+	isc_hex_decodeinit(&ctx, isc_buffer_length(&b), &b);
+
+	/*
+	 * Parse the IP address by extracting labels in reverse order to
+	 * put the IP blocks in the right order.
+	 */
+	for (int i = 31; i >= 0; i--) {
+		dns_label_t label;
+
+		dns_name_getlabel(name, i, &label);
+		if (label.length != 2) {
+			return ISC_R_FAILURE;
+		}
+
+		/*
+		 * First byte is the label length
+		 */
+		if (isc_hex_decodechar(&ctx, label.base[1]) != ISC_R_SUCCESS) {
+			return ISC_R_FAILURE;
+		}
+	}
+
+	if (isc_hex_decodefinish(&ctx) != ISC_R_SUCCESS) {
+		return ISC_R_FAILURE;
+	}
+
+	INSIST(isc_buffer_availablelength(&b) == 0);
+	return ISC_R_SUCCESS;
+}
+
+isc_result_t
+dns_byaddr_parseptrname(const dns_name_t *name, isc_netaddr_t *addr) {
+	int result;
+
+	REQUIRE(DNS_NAME_VALID(name));
+	REQUIRE(addr != NULL);
+	REQUIRE(dns_name_isabsolute(name));
+
+	switch (dns_name_countlabels(name)) {
+	case 7:
+		/* z.y.x.w.in-addr.arpa. has 7 labels */
+		result = parseptrnamev4(name, addr);
+		break;
+	case 35:
+		/*
+		 * 0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0
+		 * .0.0.0.0.0.0.0.0.0.ip6.arpa. has 35 labels
+		 */
+		result = parseptrnamev6(name, addr);
+		break;
+	default:
+		result = ISC_R_FAILURE;
+	}
+
+	return result;
+}

lib/dns/include/dns/byaddr.h

@@ -52,3 +52,15 @@ dns_byaddr_createptrname(const isc_netaddr_t *address, dns_name_t *name);
  * \li	'address' is a valid address.
  * \li	'name' is a valid name with a dedicated buffer.
  */
+
+isc_result_t
+dns_byaddr_parseptrname(const dns_name_t *name, isc_netaddr_t *addr);
+/*%<
+ * Parse a name in a PTR format and convert it into a isc_net_addr_t. Support
+ * both IPv4 and IPv6 reverse format.
+ *
+ * Requires:
+ *
+ * \li	'name' is a valid name.
+ * \li  'addr' is a valid object
+ */

tests/dns/byaddr_test.c

@@ -0,0 +1,98 @@
+/*
+ * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+ *
+ * SPDX-License-Identifier: MPL-2.0
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, you can obtain one at https://mozilla.org/MPL/2.0/.
+ *
+ * See the COPYRIGHT file distributed with this work for additional
+ * information regarding copyright ownership.
+ */
+
+#include <sched.h> /* IWYU pragma: keep */
+#include <setjmp.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#define UNIT_TESTING
+#include <cmocka.h>
+
+#include <isc/lib.h>
+#include <isc/netaddr.h>
+
+#include <dns/byaddr.h>
+#include <dns/name.h>
+
+#include <tests/isc.h>
+
+ISC_RUN_TEST_IMPL(byaddr_parseptrname) {
+	struct {
+		const char *ptrname;
+		const char *address;
+	} tests[] = {
+		{ "1.0.168.192.in-addr.arpa.", "192.168.0.1" },
+		{ "ab.0.168.192.in-addr.arpa.", NULL },
+		{ "abcd.0.168.192.in-addr.arpa.", NULL },
+		{ "1111.0.168.192.in-addr.arpa.", NULL },
+		{ "1.0.168.192.in-addr.arp.", NULL },
+		{ "4.1.999.4.in-addr.arpa.", NULL },
+		{ "e.f.a.c.3.2.1.0.e.f.a.c.7.6.5.4.1.1.1.1.0.0.0.0.0.0.0."
+		  "0.1.2.e.f.ip6.arpa.",
+		  "fe21::1111:4567:cafe:123:cafe" },
+		{ "e.f.a.c.3.g.1.0.e.f.a.c.7.6.5.4.1.1.1.1.0.0.0.0.0.0.0."
+		  "0.1.2.e.f.ip6.arpa.",
+		  NULL },
+		{ "e.f.a.c.3.ee.1.0.e.f.a.c.7.6.5.4.1.1.1.1.0.0.0.0.0.0.0."
+		  "0.1.2.e.f.ip6.arpa.",
+		  NULL },
+		{ "e.f.a.c.3.2.1.0.e.f.a.c.7.6.5.4.1.1.1.1.0.0.0.0.0.0.0."
+		  "0.1.2.e.f.ip6.arp.",
+		  NULL },
+		{ "a::z.ip6.arpa.", NULL },
+		{ "ed.f.a.c.3.2.1.0.e.f.a.c.7.6.5.4.1.1.1.1.0.0.0.0.0.0.0."
+		  "0.1.2.e.f.ip6.arpa.",
+		  NULL },
+		{ "1.0. . "
+		  ".0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0."
+		  "ip6.arpa.",
+		  NULL },
+	};
+
+	for (size_t i = 0; i < ARRAY_SIZE(tests); i++) {
+		int result;
+		char bdata[128];
+		isc_buffer_t b;
+		isc_netaddr_t addr;
+		dns_name_t name;
+
+		isc_buffer_init(&b, bdata, sizeof(bdata));
+		dns_name_init(&name);
+		dns_name_setbuffer(&name, &b);
+		dns_name_fromstring(&name, tests[i].ptrname, NULL, 0, NULL);
+
+		result = dns_byaddr_parseptrname(&name, &addr);
+
+		if (tests[i].address) {
+			assert_int_equal(result, ISC_R_SUCCESS);
+		} else {
+			assert_int_not_equal(result, ISC_R_SUCCESS);
+		}
+
+		dns_name_invalidate(&name);
+		isc_buffer_clear(&b);
+		isc_netaddr_totext(&addr, &b);
+		isc_buffer_putuint8(&b, 0);
+
+		if (tests[i].address) {
+			result = strcmp(tests[i].address, b.base);
+			assert_int_equal(result, 0);
+		}
+	}
+}
+
+ISC_TEST_LIST_START
+ISC_TEST_ENTRY(byaddr_parseptrname)
+ISC_TEST_LIST_END
+ISC_TEST_MAIN

tests/dns/meson.build

@@ -12,6 +12,7 @@
 dns_tests = [
     'acl',
     'badcache',
+    'byaddr',
     'db',
     'dbdiff',
     'dbiterator',