base.c

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/*
 *   This library is free software; you can redistribute it and/or
 *   modify it under the terms of the GNU Lesser General Public
 *   License as published by the Free Software Foundation; either
 *   version 2.1 of the License, or (at your option) any later version.
 *
 *   This library is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 *   Lesser General Public License for more details.
 *
 *   You should have received a copy of the GNU Lesser General Public
 *   License along with this library; if not, write to the Free Software
 *   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 */
 
/**
 * $Id: 1d9e0d65a04823c67f7d2c294fa64b15a690dd2c $
 *
 * @file protocols/dns/base.c
 * @brief Functions to send/receive dns packets.
 *
 * @copyright 2008 The FreeRADIUS server project
 * @copyright 2021 Network RADIUS SAS (legal@networkradius.com)
 */
RCSID("$Id: 1d9e0d65a04823c67f7d2c294fa64b15a690dd2c $")
 
#include "dns.h"
#include "attrs.h"
#include <freeradius-devel/protocol/dns/rfc1034.h>
 
static uint32_t instance_count = 0;
static bool     instantiated = false;
 
typedef struct {
        uint16_t        code;
        uint16_t        length;
} dns_option_t;
 
fr_dict_t const *dict_dns;
 
static _Thread_local fr_dns_labels_t    fr_dns_labels;
static _Thread_local fr_dns_block_t     fr_dns_blocks[256];
static _Thread_local uint8_t            fr_dns_marker[65536];
 
extern fr_dict_autoload_t dns_dict[];
fr_dict_autoload_t dns_dict[] = {
        { .out = &dict_dns, .proto = "dns" },
        DICT_AUTOLOAD_TERMINATOR
};
 
fr_dict_attr_t const *attr_dns_packet;
fr_dict_attr_t const *attr_dns_question;
fr_dict_attr_t const *attr_dns_rr;
fr_dict_attr_t const *attr_dns_ns;
fr_dict_attr_t const *attr_dns_ar;
 
extern fr_dict_attr_autoload_t dns_dict_attr[];
fr_dict_attr_autoload_t dns_dict_attr[] = {
        { .out = &attr_dns_packet, .name = "Header", .type = FR_TYPE_STRUCT, .dict = &dict_dns },
        { .out = &attr_dns_question, .name = "Question", .type = FR_TYPE_STRUCT, .dict = &dict_dns },
        { .out = &attr_dns_rr, .name = "Resource-Record", .type = FR_TYPE_STRUCT, .dict = &dict_dns },
        { .out = &attr_dns_ns, .name = "Name-Server", .type = FR_TYPE_STRUCT, .dict = &dict_dns },
        { .out = &attr_dns_ar, .name = "Additional-Record", .type = FR_TYPE_STRUCT, .dict = &dict_dns },
        DICT_AUTOLOAD_TERMINATOR
};
 
 char const *fr_dns_packet_names[FR_DNS_CODE_MAX] = {
        [FR_DNS_QUERY] = "Query",
        [FR_DNS_INVERSE_QUERY] = "Inverse-Query",
        [FR_DNS_STATUS] = "Status",
        [FR_DNS_NOTIFY] = "Notify",
        [FR_DNS_UPDATE] = "Update",
        [FR_DNS_STATEFUL_OPERATION] = "Stateful-Operation",
};
 
FR_DICT_ATTR_FLAG_FUNC(fr_dns_attr_flags_t, dns_label)
FR_DICT_ATTR_FLAG_FUNC(fr_dns_attr_flags_t, dns_label_uncompressed)
 
static fr_dict_flag_parser_t const dns_flags[] = {
        { L("dns_label"),               { .func = dict_flag_dns_label } },
        { L("dns_label_uncompressed"),  { .func = dict_flag_dns_label_uncompressed } }
};
 
#define DECODE_FAIL(_reason) if (reason) *reason = FR_DNS_DECODE_FAIL_ ## _reason
 
static bool fr_dns_tlv_ok(uint8_t const *p, uint8_t const *end, fr_dns_decode_fail_t *reason)
{
        uint16_t len;
 
        while (p < end) {
                if ((p + 4) > end) {
                        DECODE_FAIL(MISSING_TLV_HEADER);
                        return false;
                }
 
                len = fr_nbo_to_uint16(p + 2);
                if ((p + 4 + len) > end) {
                        DECODE_FAIL(TLV_OVERFLOWS_RR);
                        return false;
                }
 
                p += 4 + len;
        }
 
        return true;
}
 
bool fr_dns_packet_ok(uint8_t const *packet, size_t packet_len, bool query, fr_dns_decode_fail_t *reason)
{
        uint8_t const *p, *end;
        int qdcount, count, expected;
        uint8_t opcode;
 
        if (packet_len <= DNS_HDR_LEN) {
                DECODE_FAIL(MIN_LENGTH_PACKET);
                return false;
        }
 
        if (packet_len > 65535) {
                DECODE_FAIL(MAX_LENGTH_PACKET);
                return false;
        }
 
        /*
         *      query=0, response=1
         */
        if (((packet[2] & 0x80) == 0) != query) {
                DECODE_FAIL(UNEXPECTED);
                return false;
        }
 
        /*
         *      @todo - the truncation rules mean that the various counts below are wrong, and the caller
         *      should retry over TCP.  This is really an indication to us, that we need to fully implement
         *      the truncation checks.
         */
        if ((packet[2] & 0x02) != 0) {
                DECODE_FAIL(TRUNCATED);
                return false;
        }
        qdcount = fr_nbo_to_uint16(packet + 4);
 
        opcode = (packet[2] >> 3) & 0x0f;
        if ((opcode >= FR_DNS_CODE_MAX) || !fr_dns_packet_names[opcode]) {
                DECODE_FAIL(UNKNOWN_OPCODE);
                return false;
        }
 
        /*
         *      RFC 2136 (DNS update) defines the four "count" fields to have different meanings:
         *
         *      ZOCOUNT The number of RRs in the Zone Section.
         *      PRCOUNT The number of RRs in the Prerequisite Section.
         *      UPCOUNT The number of RRs in the Update Section.
         *      ADCOUNT The number of RRs in the Additional Data Section.
         *
         *      @todo - we can likely do more validation checks on input packets.
         */
        if (query && (opcode != FR_OPCODE_VALUE_UPDATE)) {
                /*
                 *      There should be at least one query, and no
                 *      replies in the query.
                 *
                 *      @todo - unless it's an IQUERY, in which case
                 *      there should be no questions, and at least one
                 *      answer.
                 */
                if (!qdcount) {
                        DECODE_FAIL(NO_QUESTIONS);
                        return false;
                }
 
                if (fr_nbo_to_uint16(packet + 6) != 0) {
                        DECODE_FAIL(ANSWERS_IN_QUESTION);
                        return false;
                }
 
                if (fr_nbo_to_uint16(packet + 8) != 0) {
                        DECODE_FAIL(NS_IN_QUESTION);
                        return false;
                }
                // additional records can exist!
 
        } else {
                /*
                 *      Replies _usually_ copy the query.  But not
                 *      always And replies can have zero or more answers.
                 */
        }
 
        expected = fr_nbo_to_uint16(packet + 4) + fr_nbo_to_uint16(packet + 6) + fr_nbo_to_uint16(packet + 8) + fr_nbo_to_uint16(packet + 10);
        count = 0;
 
        p = packet + DNS_HDR_LEN;
        end = packet + packet_len;
 
        /*
         *      We track valid label targets in a simple array (up to
         *      2^14 bits of compressed pointer).
         *
         *      Note that some labels might appear in the RRDATA
         *      field, and we don't verify those here.  However, this
         *      function will verify the most common packets.  As a
         *      result, any issues with overflow, etc. are more
         *      difficult to exploit.
         */
        memset(fr_dns_marker, 0, packet_len < (1 << 14) ? packet_len : (1 << 14));
 
        /*
         *      Check for wildly fake packets, by making rough
         *      estimations.  This way we don't actually have to walk
         *      the packet.
         */
        if (p + (qdcount * 5) > end) {
                DECODE_FAIL(TOO_MANY_RRS);
                return false;
        }
        p += (qdcount * 5);
 
        if ((p + ((expected - qdcount) * (1 + 8 + 2))) > end) {
                DECODE_FAIL(TOO_MANY_RRS);
                return false;
        }
 
        /*
         *      The counts are at least vaguely OK, let's walk over the whole packet.
         */
        p = packet + DNS_HDR_LEN;
 
        /*
         *      Check that lengths of RRs match.
         */
        while (p < end) {
                uint16_t len = 0;
                uint8_t const *start = p;
                bool is_opt = false;
 
                /*
                 *      Simple DNS label decoder
                 *
                 *      @todo - move this to src/lib/util/dns.c,
                 *      perhaps as fr_dns_label_verify(), and then
                 *      have it also return a pointer to the next
                 *      label?  fr_dns_label_uncompressed_length()
                 *      does similar but slightly different things.
                 */
                while (p < end) {
                        /*
                         *      0x00 is "end of label"
                         */
                        if (!*p) {
                                p++;
                                break;
                        }
 
                        /*
                         *      2 octets of 14-bit pointer, which must
                         *      be at least somewhat sane.
                         */
                        if (*p >= 0xc0) {
                                ptrdiff_t offset;
 
                                if ((p + 2) > end) {
                                        DECODE_FAIL(POINTER_OVERFLOWS_PACKET);
                                        return false;
                                }
 
                                offset = p[1];
                                offset += ((*p & ~0xc0) << 8);
 
                                /*
                                 *      Can't point to the header.
                                 */
                                if (offset < 12) {
                                        DECODE_FAIL(POINTER_TO_HEADER);
                                        return false;
                                }
 
                                /*
                                 *      Can't point to the current label.
                                 */
                                if (offset >= (start - packet)) {
                                        DECODE_FAIL(POINTER_LOOPS);
                                        return false;
                                }
 
                                if (!fr_dns_marker[offset]) {
                                        DECODE_FAIL(POINTER_TO_NON_LABEL);
                                        return false;
                                }
 
                                /*
                                 *      A compressed pointer is the end of the current label.
                                 */
                                p += 2;
                                break;
                        }
 
                        /*
                         *      0b01 and 0b10 are forbidden
                         */
                        if (*p > 63) {
                                DECODE_FAIL(INVALID_POINTER);
                                return false;
                        }
 
                        /*
                         *      It must be a length byte, which doesn't cause overflow.
                         */
                        if ((p + *p + 1) > end) {
                                DECODE_FAIL(LABEL_OVERFLOWS_PACKET);
                                return false;
                        }
 
                        /*
                         *      Total length of labels can't be too high.
                         */
                        len += *p;
                        if (len >= 256) {
                                DECODE_FAIL(LABEL_TOO_LONG);
                                return false;
                        }
 
                        /*
                         *      Remember that this is where we have a
                         *      label.
                         */
                        fr_dns_marker[p - packet] = 1;
 
                        /*
                         *      Go to the next label.
                         */
                        p += *p + 1;
                }
 
                if (qdcount) {
                        /*
                         *      qtype + qclass
                         */
                        if ((p + 4) > end) {
                                DECODE_FAIL(MISSING_QD_HEADER);
                                return false;
                        }
 
                        p += 4;
                        qdcount--;
                        goto next;
                }
 
                /*
                 *      type (2) + class (2) + TTL (4)
                 *
                 *      These are overloaded for the OPT RR
                 *      and possibly others, but the basic
                 *      idea is the same.
                 */
                if ((p + 8) > end) {
                        DECODE_FAIL(MISSING_RR_HEADER);
                        return false;
                }
                is_opt = (p[0] == 0) && (p[1] == 41);
                p += 8;
 
                /*
                 *      rr_len
                 */
                if ((p + 2) > end) {
                        DECODE_FAIL(MISSING_RR_LEN);
                        return false;
                }
 
                /*
                 *      @todo - RFC2136 allows RDLENGTH=0 for many cases.
                 */
                len = fr_nbo_to_uint16(p);
                if (!is_opt && (len == 0)) {
                        DECODE_FAIL(ZERO_RR_LEN);
                        return false;
                }
 
                p += 2;
                if ((p + len) > end) {
                        DECODE_FAIL(RR_OVERFLOWS_PACKET);
                        return false;
                }
 
                /*
                 *      Verify the TLVs, too.
                 */
                if (is_opt && !fr_dns_tlv_ok(p, p + len, reason)) {
                        return false;
                }
 
                p += len;
 
next:
                count++;
 
                if (count > expected) {
                        DECODE_FAIL(TOO_MANY_RRS);
                        return false;
                }
        }
 
        if (count != expected) {
                DECODE_FAIL(TOO_FEW_RRS);
                return false;
        }
 
        /*
         *      @todo - save fr_dns_marker[] data, so that it can be used by fr_dns_labels_get().  This helps
         *      to reduce redundant work.
         */
 
        DECODE_FAIL(NONE);
        return true;
}
 
fr_dns_labels_t *fr_dns_labels_get(uint8_t const *packet, size_t packet_len, bool init_mark)
{
        fr_dns_labels_t *lb = &fr_dns_labels;
 
        lb->max = 256;
        lb->mark = fr_dns_marker;
        lb->blocks = fr_dns_blocks;
 
        lb->start = packet;
        lb->end = packet + packet_len;
 
        lb->num = 1;
        lb->blocks[0].start = DNS_HDR_LEN;
        lb->blocks[0].end = DNS_HDR_LEN;
 
        if (init_mark) {
                fr_assert(packet_len <= 65535);
                memset(lb->mark, 0, packet_len);
        }
 
        return lb;
}
 
/** Resolve/cache attributes in the DNS dictionary
 *
 * @return
 *      - 0 on success.
 *      - -1 on failure.
 */
int fr_dns_global_init(void)
{
        if (instance_count > 0) {
                instance_count++;
                return 0;
        }
 
        instance_count++;
 
        if (fr_dict_autoload(dns_dict) < 0) {
        fail:
                instance_count--;
                return -1;
        }
        if (fr_dict_attr_autoload(dns_dict_attr) < 0) {
                fr_dict_autofree(dns_dict);
                goto fail;
        }
 
        instantiated = true;
        return 0;
}
 
void fr_dns_global_free(void)
{
        if (!instantiated) return;
 
        fr_assert(instance_count > 0);
 
        if (--instance_count > 0) return;
 
        fr_dict_autofree(dns_dict);
        instantiated = false;
}
 
static bool attr_valid(fr_dict_attr_t *da)
{
        if (da->flags.array) {
                fr_strerror_const("The 'array' flag cannot be used with DNS");
                return false;
        }
 
        if (da->type == FR_TYPE_ATTR) {
                fr_strerror_const("The 'attribute' data type cannot be used with DNS");
                return false;
        }
 
        if (fr_dns_flag_dns_label_any(da)) {
                if (da->type != FR_TYPE_STRING) {
                        fr_strerror_const("The 'dns_label' flag can only be used with attributes of type 'string'");
                        return false;
                }
                da->flags.is_known_width = true;        /* Lie so we don't trip up the main validation checks */
        }
 
        switch (da->type) {
        case FR_TYPE_IP:
                da->flags.is_known_width = true;
                break;
 
        default:
                break;
        }
 
        return true;
}
 
extern fr_dict_protocol_t libfreeradius_dns_dict_protocol;
fr_dict_protocol_t libfreeradius_dns_dict_protocol = {
        .name = "dns",
        .default_type_size = 2,
        .default_type_length = 2,
        .attr = {
                .flags = {
                        .table = dns_flags,
                        .table_len = NUM_ELEMENTS(dns_flags),
                        .len = sizeof(fr_dns_attr_flags_t)
                },
                .valid = attr_valid
        },
 
        .init = fr_dns_global_init,
        .free = fr_dns_global_free,
};