decode.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: d237a297b9036bf56777e165200f58bea9ba0112 $
 *
 * @file protocols/dns/decode.c
 * @brief Functions to decode DNS packets.
 *
 * @author Alan DeKok (aland@freeradius.org)
 *
 * @copyright 2021 The FreeRADIUS server project
 * @copyright 2021 NetworkRADIUS SARL (legal@networkradius.com)
 */
#include <freeradius-devel/io/test_point.h>
#include <freeradius-devel/util/dns.h>
#include <freeradius-devel/util/proto.h>
#include <freeradius-devel/util/struct.h>
 
#include "dns.h"
#include "attrs.h"
 
static ssize_t decode_option(TALLOC_CTX *ctx, fr_pair_list_t *out,
                              fr_dict_attr_t const *parent,
                              uint8_t const *data, size_t const data_len, void *decode_ctx);
 
static ssize_t decode_value(TALLOC_CTX *ctx, fr_pair_list_t *out,
                            fr_dict_attr_t const *parent,
                            uint8_t const *data, size_t const data_len, void *decode_ctx);
 
static ssize_t decode_tlv_trampoline(TALLOC_CTX *ctx, fr_pair_list_t *out,
                                     fr_dict_attr_t const *parent,
                                     uint8_t const *data, size_t const data_len, void *decode_ctx)
{
        return fr_pair_tlvs_from_network(ctx, out, parent, data, data_len, decode_ctx, decode_option, NULL, true);
}
 
 
static ssize_t decode_value_trampoline(TALLOC_CTX *ctx, fr_pair_list_t *out,
                                       fr_dict_attr_t const *parent,
                                       uint8_t const *data, size_t const data_len, void *decode_ctx)
{
        if ((parent->type == FR_TYPE_STRING) && fr_dns_flag_dns_label(parent)) {
                fr_dns_ctx_t            *packet_ctx = decode_ctx;
 
                return fr_pair_dns_labels_from_network(ctx, out, parent, packet_ctx->packet, data, data_len, packet_ctx->lb, false);
        }
 
        return decode_value(ctx, out, parent, data, data_len, decode_ctx);
}
 
 
static ssize_t decode_value(TALLOC_CTX *ctx, fr_pair_list_t *out,
                            fr_dict_attr_t const *parent,
                            uint8_t const *data, size_t const data_len, void *decode_ctx)
{
        ssize_t                 slen;
        fr_pair_t               *vp;
        uint8_t                 prefix_len;
 
        FR_PROTO_HEX_DUMP(data, data_len, "decode_value");
 
        switch (parent->type) {
        /*
         *      Address MAY be shorter than 16 bytes.
         */
        case FR_TYPE_IPV6_PREFIX:
                if ((data_len == 0) || (data_len > (1 + sizeof(vp->vp_ipv6addr)))) {
                raw:
                        return fr_pair_raw_from_network(ctx, out, parent, data, data_len);
 
                }
 
                /*
                 *      Structs used fixed length fields
                 */
                if (parent->parent->type == FR_TYPE_STRUCT) {
                        if (data_len != (1 + sizeof(vp->vp_ipv6addr))) goto raw;
 
                        vp = fr_pair_afrom_da(ctx, parent);
                        if (!vp) return PAIR_DECODE_OOM;
 
                        vp->vp_ip.af = AF_INET6;
                        vp->vp_ip.prefix = data[0];
                        memcpy(&vp->vp_ipv6addr, data + 1, data_len - 1);
                        break;
                }
 
                /*
                 *      No address, the prefix length MUST be zero.
                 */
                if (data_len == 1) {
                        if (data[0] != 0) goto raw;
 
                        vp = fr_pair_afrom_da(ctx, parent);
                        if (!vp) return PAIR_DECODE_OOM;
 
                        vp->vp_ip.af = AF_INET6;
                        break;
                }
 
                prefix_len = data[0];
 
                /*
                 *      If we have a /64 prefix but only 7 bytes of
                 *      address, that's an error.
                 */
                if (fr_bytes_from_bits(prefix_len) > (data_len - 1)) goto raw;
 
                vp = fr_pair_afrom_da(ctx, parent);
                if (!vp) return PAIR_DECODE_OOM;
 
                vp->vp_ip.af = AF_INET6;
                vp->vp_ip.prefix = prefix_len;
                memcpy(&vp->vp_ipv6addr, data + 1, data_len - 1);
                break;
 
        /*
         *      A bool is encoded as an empty option if it's
         *      true.  A bool is omitted entirely if it's
         *      false.
         */
        case FR_TYPE_BOOL:
                if (data_len != 0) goto raw;
                vp = fr_pair_afrom_da(ctx, parent);
                if (!vp) return PAIR_DECODE_OOM;
                vp->vp_bool = true;
                break;
 
        case FR_TYPE_STRUCT:
                slen = fr_struct_from_network(ctx, out, parent, data, data_len,
                                              decode_ctx, decode_value_trampoline, NULL);
                if (slen < 0) return slen;
                return data_len;
 
        case FR_TYPE_GROUP:
                return PAIR_DECODE_FATAL_ERROR; /* not supported */
 
        default:
                vp = fr_pair_afrom_da(ctx, parent);
                if (!vp) return PAIR_DECODE_OOM;
 
                if (fr_value_box_from_network(vp, &vp->data, vp->vp_type, vp->da,
                                              &FR_DBUFF_TMP(data, data_len), data_len, true) < 0) {
                        FR_PROTO_TRACE("failed decoding?");
                        talloc_free(vp);
                        goto raw;
                }
                break;
        }
 
        vp->vp_tainted = true;
        fr_pair_append(out, vp);
        return data_len;
}
 
 
#define DNS_GET_OPTION_NUM(_x)  fr_nbo_to_uint16(_x)
#define DNS_GET_OPTION_LEN(_x)  fr_nbo_to_uint16((_x) + 2)
 
static ssize_t decode_option(TALLOC_CTX *ctx, fr_pair_list_t *out,
                              fr_dict_attr_t const *parent,
                              uint8_t const *data, size_t const data_len, void *decode_ctx)
{
        unsigned int            option;
        size_t                  len;
        ssize_t                 slen;
        fr_dict_attr_t const    *da;
        fr_dns_ctx_t            *packet_ctx = decode_ctx;
 
#ifdef STATIC_ANALYZER
        if (!packet_ctx || !packet_ctx->tmp_ctx) return PAIR_DECODE_FATAL_ERROR;
#endif
 
        /*
         *      Must have at least an option header.
         */
        if (data_len < 4) {
                fr_strerror_printf("%s: Insufficient data", __FUNCTION__);
                return -(data_len);
        }
 
        option = DNS_GET_OPTION_NUM(data);
        len = DNS_GET_OPTION_LEN(data);
        if (len > (data_len - 4)) {
                fr_strerror_printf("%s: Option overflows input.  "
                                   "Optional length must be less than %zu bytes, got %zu bytes",
                                   __FUNCTION__, data_len - 4, len);
                return PAIR_DECODE_FATAL_ERROR;
        }
 
        FR_PROTO_HEX_DUMP(data, len + 4, "decode_option");
 
        da = fr_dict_attr_child_by_num(parent, option);
        if (!da) {
                da = fr_dict_attr_unknown_raw_afrom_num(packet_ctx->tmp_ctx, parent, option);
                if (!da) return PAIR_DECODE_FATAL_ERROR;
        }
        FR_PROTO_TRACE("decode context changed %s -> %s",da->parent->name, da->name);
 
        if ((da->type == FR_TYPE_STRING) && fr_dns_flag_dns_label(da)) {
                slen = fr_pair_dns_labels_from_network(ctx, out, da, packet_ctx->packet, data + 4, len, packet_ctx->lb, true);
 
        } else if (da->flags.array) {
                slen = fr_pair_array_from_network(ctx, out, da, data + 4, len, decode_ctx, decode_value);
 
        } else {
                slen = decode_value(ctx, out, da, data + 4, len, decode_ctx);
        }
        fr_dict_attr_unknown_free(&da);
 
        if (slen < 0) return slen;
 
        return len + 4;
}
 
static ssize_t decode_record(TALLOC_CTX *ctx, fr_pair_list_t *out, fr_dict_attr_t const *attr,
                             uint8_t const *rr, uint8_t const *end,
                             fr_dns_ctx_t *packet_ctx, uint8_t const *counter)
{
        unsigned int i, count;
        uint8_t const *p = rr;
 
        /*
         *      The header has a count of how many records we need to decode.
         */
        count = fr_nbo_to_uint16(counter);
        FR_PROTO_TRACE("Decoding %u of %s", count, attr->name);
 
        /* coverity[tainted_data] */
        for (i = 0; (i < count) && (p < end); i++) {
                ssize_t slen;
 
                FR_PROTO_HEX_DUMP(p, end - p, "fr_dns_decode - %s %u/%u", attr->name, i, count);
 
                slen = fr_struct_from_network(ctx, out, attr, p, end - p,
                                              packet_ctx, decode_value_trampoline, decode_tlv_trampoline);
                if (slen < 0) return slen;
                if (!slen) break;
 
                fr_assert(slen <= (end - p));
 
                p += slen;
        }
 
        return p - rr;
}
 
/** Decode a DNS packet
 *
 */
ssize_t fr_dns_decode(TALLOC_CTX *ctx, fr_pair_list_t *out, uint8_t const *packet, size_t packet_len, fr_dns_ctx_t *packet_ctx)
{
        ssize_t                 slen;
        uint8_t const           *p, *end;
 
        if (packet_len < DNS_HDR_LEN) return 0;
 
        /*
         *      @todo - synthesize Packet-Type from the various fields.
         */
 
        FR_PROTO_HEX_DUMP(packet, packet_len, "fr_dns_decode");
 
        /*
         *      Decode the header.
         */
        slen = fr_struct_from_network(ctx, out, attr_dns_packet, packet, DNS_HDR_LEN,
                                      packet_ctx, decode_value_trampoline, NULL); /* no TLVs in the header */
        if (slen < 0) {
                fr_strerror_printf("Failed decoding DNS header - %s", fr_strerror());
                return slen;
        }
        fr_assert(slen == DNS_HDR_LEN);
 
        p = packet + DNS_HDR_LEN;
        end = packet + packet_len;
        FR_PROTO_HEX_DUMP(p, end - p, "fr_dns_decode - after header");
 
        slen = decode_record(ctx, out, attr_dns_question, p, end, packet_ctx, packet + 4);
        if (slen < 0) {
                fr_strerror_printf("Failed decoding questions - %s", fr_strerror());
                return slen;
        }
        p += slen;
        FR_PROTO_HEX_DUMP(p, end - p, "fr_dns_decode - after %zd bytes of questions", slen);
 
        slen = decode_record(ctx, out, attr_dns_rr, p, end, packet_ctx, packet + 6);
        if (slen < 0) {
                fr_strerror_printf("Failed decoding RRs - %s", fr_strerror());
                return slen - (p - packet);
        }
        p += slen;
        FR_PROTO_HEX_DUMP(p, end - p, "fr_dns_decode - after %zd bytes of RRs", slen);
 
        slen = decode_record(ctx, out, attr_dns_ns, p, end, packet_ctx, packet + 8);
        if (slen < 0) {
                fr_strerror_printf("Failed decoding NS - %s", fr_strerror());
                return slen - (p - packet);
        }
        p += slen;
        FR_PROTO_HEX_DUMP(p, end - p, "fr_dns_decode - after %zd bytes of NS", slen);
 
        slen = decode_record(ctx, out, attr_dns_ar, p, end, packet_ctx, packet + 10);
        if (slen < 0) {
                fr_strerror_printf("Failed decoding additional records - %s", fr_strerror());
                return slen - (p - packet);
        }
        FR_PROTO_HEX_DUMP(p, end - p, "fr_dns_decode - after %zd bytes of additional records", slen);
 
//      p += slen;
 
        return packet_len;
}
 
/** Decode DNS RR
 *
 * @param[in] ctx context       to alloc new attributes in.
 * @param[in,out] out           Where to write the decoded options.
 * @param[in] parent            to lookup attributes in.
 * @param[in] data              to parse.
 * @param[in] data_len          of data to parse.
 * @param[in] decode_ctx        Unused.
 */
static ssize_t decode_rr(TALLOC_CTX *ctx, fr_pair_list_t *out, UNUSED fr_dict_attr_t const *parent,
                         uint8_t const *data, size_t data_len, void *decode_ctx)
{
        ssize_t                 slen;
        fr_dns_ctx_t    *packet_ctx = (fr_dns_ctx_t *) decode_ctx;
 
        FR_PROTO_TRACE("%s called to parse %zu byte(s)", __FUNCTION__, data_len);
 
        if (data_len == 0) return 0;
 
        /*
         *      This function is only used for testing, so update decode_ctx
         */
        packet_ctx->packet = data;
        packet_ctx->packet_len = data_len;
 
        FR_PROTO_HEX_DUMP(data, data_len, NULL);
 
        /*
         *      There should be at least room for the RR header
         */
        if (data_len < 9) {
                fr_strerror_printf("%s: Insufficient data", __FUNCTION__);
                return -1;
        }
 
        slen = fr_struct_from_network(ctx, out, attr_dns_rr, data, data_len,
                                      decode_ctx, decode_value_trampoline, decode_tlv_trampoline);
        if (slen < 0) return slen;
 
        FR_PROTO_TRACE("decoding option complete, returning %zd byte(s)", slen);
        return slen;
}
 
/*
 *      Test points
 */
static int decode_test_ctx(void **out, TALLOC_CTX *ctx, UNUSED fr_dict_t const *dict)
{
        fr_dns_ctx_t *test_ctx;
 
        test_ctx = talloc_zero(ctx, fr_dns_ctx_t);
 
        test_ctx->tmp_ctx = talloc(test_ctx, uint8_t);
        *out = test_ctx;
 
        return 0;
}
 
fr_table_num_ordered_t fr_dns_reason_fail_table[] = {
        { L("none"),                                            FR_DNS_DECODE_FAIL_NONE         },
        { L("packet is smaller than DNS header"),               FR_DNS_DECODE_FAIL_MIN_LENGTH_PACKET    },
        { L("packet is larger than 65535"),                     FR_DNS_DECODE_FAIL_MAX_LENGTH_PACKET    },
        { L("expected query / answer, got answer / query"),     FR_DNS_DECODE_FAIL_UNEXPECTED           },
        { L("no 'questions' in query packet"),                  FR_DNS_DECODE_FAIL_NO_QUESTIONS },
        { L("unexprected answers in query packet"),             FR_DNS_DECODE_FAIL_ANSWERS_IN_QUESTION  },
        { L("unexpected NS records in query packet"),           FR_DNS_DECODE_FAIL_NS_IN_QUESTION       },
        { L("invalid label for resource record"),               FR_DNS_DECODE_FAIL_INVALID_RR_LABEL     },
        { L("missing resource record header"),                  FR_DNS_DECODE_FAIL_MISSING_RR_HEADER    },
        { L("missing resource record length field"),            FR_DNS_DECODE_FAIL_MISSING_RR_LEN       },
        { L("resource record length field is zero"),            FR_DNS_DECODE_FAIL_ZERO_RR_LEN  },
        { L("resource record length overflows the packet"),     FR_DNS_DECODE_FAIL_RR_OVERFLOWS_PACKET  },
        { L("more resource records than indicated in header"),  FR_DNS_DECODE_FAIL_TOO_MANY_RRS },
        { L("fewer resource records than indicated in header"), FR_DNS_DECODE_FAIL_TOO_FEW_RRS          },
        { L("pointer overflows packet"),                        FR_DNS_DECODE_FAIL_POINTER_OVERFLOWS_PACKET     },
        { L("pointer points to packet header"),                 FR_DNS_DECODE_FAIL_POINTER_TO_HEADER            },
        { L("pointer does not point to a label"),               FR_DNS_DECODE_FAIL_POINTER_TO_NON_LABEL         },
        { L("pointer creates a loop"),                          FR_DNS_DECODE_FAIL_POINTER_LOOPS                },
        { L("invalid pointer"),                                 FR_DNS_DECODE_FAIL_INVALID_POINTER              },
        { L("label overflows the packet"),                      FR_DNS_DECODE_FAIL_LABEL_OVERFLOWS_PACKET       },
        { L("too many characters in label"),                    FR_DNS_DECODE_FAIL_LABEL_TOO_LONG               },
        { L("query record header is missing"),                  FR_DNS_DECODE_FAIL_MISSING_QD_HEADER            },
        { L("missing TLV header in OPT RR"),                    FR_DNS_DECODE_FAIL_MISSING_TLV_HEADER           },
        { L("TLV overflows enclosing RR"),                      FR_DNS_DECODE_FAIL_TLV_OVERFLOWS_RR             },
};
size_t fr_dns_reason_fail_table_len = NUM_ELEMENTS(fr_dns_reason_fail_table);
 
static ssize_t decode_proto(TALLOC_CTX *ctx, fr_pair_list_t *out, uint8_t const *data, size_t data_len, void *proto_ctx)
{
        fr_dns_ctx_t *packet_ctx = proto_ctx;
        fr_dns_decode_fail_t reason;
 
        if (data_len > 65535) return -1; /* packet is too big */
 
        /*
         *      Allow queries or answers
         */
        if (!fr_dns_packet_ok(data, data_len, true, &reason)) {
                if (reason != FR_DNS_DECODE_FAIL_UNEXPECTED) goto fail;
 
                if (!fr_dns_packet_ok(data, data_len, false, &reason)) {
                fail:
                        fr_strerror_printf("DNS packet malformed - %s",
                                           fr_table_str_by_value(fr_dns_reason_fail_table, reason, "<INVALID>"));
                        return -1;
                }
        }
 
        packet_ctx->packet = data;
        packet_ctx->packet_len = data_len;
        packet_ctx->lb = fr_dns_labels_get(data, data_len, true);
        fr_assert(packet_ctx->lb != NULL);
 
        return fr_dns_decode(ctx, out, data, data_len,  packet_ctx);
}
 
/*
 *      Test points
 */
extern fr_test_point_pair_decode_t dns_tp_decode_pair;
fr_test_point_pair_decode_t dns_tp_decode_pair = {
        .test_ctx       = decode_test_ctx,
        .func           = decode_rr
};
 
extern fr_test_point_proto_decode_t dns_tp_decode_proto;
fr_test_point_proto_decode_t dns_tp_decode_proto = {
        .test_ctx       = decode_test_ctx,
        .func           = decode_proto
};