/*      $OpenBSD: bs_cbs.c,v 1.3 2024/05/25 15:12:47 tb Exp $   */
/*
 * Copyright (c) 2014, Google Inc.
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <stdint.h>
#include <stdlib.h>
#include <string.h>

#include "bytestring.h"

void
CBS_init(CBS *cbs, const uint8_t *data, size_t len)
{
        cbs->data = data;
        cbs->initial_len = len;
        cbs->len = len;
}

void
CBS_dup(const CBS *cbs, CBS *out)
{
        CBS_init(out, CBS_data(cbs), CBS_len(cbs));
        out->initial_len = cbs->initial_len;
}

static int
cbs_get(CBS *cbs, const uint8_t **p, size_t n)
{
        if (cbs->len < n)
                return 0;

        *p = cbs->data;
        cbs->data += n;
        cbs->len -= n;
        return 1;
}

static int
cbs_peek(CBS *cbs, const uint8_t **p, size_t n)
{
        if (cbs->len < n)
                return 0;

        *p = cbs->data;
        return 1;
}

size_t
CBS_offset(const CBS *cbs)
{
        return cbs->initial_len - cbs->len;
}

int
CBS_skip(CBS *cbs, size_t len)
{
        const uint8_t *dummy;
        return cbs_get(cbs, &dummy, len);
}

const uint8_t *
CBS_data(const CBS *cbs)
{
        return cbs->data;
}

size_t
CBS_len(const CBS *cbs)
{
        return cbs->len;
}

int
CBS_stow(const CBS *cbs, uint8_t **out_ptr, size_t *out_len)
{
        free(*out_ptr);
        *out_ptr = NULL;
        *out_len = 0;

        if (cbs->len == 0)
                return 1;

        if ((*out_ptr = malloc(cbs->len)) == NULL)
                return 0;

        memcpy(*out_ptr, cbs->data, cbs->len);

        *out_len = cbs->len;
        return 1;
}

int
CBS_strdup(const CBS *cbs, char **out_ptr)
{
        free(*out_ptr);
        *out_ptr = NULL;

        if (CBS_contains_zero_byte(cbs))
                return 0;

        *out_ptr = strndup((const char *)cbs->data, cbs->len);
        return (*out_ptr != NULL);
}

int
CBS_write_bytes(const CBS *cbs, uint8_t *dst, size_t dst_len, size_t *copied)
{
        if (dst_len < cbs->len)
                return 0;

        memmove(dst, cbs->data, cbs->len);

        if (copied != NULL)
                *copied = cbs->len;

        return 1;
}

int
CBS_contains_zero_byte(const CBS *cbs)
{
        return memchr(cbs->data, 0, cbs->len) != NULL;
}

int
CBS_mem_equal(const CBS *cbs, const uint8_t *data, size_t len)
{
        if (len != cbs->len)
                return 0;

        return timingsafe_memcmp(cbs->data, data, len) == 0;
}

static int
cbs_get_u(CBS *cbs, uint32_t *out, size_t len)
{
        uint32_t result = 0;
        size_t i;
        const uint8_t *data;

        if (len < 1 || len > 4)
                return 0;

        if (!cbs_get(cbs, &data, len))
                return 0;

        for (i = 0; i < len; i++) {
                result <<= 8;
                result |= data[i];
        }
        *out = result;
        return 1;
}

int
CBS_get_u8(CBS *cbs, uint8_t *out)
{
        const uint8_t *v;

        if (!cbs_get(cbs, &v, 1))
                return 0;

        *out = *v;
        return 1;
}

int
CBS_get_u16(CBS *cbs, uint16_t *out)
{
        uint32_t v;

        if (!cbs_get_u(cbs, &v, 2))
                return 0;

        *out = v;
        return 1;
}

int
CBS_get_u24(CBS *cbs, uint32_t *out)
{
        return cbs_get_u(cbs, out, 3);
}

int
CBS_get_u32(CBS *cbs, uint32_t *out)
{
        return cbs_get_u(cbs, out, 4);
}

int
CBS_get_u64(CBS *cbs, uint64_t *out)
{
        uint32_t a, b;

        if (cbs->len < 8)
                return 0;

        if (!CBS_get_u32(cbs, &a))
                return 0;
        if (!CBS_get_u32(cbs, &b))
                return 0;

        *out = (uint64_t)a << 32 | b;
        return 1;
}

int
CBS_get_last_u8(CBS *cbs, uint8_t *out)
{
        if (cbs->len == 0)
                return 0;

        *out = cbs->data[cbs->len - 1];
        cbs->len--;
        return 1;
}

int
CBS_get_bytes(CBS *cbs, CBS *out, size_t len)
{
        const uint8_t *v;

        if (!cbs_get(cbs, &v, len))
                return 0;

        CBS_init(out, v, len);
        return 1;
}

static int
cbs_get_length_prefixed(CBS *cbs, CBS *out, size_t len_len)
{
        uint32_t len;

        if (!cbs_get_u(cbs, &len, len_len))
                return 0;

        return CBS_get_bytes(cbs, out, len);
}

int
CBS_get_u8_length_prefixed(CBS *cbs, CBS *out)
{
        return cbs_get_length_prefixed(cbs, out, 1);
}

int
CBS_get_u16_length_prefixed(CBS *cbs, CBS *out)
{
        return cbs_get_length_prefixed(cbs, out, 2);
}

int
CBS_get_u24_length_prefixed(CBS *cbs, CBS *out)
{
        return cbs_get_length_prefixed(cbs, out, 3);
}

static int
cbs_peek_u(CBS *cbs, uint32_t *out, size_t len)
{
        uint32_t result = 0;
        size_t i;
        const uint8_t *data;

        if (len < 1 || len > 4)
                return 0;

        if (!cbs_peek(cbs, &data, len))
                return 0;

        for (i = 0; i < len; i++) {
                result <<= 8;
                result |= data[i];
        }
        *out = result;
        return 1;
}

int
CBS_peek_u8(CBS *cbs, uint8_t *out)
{
        const uint8_t *v;

        if (!cbs_peek(cbs, &v, 1))
                return 0;

        *out = *v;
        return 1;
}

int
CBS_peek_u16(CBS *cbs, uint16_t *out)
{
        uint32_t v;

        if (!cbs_peek_u(cbs, &v, 2))
                return 0;

        *out = v;
        return 1;
}

int
CBS_peek_u24(CBS *cbs, uint32_t *out)
{
        return cbs_peek_u(cbs, out, 3);
}

int
CBS_peek_u32(CBS *cbs, uint32_t *out)
{
        return cbs_peek_u(cbs, out, 4);
}

int
CBS_peek_last_u8(CBS *cbs, uint8_t *out)
{
        if (cbs->len == 0)
                return 0;

        *out = cbs->data[cbs->len - 1];
        return 1;
}

int
CBS_get_any_asn1_element(CBS *cbs, CBS *out, unsigned int *out_tag,
    size_t *out_header_len)
{
        return cbs_get_any_asn1_element_internal(cbs, out, out_tag,
            out_header_len, 1);
}

/*
 * Review X.690 for details on ASN.1 DER encoding.
 *
 * If non-strict mode is enabled, then DER rules are relaxed
 * for indefinite constructs (violates DER but a little closer to BER).
 * Non-strict mode should only be used by bs_ber.c
 *
 * Sections 8, 10 and 11 for DER encoding
 */
int
cbs_get_any_asn1_element_internal(CBS *cbs, CBS *out, unsigned int *out_tag,
    size_t *out_header_len, int strict)
{
        uint8_t tag, length_byte;
        CBS header = *cbs;
        CBS throwaway;
        size_t len;

        if (out == NULL)
                out = &throwaway;

        /*
         * Get identifier octet and length octet.  Only 1 octet for each
         * is a CBS limitation.
         */
        if (!CBS_get_u8(&header, &tag) || !CBS_get_u8(&header, &length_byte))
                return 0;

        /* CBS limitation: long form tags are not supported. */
        if ((tag & 0x1f) == 0x1f)
                return 0;

        if (out_tag != NULL)
                *out_tag = tag;

        if ((length_byte & 0x80) == 0) {
                /* Short form length. */
                len = ((size_t) length_byte) + 2;
                if (out_header_len != NULL)
                        *out_header_len = 2;

        } else {
                /* Long form length. */
                const size_t num_bytes = length_byte & 0x7f;
                uint32_t len32;

                /* ASN.1 reserved value for future extensions */
                if (num_bytes == 0x7f)
                        return 0;

                /* Handle indefinite form length */
                if (num_bytes == 0) {
                        /* DER encoding doesn't allow for indefinite form. */
                        if (strict)
                                return 0;

                        /* Primitive cannot use indefinite in BER or DER. */
                        if ((tag & CBS_ASN1_CONSTRUCTED) == 0)
                                return 0;

                        /* Constructed, indefinite length allowed in BER. */
                        if (out_header_len != NULL)
                                *out_header_len = 2;
                        return CBS_get_bytes(cbs, out, 2);
                }

                /* CBS limitation. */
                if (num_bytes > 4)
                        return 0;

                if (!cbs_get_u(&header, &len32, num_bytes))
                        return 0;

                /* DER has a minimum length octet requirement. */
                if (len32 < 128)
                        /* Should have used short form instead */
                        return 0;

                if ((len32 >> ((num_bytes - 1) * 8)) == 0)
                        /* Length should have been at least one byte shorter. */
                        return 0;

                len = len32;
                if (len + 2 + num_bytes < len)
                        /* Overflow. */
                        return 0;

                len += 2 + num_bytes;
                if (out_header_len != NULL)
                        *out_header_len = 2 + num_bytes;
        }

        return CBS_get_bytes(cbs, out, len);
}

static int
cbs_get_asn1(CBS *cbs, CBS *out, unsigned int tag_value, int skip_header)
{
        size_t header_len;
        unsigned int tag;
        CBS throwaway;

        if (out == NULL)
                out = &throwaway;

        if (!CBS_get_any_asn1_element(cbs, out, &tag, &header_len) ||
            tag != tag_value)
                return 0;

        if (skip_header && !CBS_skip(out, header_len))
                return 0;

        return 1;
}

int
CBS_get_asn1(CBS *cbs, CBS *out, unsigned int tag_value)
{
        return cbs_get_asn1(cbs, out, tag_value, 1 /* skip header */);
}

int
CBS_get_asn1_element(CBS *cbs, CBS *out, unsigned int tag_value)
{
        return cbs_get_asn1(cbs, out, tag_value, 0 /* include header */);
}

int
CBS_peek_asn1_tag(const CBS *cbs, unsigned int tag_value)
{
        if (CBS_len(cbs) < 1)
                return 0;

        /*
         * Tag number 31 indicates the start of a long form number.
         * This is valid in ASN.1, but CBS only supports short form.
         */
        if ((tag_value & 0x1f) == 0x1f)
                return 0;

        return CBS_data(cbs)[0] == tag_value;
}

/* Encoding details are in ASN.1: X.690 section 8.3 */
int
CBS_get_asn1_uint64(CBS *cbs, uint64_t *out)
{
        CBS bytes;
        const uint8_t *data;
        size_t i, len;

        if (!CBS_get_asn1(cbs, &bytes, CBS_ASN1_INTEGER))
                return 0;

        *out = 0;
        data = CBS_data(&bytes);
        len = CBS_len(&bytes);

        if (len == 0)
                /* An INTEGER is encoded with at least one content octet. */
                return 0;

        if ((data[0] & 0x80) != 0)
                /* Negative number. */
                return 0;

        if (data[0] == 0 && len > 1 && (data[1] & 0x80) == 0)
                /* Violates smallest encoding rule: excessive leading zeros. */
                return 0;

        for (i = 0; i < len; i++) {
                if ((*out >> 56) != 0)
                        /* Too large to represent as a uint64_t. */
                        return 0;

                *out <<= 8;
                *out |= data[i];
        }

        return 1;
}

int
CBS_get_optional_asn1(CBS *cbs, CBS *out, int *out_present, unsigned int tag)
{
        if (CBS_peek_asn1_tag(cbs, tag)) {
                if (!CBS_get_asn1(cbs, out, tag))
                        return 0;

                *out_present = 1;
        } else {
                *out_present = 0;
        }
        return 1;
}

int
CBS_get_optional_asn1_octet_string(CBS *cbs, CBS *out, int *out_present,
    unsigned int tag)
{
        CBS child;
        int present;

        if (!CBS_get_optional_asn1(cbs, &child, &present, tag))
                return 0;

        if (present) {
                if (!CBS_get_asn1(&child, out, CBS_ASN1_OCTETSTRING) ||
                    CBS_len(&child) != 0)
                        return 0;
        } else {
                CBS_init(out, NULL, 0);
        }
        if (out_present)
                *out_present = present;

        return 1;
}

int
CBS_get_optional_asn1_uint64(CBS *cbs, uint64_t *out, unsigned int tag,
    uint64_t default_value)
{
        CBS child;
        int present;

        if (!CBS_get_optional_asn1(cbs, &child, &present, tag))
                return 0;

        if (present) {
                if (!CBS_get_asn1_uint64(&child, out) ||
                    CBS_len(&child) != 0)
                        return 0;
        } else {
                *out = default_value;
        }
        return 1;
}

int
CBS_get_optional_asn1_bool(CBS *cbs, int *out, unsigned int tag,
    int default_value)
{
        CBS child, child2;
        int present;

        if (!CBS_get_optional_asn1(cbs, &child, &present, tag))
                return 0;

        if (present) {
                uint8_t boolean;

                if (!CBS_get_asn1(&child, &child2, CBS_ASN1_BOOLEAN) ||
                    CBS_len(&child2) != 1 || CBS_len(&child) != 0)
                        return 0;

                boolean = CBS_data(&child2)[0];
                if (boolean == 0)
                        *out = 0;
                else if (boolean == 0xff)
                        *out = 1;
                else
                        return 0;

        } else {
                *out = default_value;
        }
        return 1;
}