bs_cbb.c

/*	$OpenBSD: bs_cbb.c,v 1.30 2024/06/22 15:25:06 jsing 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"

#define CBB_INITIAL_SIZE 64

static int
cbb_init(CBB *cbb, uint8_t *buf, size_t cap)
{
	struct cbb_buffer_st *base;

	if ((base = calloc(1, sizeof(struct cbb_buffer_st))) == NULL)
		return 0;

	base->buf = buf;
	base->len = 0;
	base->cap = cap;
	base->can_resize = 1;

	cbb->base = base;
	cbb->is_top_level = 1;

	return 1;
}

int
CBB_init(CBB *cbb, size_t initial_capacity)
{
	uint8_t *buf = NULL;

	memset(cbb, 0, sizeof(*cbb));

	if (initial_capacity == 0)
		initial_capacity = CBB_INITIAL_SIZE;

	if ((buf = calloc(1, initial_capacity)) == NULL)
		return 0;

	if (!cbb_init(cbb, buf, initial_capacity)) {
		free(buf);
		return 0;
	}

	return 1;
}

int
CBB_init_fixed(CBB *cbb, uint8_t *buf, size_t len)
{
	memset(cbb, 0, sizeof(*cbb));

	if (!cbb_init(cbb, buf, len))
		return 0;

	cbb->base->can_resize = 0;

	return 1;
}

void
CBB_cleanup(CBB *cbb)
{
	if (cbb->base) {
		if (cbb->base->can_resize)
			freezero(cbb->base->buf, cbb->base->cap);
		free(cbb->base);
	}
	cbb->base = NULL;
	cbb->child = NULL;
}

static int
cbb_buffer_add(struct cbb_buffer_st *base, uint8_t **out, size_t len)
{
	size_t newlen;

	if (base == NULL)
		return 0;

	newlen = base->len + len;
	if (newlen < base->len)
		/* Overflow */
		return 0;

	if (newlen > base->cap) {
		size_t newcap = base->cap * 2;
		uint8_t *newbuf;

		if (!base->can_resize)
			return 0;

		if (newcap < base->cap || newcap < newlen)
			newcap = newlen;

		newbuf = recallocarray(base->buf, base->cap, newcap, 1);
		if (newbuf == NULL)
			return 0;

		base->buf = newbuf;
		base->cap = newcap;
	}

	if (out)
		*out = base->buf + base->len;

	base->len = newlen;
	return 1;
}

static int
cbb_add_u(CBB *cbb, uint32_t v, size_t len_len)
{
	uint8_t *buf;
	size_t i;

	if (len_len == 0)
		return 1;

	if (len_len > 4)
		return 0;

	if (!CBB_flush(cbb) || !cbb_buffer_add(cbb->base, &buf, len_len))
		return 0;

	for (i = len_len - 1; i < len_len; i--) {
		buf[i] = v;
		v >>= 8;
	}
	return 1;
}

int
CBB_finish(CBB *cbb, uint8_t **out_data, size_t *out_len)
{
	if (!cbb->is_top_level)
		return 0;

	if (!CBB_flush(cbb))
		return 0;

	if (cbb->base->can_resize && (out_data == NULL || out_len == NULL))
		/*
		 * |out_data| and |out_len| can only be NULL if the CBB is
		 * fixed.
		 */
		return 0;

	if (out_data != NULL && *out_data != NULL)
		return 0;

	if (out_data != NULL)
		*out_data = cbb->base->buf;

	if (out_len != NULL)
		*out_len = cbb->base->len;

	cbb->base->buf = NULL;
	CBB_cleanup(cbb);
	return 1;
}

/*
 * CBB_flush recurses and then writes out any pending length prefix. The current
 * length of the underlying base is taken to be the length of the
 * length-prefixed data.
 */
int
CBB_flush(CBB *cbb)
{
	size_t child_start, i, len;

	if (cbb->base == NULL)
		return 0;

	if (cbb->child == NULL || cbb->pending_len_len == 0)
		return 1;

	child_start = cbb->offset + cbb->pending_len_len;

	if (!CBB_flush(cbb->child) || child_start < cbb->offset ||
	    cbb->base->len < child_start)
		return 0;

	len = cbb->base->len - child_start;

	if (cbb->pending_is_asn1) {
		/*
		 * For ASN.1, we assumed that we were using short form which
		 * only requires a single byte for the length octet.
		 *
		 * If it turns out that we need long form, we have to move
		 * the contents along in order to make space for more length
		 * octets.
		 */
		size_t len_len = 1;  /* total number of length octets */
		uint8_t initial_length_byte;

		/* We already wrote 1 byte for the length. */
		if (cbb->pending_len_len != 1)
			return 0;

		/* Check for long form */
		if (len > 0xfffffffe)
			return 0;	/* 0xffffffff is reserved */
		else if (len > 0xffffff)
			len_len = 5;
		else if (len > 0xffff)
			len_len = 4;
		else if (len > 0xff)
			len_len = 3;
		else if (len > 0x7f)
			len_len = 2;

		if (len_len == 1) {
			/* For short form, the initial byte is the length. */
			initial_length_byte = len;
			len = 0;

		} else {
			/*
			 * For long form, the initial byte is the number of
			 * subsequent length octets (plus bit 8 set).
			 */
			initial_length_byte = 0x80 | (len_len - 1);

			/*
			 * We need to move the contents along in order to make
			 * space for the long form length octets.
			 */
			size_t extra_bytes = len_len - 1;
			if (!cbb_buffer_add(cbb->base, NULL, extra_bytes))
				return 0;

			memmove(cbb->base->buf + child_start + extra_bytes,
			    cbb->base->buf + child_start, len);
		}
		cbb->base->buf[cbb->offset++] = initial_length_byte;
		cbb->pending_len_len = len_len - 1;
	}

	for (i = cbb->pending_len_len - 1; i < cbb->pending_len_len; i--) {
		cbb->base->buf[cbb->offset + i] = len;
		len >>= 8;
	}
	if (len != 0)
		return 0;

	cbb->child->base = NULL;
	cbb->child = NULL;
	cbb->pending_len_len = 0;
	cbb->pending_is_asn1 = 0;
	cbb->offset = 0;

	return 1;
}

void
CBB_discard_child(CBB *cbb)
{
	if (cbb->child == NULL)
		return;

	cbb->base->len = cbb->offset;

	cbb->child->base = NULL;
	cbb->child = NULL;
	cbb->pending_len_len = 0;
	cbb->pending_is_asn1 = 0;
	cbb->offset = 0;
}

static int
cbb_add_length_prefixed(CBB *cbb, CBB *out_contents, size_t len_len)
{
	uint8_t *prefix_bytes;

	if (!CBB_flush(cbb))
		return 0;

	cbb->offset = cbb->base->len;
	if (!cbb_buffer_add(cbb->base, &prefix_bytes, len_len))
		return 0;

	memset(prefix_bytes, 0, len_len);
	memset(out_contents, 0, sizeof(CBB));
	out_contents->base = cbb->base;
	cbb->child = out_contents;
	cbb->pending_len_len = len_len;
	cbb->pending_is_asn1 = 0;

	return 1;
}

int
CBB_add_u8_length_prefixed(CBB *cbb, CBB *out_contents)
{
	return cbb_add_length_prefixed(cbb, out_contents, 1);
}

int
CBB_add_u16_length_prefixed(CBB *cbb, CBB *out_contents)
{
	return cbb_add_length_prefixed(cbb, out_contents, 2);
}

int
CBB_add_u24_length_prefixed(CBB *cbb, CBB *out_contents)
{
	return cbb_add_length_prefixed(cbb, out_contents, 3);
}

int
CBB_add_u32_length_prefixed(CBB *cbb, CBB *out_contents)
{
	return cbb_add_length_prefixed(cbb, out_contents, 4);
}

int
CBB_add_asn1(CBB *cbb, CBB *out_contents, unsigned int tag)
{
	if (tag > UINT8_MAX)
		return 0;

	/* Long form identifier octets are not supported. */
	if ((tag & 0x1f) == 0x1f)
		return 0;

	/* Short-form identifier octet only needs a single byte */
	if (!CBB_flush(cbb) || !CBB_add_u8(cbb, tag))
		return 0;

	/*
	 * Add 1 byte to cover the short-form length octet case.  If it turns
	 * out we need long-form, it will be extended later.
	 */
	cbb->offset = cbb->base->len;
	if (!CBB_add_u8(cbb, 0))
		return 0;

	memset(out_contents, 0, sizeof(CBB));
	out_contents->base = cbb->base;
	cbb->child = out_contents;
	cbb->pending_len_len = 1;
	cbb->pending_is_asn1 = 1;

	return 1;
}

int
CBB_add_bytes(CBB *cbb, const uint8_t *data, size_t len)
{
	uint8_t *dest;

	if (!CBB_flush(cbb) || !cbb_buffer_add(cbb->base, &dest, len))
		return 0;

	memcpy(dest, data, len);
	return 1;
}

int
CBB_add_space(CBB *cbb, uint8_t **out_data, size_t len)
{
	if (!CBB_flush(cbb) || !cbb_buffer_add(cbb->base, out_data, len))
		return 0;

	memset(*out_data, 0, len);
	return 1;
}

int
CBB_add_u8(CBB *cbb, size_t value)
{
	if (value > UINT8_MAX)
		return 0;

	return cbb_add_u(cbb, (uint32_t)value, 1);
}

int
CBB_add_u16(CBB *cbb, size_t value)
{
	if (value > UINT16_MAX)
		return 0;

	return cbb_add_u(cbb, (uint32_t)value, 2);
}

int
CBB_add_u24(CBB *cbb, size_t value)
{
	if (value > 0xffffffUL)
		return 0;

	return cbb_add_u(cbb, (uint32_t)value, 3);
}

int
CBB_add_u32(CBB *cbb, size_t value)
{
	if (value > 0xffffffffUL)
		return 0;

	return cbb_add_u(cbb, (uint32_t)value, 4);
}

int
CBB_add_u64(CBB *cbb, uint64_t value)
{
	uint32_t a, b;

	a = value >> 32;
	b = value & 0xffffffff;

	if (!CBB_add_u32(cbb, a))
		return 0;
	return CBB_add_u32(cbb, b);
}

int
CBB_add_asn1_uint64(CBB *cbb, uint64_t value)
{
	CBB child;
	size_t i;
	int started = 0;

	if (!CBB_add_asn1(cbb, &child, CBS_ASN1_INTEGER))
		return 0;

	for (i = 0; i < 8; i++) {
		uint8_t byte = (value >> 8 * (7 - i)) & 0xff;

		/*
		 * ASN.1 restriction: first 9 bits cannot be all zeroes or
		 * all ones.  Since this function only encodes unsigned
		 * integers, the only concerns are not encoding leading
		 * zeros and adding a padding byte if necessary.
		 *
		 * In practice, this means:
		 * 1) Skip leading octets of all zero bits in the value
		 * 2) After skipping the leading zero octets, if the next 9
		 *    bits are all ones, add an all zero prefix octet (and
		 *    set the high bit of the prefix octet if negative).
		 *
		 * Additionally, for an unsigned value, add an all zero
		 * prefix if the high bit of the first octet would be one.
		 */
		if (!started) {
			if (byte == 0)
				/* Don't encode leading zeros. */
				continue;

			/*
			 * If the high bit is set, add a padding byte to make it
			 * unsigned.
			 */
			if ((byte & 0x80) && !CBB_add_u8(&child, 0))
				return 0;

			started = 1;
		}
		if (!CBB_add_u8(&child, byte))
			return 0;
	}

	/* 0 is encoded as a single 0, not the empty string. */
	if (!started && !CBB_add_u8(&child, 0))
		return 0;

	return CBB_flush(cbb);
}