drivers/firmware/google/vpd_decode.c

/*
 * vpd_decode.c
 *
 * Google VPD decoding routines.
 *
 * Copyright 2017 Google Inc.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License v2.0 as published by
 * the Free Software Foundation.
 *
 * This program 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 General Public License for more details.
 */

#include <linux/export.h>

#include "vpd_decode.h"

static int vpd_decode_len(const u32 max_len, const u8 *in,
			  u32 *length, u32 *decoded_len)
{
	u8 more;
	int i = 0;

	if (!length || !decoded_len)
		return VPD_FAIL;

	*length = 0;
	do {
		if (i >= max_len)
			return VPD_FAIL;

		more = in[i] & 0x80;
		*length <<= 7;
		*length |= in[i] & 0x7f;
		++i;
	} while (more);

	*decoded_len = i;
	return VPD_OK;
}

static int vpd_decode_entry(const u32 max_len, const u8 *input_buf,
			    u32 *_consumed, const u8 **entry, u32 *entry_len)
{
	u32 decoded_len;
	u32 consumed = *_consumed;

	if (vpd_decode_len(max_len - consumed, &input_buf[consumed],
			   entry_len, &decoded_len) != VPD_OK)
		return VPD_FAIL;
	if (max_len - consumed < decoded_len)
		return VPD_FAIL;

	consumed += decoded_len;
	*entry = input_buf + consumed;

	/* entry_len is untrusted data and must be checked again. */
	if (max_len - consumed < *entry_len)
		return VPD_FAIL;

	consumed += *entry_len;
	*_consumed = consumed;
	return VPD_OK;
}

int vpd_decode_string(const u32 max_len, const u8 *input_buf, u32 *consumed,
		      vpd_decode_callback callback, void *callback_arg)
{
	int type;
	u32 key_len;
	u32 value_len;
	const u8 *key;
	const u8 *value;

	/* type */
	if (*consumed >= max_len)
		return VPD_FAIL;

	type = input_buf[*consumed];

	switch (type) {
	case VPD_TYPE_INFO:
	case VPD_TYPE_STRING:
		(*consumed)++;

		if (vpd_decode_entry(max_len, input_buf, consumed, &key,
				     &key_len) != VPD_OK)
			return VPD_FAIL;

		if (vpd_decode_entry(max_len, input_buf, consumed, &value,
				     &value_len) != VPD_OK)
			return VPD_FAIL;

		if (type == VPD_TYPE_STRING)
			return callback(key, key_len, value, value_len,
					callback_arg);
		break;

	default:
		return VPD_FAIL;
	}

	return VPD_OK;
}