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FFmpeg/libavcodec/ac3_parser.c
James Almer 4c35bb53f9 avcodec/ac3_parser: improve false positive detection when parsing sync frames 
A two byte sync word is not enough to ensure we got a real syncframe, nor are
all the range checks we do in the first seven bytes. Do therefore an integrity
check for the sync frame in order to prevent the parser from filling avctx with
bogus information.

Signed-off-by: James Almer <jamrial@gmail.com>
2022-10-26 10:18:33 -03:00

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/*
* AC-3 parser
* Copyright (c) 2003 Fabrice Bellard
* Copyright (c) 2003 Michael Niedermayer
*
* This file is part of FFmpeg.
*
* FFmpeg 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.
*
* FFmpeg 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 FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "config.h"
#include "config_components.h"
#include "libavutil/channel_layout.h"
#include "parser.h"
#include "ac3defs.h"
#include "ac3tab.h"
#include "ac3_parser.h"
#include "ac3_parser_internal.h"
#include "aac_ac3_parser.h"
#include "get_bits.h"
#define AC3_HEADER_SIZE 7
#if CONFIG_AC3_PARSER
static const uint8_t eac3_blocks[4] = {
1, 2, 3, 6
};
/**
* Table for center mix levels
* reference: Section 5.4.2.4 cmixlev
*/
static const uint8_t center_levels[4] = { 4, 5, 6, 5 };
/**
* Table for surround mix levels
* reference: Section 5.4.2.5 surmixlev
*/
static const uint8_t surround_levels[4] = { 4, 6, 7, 6 };
int ff_ac3_find_syncword(const uint8_t *buf, int buf_size)
{
int i;
for (i = 1; i < buf_size; i += 2) {
if (buf[i] == 0x77 || buf[i] == 0x0B) {
if ((buf[i] ^ buf[i-1]) == (0x77 ^ 0x0B)) {
i--;
break;
} else if ((buf[i] ^ buf[i+1]) == (0x77 ^ 0x0B)) {
break;
}
}
}
if (i >= buf_size)
return AVERROR_INVALIDDATA;
return i;
}
int ff_ac3_parse_header(GetBitContext *gbc, AC3HeaderInfo *hdr)
{
int frame_size_code;
memset(hdr, 0, sizeof(*hdr));
hdr->sync_word = get_bits(gbc, 16);
if(hdr->sync_word != 0x0B77)
return AAC_AC3_PARSE_ERROR_SYNC;
/* read ahead to bsid to distinguish between AC-3 and E-AC-3 */
hdr->bitstream_id = show_bits_long(gbc, 29) & 0x1F;
if(hdr->bitstream_id > 16)
return AAC_AC3_PARSE_ERROR_BSID;
hdr->num_blocks = 6;
hdr->ac3_bit_rate_code = -1;
/* set default mix levels */
hdr->center_mix_level = 5; // -4.5dB
hdr->surround_mix_level = 6; // -6.0dB
/* set default dolby surround mode */
hdr->dolby_surround_mode = AC3_DSURMOD_NOTINDICATED;
if(hdr->bitstream_id <= 10) {
/* Normal AC-3 */
hdr->crc1 = get_bits(gbc, 16);
hdr->sr_code = get_bits(gbc, 2);
if(hdr->sr_code == 3)
return AAC_AC3_PARSE_ERROR_SAMPLE_RATE;
frame_size_code = get_bits(gbc, 6);
if(frame_size_code > 37)
return AAC_AC3_PARSE_ERROR_FRAME_SIZE;
hdr->ac3_bit_rate_code = (frame_size_code >> 1);
skip_bits(gbc, 5); // skip bsid, already got it
hdr->bitstream_mode = get_bits(gbc, 3);
hdr->channel_mode = get_bits(gbc, 3);
if(hdr->channel_mode == AC3_CHMODE_STEREO) {
hdr->dolby_surround_mode = get_bits(gbc, 2);
} else {
if((hdr->channel_mode & 1) && hdr->channel_mode != AC3_CHMODE_MONO)
hdr-> center_mix_level = center_levels[get_bits(gbc, 2)];
if(hdr->channel_mode & 4)
hdr->surround_mix_level = surround_levels[get_bits(gbc, 2)];
}
hdr->lfe_on = get_bits1(gbc);
hdr->sr_shift = FFMAX(hdr->bitstream_id, 8) - 8;
hdr->sample_rate = ff_ac3_sample_rate_tab[hdr->sr_code] >> hdr->sr_shift;
hdr->bit_rate = (ff_ac3_bitrate_tab[hdr->ac3_bit_rate_code] * 1000) >> hdr->sr_shift;
hdr->channels = ff_ac3_channels_tab[hdr->channel_mode] + hdr->lfe_on;
hdr->frame_size = ff_ac3_frame_size_tab[frame_size_code][hdr->sr_code] * 2;
hdr->frame_type = EAC3_FRAME_TYPE_AC3_CONVERT; //EAC3_FRAME_TYPE_INDEPENDENT;
hdr->substreamid = 0;
} else {
/* Enhanced AC-3 */
hdr->crc1 = 0;
hdr->frame_type = get_bits(gbc, 2);
if(hdr->frame_type == EAC3_FRAME_TYPE_RESERVED)
return AAC_AC3_PARSE_ERROR_FRAME_TYPE;
hdr->substreamid = get_bits(gbc, 3);
hdr->frame_size = (get_bits(gbc, 11) + 1) << 1;
if(hdr->frame_size < AC3_HEADER_SIZE)
return AAC_AC3_PARSE_ERROR_FRAME_SIZE;
hdr->sr_code = get_bits(gbc, 2);
if (hdr->sr_code == 3) {
int sr_code2 = get_bits(gbc, 2);
if(sr_code2 == 3)
return AAC_AC3_PARSE_ERROR_SAMPLE_RATE;
hdr->sample_rate = ff_ac3_sample_rate_tab[sr_code2] / 2;
hdr->sr_shift = 1;
} else {
hdr->num_blocks = eac3_blocks[get_bits(gbc, 2)];
hdr->sample_rate = ff_ac3_sample_rate_tab[hdr->sr_code];
hdr->sr_shift = 0;
}
hdr->channel_mode = get_bits(gbc, 3);
hdr->lfe_on = get_bits1(gbc);
hdr->bit_rate = 8LL * hdr->frame_size * hdr->sample_rate /
(hdr->num_blocks * 256);
hdr->channels = ff_ac3_channels_tab[hdr->channel_mode] + hdr->lfe_on;
}
hdr->channel_layout = ff_ac3_channel_layout_tab[hdr->channel_mode];
if (hdr->lfe_on)
hdr->channel_layout |= AV_CH_LOW_FREQUENCY;
return 0;
}
// TODO: Better way to pass AC3HeaderInfo fields to mov muxer.
int avpriv_ac3_parse_header(AC3HeaderInfo **phdr, const uint8_t *buf,
size_t size)
{
GetBitContext gb;
AC3HeaderInfo *hdr;
int err;
if (!*phdr)
*phdr = av_mallocz(sizeof(AC3HeaderInfo));
if (!*phdr)
return AVERROR(ENOMEM);
hdr = *phdr;
err = init_get_bits8(&gb, buf, size);
if (err < 0)
return AVERROR_INVALIDDATA;
err = ff_ac3_parse_header(&gb, hdr);
if (err < 0)
return AVERROR_INVALIDDATA;
return get_bits_count(&gb);
}
int av_ac3_parse_header(const uint8_t *buf, size_t size,
uint8_t *bitstream_id, uint16_t *frame_size)
{
GetBitContext gb;
AC3HeaderInfo hdr;
int err;
init_get_bits8(&gb, buf, size);
err = ff_ac3_parse_header(&gb, &hdr);
if (err < 0)
return AVERROR_INVALIDDATA;
*bitstream_id = hdr.bitstream_id;
*frame_size = hdr.frame_size;
return 0;
}
static int ac3_sync(uint64_t state, int *need_next_header, int *new_frame_start)
{
int err;
union {
uint64_t u64;
uint8_t u8[8 + AV_INPUT_BUFFER_PADDING_SIZE];
} tmp = { av_be2ne64(state) };
AC3HeaderInfo hdr;
GetBitContext gbc;
if (tmp.u8[1] == 0x77 && tmp.u8[2] == 0x0b) {
FFSWAP(uint8_t, tmp.u8[1], tmp.u8[2]);
FFSWAP(uint8_t, tmp.u8[3], tmp.u8[4]);
FFSWAP(uint8_t, tmp.u8[5], tmp.u8[6]);
}
init_get_bits(&gbc, tmp.u8+8-AC3_HEADER_SIZE, 54);
err = ff_ac3_parse_header(&gbc, &hdr);
if(err < 0)
return 0;
*new_frame_start = (hdr.frame_type != EAC3_FRAME_TYPE_DEPENDENT);
*need_next_header = *new_frame_start || (hdr.frame_type != EAC3_FRAME_TYPE_AC3_CONVERT);
return hdr.frame_size;
}
static av_cold int ac3_parse_init(AVCodecParserContext *s1)
{
AACAC3ParseContext *s = s1->priv_data;
s->header_size = AC3_HEADER_SIZE;
s->crc_ctx = av_crc_get_table(AV_CRC_16_ANSI);
s->sync = ac3_sync;
return 0;
}
const AVCodecParser ff_ac3_parser = {
.codec_ids = { AV_CODEC_ID_AC3, AV_CODEC_ID_EAC3 },
.priv_data_size = sizeof(AACAC3ParseContext),
.parser_init = ac3_parse_init,
.parser_parse = ff_aac_ac3_parse,
.parser_close = ff_parse_close,
};
#else
int avpriv_ac3_parse_header(AC3HeaderInfo **phdr, const uint8_t *buf,
size_t size)
{
return AVERROR(ENOSYS);
}
int av_ac3_parse_header(const uint8_t *buf, size_t size,
uint8_t *bitstream_id, uint16_t *frame_size)
{
return AVERROR(ENOSYS);
}
#endif
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