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oggdec: verify page checksum

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This makes decoding far more robust, since OggS, the ogg magic,
can be commonly found randomly in streams, which previously made
the demuxer think there's a new stream or a change in such.
This commit is contained in:
Lynne 2020-04-28 12:52:11 +01:00
parent f619e1ec66
commit 9ad47762c1
No known key found for this signature in database
GPG Key ID: A2FEA5F03F034464
1 changed files with 34 additions and 12 deletions
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40
libavformat/oggdec.c
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@ -31,6 +31,7 @@
#include <stdio.h>
#include "libavutil/avassert.h"
#include "libavutil/intreadwrite.h"
#include "avio_internal.h"
#include "oggdec.h"
#include "avformat.h"
#include "internal.h"
@ -321,8 +322,9 @@ static int ogg_read_page(AVFormatContext *s, int *sid)
int flags, nsegs;
uint64_t gp;
uint32_t serial;
uint32_t crc, crc_tmp;
int size = 0, idx;
int64_t page_pos;
int64_t version, page_pos;
uint8_t sync[4];
uint8_t segments[255];
uint8_t *readout_buf;
@ -359,15 +361,19 @@ static int ogg_read_page(AVFormatContext *s, int *sid)
return AVERROR_INVALIDDATA;
}
if (avio_r8(bc) != 0) { /* version */
av_log (s, AV_LOG_ERROR, "ogg page, unsupported version\n");
return AVERROR_INVALIDDATA;
}
/* 0x4fa9b05f = av_crc(AV_CRC_32_IEEE, 0x0, "OggS", 4) */
ffio_init_checksum(bc, ff_crc04C11DB7_update, 0x4fa9b05f);
version = avio_r8(bc);
flags = avio_r8(bc);
gp = avio_rl64(bc);
serial = avio_rl32(bc);
avio_skip(bc, 8); /* seq, crc */
avio_skip(bc, 4); /* seq */
crc_tmp = ffio_get_checksum(bc);
crc = avio_rb32(bc);
crc_tmp = ff_crc04C11DB7_update(crc_tmp, (uint8_t[4]){0}, 4);
ffio_init_checksum(bc, ff_crc04C11DB7_update, crc_tmp);
nsegs = avio_r8(bc);
page_pos = avio_tell(bc) - 27;
@ -376,9 +382,6 @@ static int ogg_read_page(AVFormatContext *s, int *sid)
if (ret < nsegs)
return ret < 0 ? ret : AVERROR_EOF;
if (avio_feof(bc))
return AVERROR_EOF;
for (i = 0; i < nsegs; i++)
size += segments[i];
@ -407,6 +410,25 @@ static int ogg_read_page(AVFormatContext *s, int *sid)
return ret < 0 ? ret : AVERROR_EOF;
}
if (crc ^ ffio_get_checksum(bc)) {
av_log(s, AV_LOG_ERROR, "CRC mismatch!\n");
if (idx < 0)
av_free(readout_buf);
avio_seek(bc, -size, SEEK_CUR);
return 0;
}
/* Since we're almost sure its a valid packet, checking the version after
* the checksum lets the demuxer be more tolerant */
if (version) {
av_log(s, AV_LOG_ERROR, "Invalid Ogg vers!\n");
if (idx < 0)
av_free(readout_buf);
avio_seek(bc, -size, SEEK_CUR);
return 0;
}
/* CRC is correct so we can be 99% sure there's an actual change here */
if (idx < 0) {
if (data_packets_seen(ogg))
idx = ogg_replace_stream(s, serial, size);