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.
Patch attached.
>From 61759b6b1ef3ca813eb39ee9ace2342eb121b3b0 Mon Sep 17 00:00:00 2001
From: Lynne <d...@lynne.ee>
Date: Tue, 28 Apr 2020 12:52:11 +0100
Subject: [PATCH 2/3] oggdec: verify page checksum
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.
---
libavformat/oggdec.c | 21 ++++++++++++++++++++-
1 file changed, 20 insertions(+), 1 deletion(-)
diff --git a/libavformat/oggdec.c b/libavformat/oggdec.c
index f67cf42e82..05cea2528b 100644
--- a/libavformat/oggdec.c
+++ b/libavformat/oggdec.c
@@ -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"
@@ -321,6 +322,7 @@ 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;
uint8_t sync[4];
@@ -359,6 +361,9 @@ static int ogg_read_page(AVFormatContext *s, int *sid)
return AVERROR_INVALIDDATA;
}
+ /* 0x4fa9b05f = av_crc(AV_CRC_32_IEEE, 0x0, "OggS", 4) */
+ ffio_init_checksum(bc, ff_crc04C11DB7_update, 0x4fa9b05f);
+
if (avio_r8(bc) != 0) { /* version */
av_log (s, AV_LOG_ERROR, "ogg page, unsupported version\n");
return AVERROR_INVALIDDATA;
@@ -367,7 +372,12 @@ static int ogg_read_page(AVFormatContext *s, int *sid)
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;
@@ -407,6 +417,15 @@ 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;
+ }
+
+ /* 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);
--
2.26.2
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