check ensure seekback 4 bytes before read 4 bytes from pb,
and seek back 4 byte from current position after read 4 bytes.
fix segfaults:
READ of size 1 at 0x6100000003b7 thread T0
#0 0x7f928d in flv_same_video_codec ffmpeg/libavformat/flvdec.c:317:29
#1 0x7f928d in flv_read_packet ffmpeg/libavformat/flvdec.c:1177
#2 0x6ff32f in ff_read_packet ffmpeg/libavformat/demux.c:575:15
#3 0x70a2fd in read_frame_internal ffmpeg/libavformat/demux.c:1263:15
#4 0x71d158 in avformat_find_stream_info ffmpeg/libavformat/demux.c:2634:15
#5 0x4c821b in LLVMFuzzerTestOneInput
ffmpeg/tools/target_dem_fuzzer.c:206:11
Signed-off-by: Steven Liu <l...@chinaffmpeg.org>
---
libavformat/flvdec.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/libavformat/flvdec.c b/libavformat/flvdec.c
index 3fe21622f7..38f34567dd 100644
--- a/libavformat/flvdec.c
+++ b/libavformat/flvdec.c
@@ -35,6 +35,7 @@
#include "libavutil/intreadwrite.h"
#include "libavutil/mathematics.h"
#include "avformat.h"
+#include "avio_internal.h"
#include "demux.h"
#include "internal.h"
#include "flv.h"
@@ -313,8 +314,14 @@ static int flv_same_video_codec(AVFormatContext *s,
AVCodecParameters *vpar, int
return 1;
if (flv->exheader) {
- uint8_t *codec_id_str = (uint8_t *)s->pb->buf_ptr;
- uint32_t codec_id = codec_id_str[3] | codec_id_str[2] << 8 |
codec_id_str[1] << 16 | codec_id_str[0] << 24;
+ uint32_t codec_id = 0;
+ int ret = ffio_ensure_seekback(s->pb, 4);
+ if (ret < 0) {
+ av_log(s, AV_LOG_WARNING, "Could not ensure seekback, because %s",
av_err2str(ret));
+ return 0;
+ }
+ codec_id = avio_rb32(s->pb);
+ avio_seek(s->pb, -4, SEEK_CUR);
switch(codec_id) {
case MKBETAG('h', 'v', 'c', '1'):
return vpar->codec_id == AV_CODEC_ID_HEVC;
--
2.40.0
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