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avformat/dhav: Fix incorrect non-DHAV chunk skipping logic 

DAV files may contain a variable length padding in between chunks
filled with 0xff bytes. The current skipping logic is incorrect as it
may skip over DHAV chunks not appearing sequentially in the file.

We now look for the 'DHAV' tag using a byte-by-byte search in order
to handle such situations. Also the dhav->last_good_pos field will
not be updated while skipping unrecognized data.
This commit is contained in:
Idan Freiberg 2021-01-13 14:34:54 +02:00 committed by Paul B Mahol
parent f6477ac9f4
commit a6912e5b88
1 changed files with 3 additions and 12 deletions
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13
libavformat/dhav.c
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@ -173,18 +173,9 @@ static int read_chunk(AVFormatContext *s)
if (avio_feof(s->pb))
return AVERROR_EOF;
if (avio_rl32(s->pb) != MKTAG('D','H','A','V') && dhav->last_good_pos < INT64_MAX - 0x8000) {
dhav->last_good_pos += 0x8000;
avio_seek(s->pb, dhav->last_good_pos, SEEK_SET);
while (avio_rl32(s->pb) != MKTAG('D','H','A','V')) {
if (avio_feof(s->pb) || dhav->last_good_pos >= INT64_MAX - 0x8000)
while (avio_r8(s->pb) != 'D' || avio_r8(s->pb) != 'H' || avio_r8(s->pb) != 'A' || avio_r8(s->pb) != 'V') {
if (avio_feof(s->pb))
return AVERROR_EOF;
dhav->last_good_pos += 0x8000;
ret = avio_skip(s->pb, 0x8000 - 4);
if (ret < 0)
return ret;
}
}
start = avio_tell(s->pb) - 4;