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avformat/matroskadec: Improve error/EOF checks III 

Up until now, when an element was skipped, it was relied upon
ffio_limit to make sure that there is enough data available to skip.
ffio_limit itself relies upon the availability of the file's size. As
this needn't be available, the check has been refined: First one byte
less than intended is skipped, then another byte is read, followed by a
check of the error flags.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
This commit is contained in:
Andreas Rheinhardt 2019-06-24 01:42:31 +02:00 committed by James Almer
parent a569a7b3bb
commit ff5ea59f7b
1 changed files with 17 additions and 7 deletions
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24
libavformat/matroskadec.c
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@ -1258,13 +1258,23 @@ static int ebml_parse_elem(MatroskaDemuxContext *matroska,
case EBML_STOP:
return 1;
default:
if (ffio_limit(pb, length) != length) {
// ffio_limit emits its own error message,
// so we don't have to.
return AVERROR(EIO);
}
res = avio_skip(pb, length);
res = res < 0 ? res : 0;
if (length) {
if (ffio_limit(pb, length) != length) {
// ffio_limit emits its own error message,
// so we don't have to.
return AVERROR(EIO);
}
if ((res = avio_skip(pb, length - 1)) >= 0) {
// avio_skip might take us past EOF. We check for this
// by skipping only length - 1 bytes, reading a byte and
// checking the error flags. This is done in order to check
// that the element has been properly skipped even when
// no filesize (that ffio_limit relies on) is available.
avio_r8(pb);
res = NEEDS_CHECKING;
}
} else
res = 0;
}
if (res) {
if (res == NEEDS_CHECKING) {