On 6/23/2019 8:42 PM, Andreas Rheinhardt wrote:
> 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.rheinha...@gmail.com>
> ---
> libavformat/matroskadec.c | 24 +++++++++++++++++-------
> 1 file changed, 17 insertions(+), 7 deletions(-)
>
> diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
> index 1db7471440..caabfcf6ac 100644
> --- a/libavformat/matroskadec.c
> +++ b/libavformat/matroskadec.c
> @@ -1256,13 +1256,23 @@ 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) {
Applied, thanks.
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