[FFmpeg-devel] [PATCH] matroskadec: fix NULL pointer dereference

[wm4]

On Sun, 16 Oct 2016 22:11:03 +0200
Andreas Cadhalpun <andreas.cadhalpun at googlemail.com> wrote:

> The problem was introduced in commit 1273bc6.
> 
> Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun at googlemail.com>
> ---
>  libavformat/matroskadec.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
> index 8847c62..a5d3c0e 100644
> --- a/libavformat/matroskadec.c
> +++ b/libavformat/matroskadec.c
> @@ -1759,7 +1759,7 @@ static int mkv_field_order(MatroskaDemuxContext *matroska, int64_t field_order)
>  
>      /* workaround a bug in our Matroska muxer, introduced in version 57.36 alongside
>       * this function, and fixed in 57.52 */
> -    if (sscanf(matroska->muxingapp, "Lavf%d.%d.%d", &major, &minor, &micro) == 3)
> +    if (matroska->muxingapp && sscanf(matroska->muxingapp, "Lavf%d.%d.%d", &major, &minor, &micro) == 3)
>          bttb = (major == 57 && minor >= 36 && minor <= 51 && micro >= 100);
>  
>      switch (field_order) {

Why do we even have this dumb check?

The files that have already produced will be misinterpreted by
compliant demuxers, and adding ugly workarounds is unfair to those
compliant demuxers.