Re: [FFmpeg-devel] [PATCH 1/3] avformat/dashdec: fail on probing non mpd file extension

[Michael Niedermayer <michael@niedermayer.cc>]

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On Mon, May 08, 2023 at 04:05:40PM +0200, Tobias Rapp wrote:
> On 08/05/2023 14:00, James Almer wrote:
> 
> > On 5/6/2023 10:25 AM, Michael Niedermayer wrote:
> > > Its unexpected that a .avi or other "standard" file turns into a
> > > playlist.
> > > The goal of this patch is to avoid this unexpected behavior and possible
> > > privacy or security differences.
> > > 
> > > This is similar to the same change to hls
> > > 
> > > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > > ---
> > >   libavformat/dashdec.c | 11 +++++++----
> > >   1 file changed, 7 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/libavformat/dashdec.c b/libavformat/dashdec.c
> > > index 29d4680c68..294e14150d 100644
> > > --- a/libavformat/dashdec.c
> > > +++ b/libavformat/dashdec.c
> > > @@ -2336,10 +2336,13 @@ static int dash_probe(const AVProbeData *p)
> > >           av_stristr(p->buf, "dash:profile:isoff-live:2011") ||
> > >           av_stristr(p->buf, "dash:profile:isoff-live:2012") ||
> > >           av_stristr(p->buf, "dash:profile:isoff-main:2011") ||
> > > -        av_stristr(p->buf, "3GPP:PSS:profile:DASH1")) {
> > > -        return AVPROBE_SCORE_MAX;
> > > -    }
> > > -    if (av_stristr(p->buf, "dash:profile")) {
> > > +        av_stristr(p->buf, "3GPP:PSS:profile:DASH1") ||
> > > +        av_stristr(p->buf, "dash:profile")) {
> > > +        if (!av_match_ext(p->filename, "mpd")) {
> > > +            av_log(NULL, AV_LOG_ERROR, "Not detecting dash with non
> > > standard extension\n");
> > > +            return 0;
> > > +        }
> > > +
> > >           return AVPROBE_SCORE_MAX;
> > >       }
> > 
> > Failing because it didn't match an extensions sort of goes against the
> > point of probing, which even has a low score return value that's
> > basically "it matched extension" as a sort of last resort.
> > 
> > I'd say wrap this in a FF_COMPLIANCE_STRICT check (since i assume the
> > spec does state mpd must be the extension), but i think we have no
> > access to the AVFormatContext here?
> 
> DASH is usually transferred over HTTP where file extensions are of minor
> interest, the relevant type information is in the Mime-Type header.

would anyone be opposed to return 0 from dash_probe() when
both the mime_type and the extension are wrong ?

Here both the server says its not dash as well as the extension not being the
standard for dash

example: a crafted image.jpeg uploaded somewhere is played as dash.
or am i missing something that would stop that ?

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Never trust a computer, one day, it may think you are the virus. -- Compn

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