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

[Tobias Rapp <t.rapp@noa-archive.com>]

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.

I think we already have the "format_whitelist" API for applications that 
want to restrict the list of formats when loading a file from untrusted 
sources?

Regards, Tobias

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