Re: [FFmpeg-devel] [PATCH 2/2] avformat/id3v2: Check that decode_str() did advance

[Michael Niedermayer <michael@niedermayer.cc>]

[-- Attachment #1.1: Type: text/plain, Size: 8136 bytes --]

On Tue, Apr 15, 2025 at 12:17:32AM +0000, softworkz . wrote:
> 
> 
> > -----Original Message-----
> > From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of
> > Ridley Combs via ffmpeg-devel
> > Sent: Dienstag, 15. April 2025 02:03
> > To: ffmpeg-devel <ffmpeg-devel@ffmpeg.org>
> > Cc: Ridley Combs <rcombs@rcombs.me>
> > Subject: Re: [FFmpeg-devel] [PATCH 2/2] avformat/id3v2: Check that
> > decode_str() did advance
> > 
> > 
> > 
> > > On Apr 15, 2025, at 08:59, softworkz . <softworkz-at-
> > hotmail.com@ffmpeg.org> wrote:
> > >
> > >
> > >
> > >> -----Original Message-----
> > >> From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org <mailto:ffmpeg-
> > devel-bounces@ffmpeg.org>> On Behalf Of
> > >> Michael Niedermayer
> > >> Sent: Dienstag, 15. April 2025 01:20
> > >> To: FFmpeg development discussions and patches <ffmpeg-
> > >> devel@ffmpeg.org <mailto:devel@ffmpeg.org>>
> > >> Subject: Re: [FFmpeg-devel] [PATCH 2/2] avformat/id3v2: Check that
> > >> decode_str() did advance
> > >>
> > >> On Sat, Apr 12, 2025 at 01:49:53AM +0000, softworkz . wrote:
> > >>>
> > >>>
> > >>>> -----Original Message-----
> > >>>> From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of
> > >>>> Michael Niedermayer
> > >>>> Sent: Samstag, 12. April 2025 00:27
> > >>>> To: FFmpeg development discussions and patches <ffmpeg-
> > >> devel@ffmpeg.org>
> > >>>> Subject: [FFmpeg-devel] [PATCH 2/2] avformat/id3v2: Check that
> > >>>> decode_str() did advance
> > >>>>
> > >>>> Fixes infinite loop with unknown encodings
> > >>>>
> > >>>> We could alternatively error out from decode_str() or consume all
> > >> of
> > >>>> taglen
> > >>>> this would affect other callers though.
> > >>>>
> > >>>> Fixes: 409819224/clusterfuzz-testcase-minimized-
> > >> ffmpeg_dem_H261_fuzzer-
> > >>>> 6003527535362048
> > >>>> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > >>>> ---
> > >>>> libavformat/id3v2.c | 3 +++
> > >>>> 1 file changed, 3 insertions(+)
> > >>>>
> > >>>> diff --git a/libavformat/id3v2.c b/libavformat/id3v2.c
> > >>>> index 90314583a74..e3f7f9e2a90 100644
> > >>>> --- a/libavformat/id3v2.c
> > >>>> +++ b/libavformat/id3v2.c
> > >>>> @@ -341,10 +341,13 @@ static void read_ttag(AVFormatContext *s,
> > >>>> AVIOContext *pb, int taglen,
> > >>>>     taglen--; /* account for encoding type byte */
> > >>>>
> > >>>>     while (taglen > 1) {
> > >>>> +        int current_taglen = taglen;
> > >>>>         if (decode_str(s, pb, encoding, &dst, &taglen) < 0) {
> > >>>>             av_log(s, AV_LOG_ERROR, "Error reading frame %s,
> > >>>> skipped\n", key);
> > >>>>             return;
> > >>>>         }
> > >>>> +        if (current_taglen == taglen)
> > >>>> +            return;
> > >>>>
> > >>>>         count++;
> > >>>>
> > >>>> --
> > >>>> 2.49.0
> > >>>>
> > >>>> _______________________________________________
> > >>>
> > >>> Hi Michael,
> > >>>
> > >>> this kind of conflicts with this patch that I had submitted
> > >> recently:
> > >>>
> > >>>
> > >>
> > https://patchwork.ffmpeg.org/project/ffmpeg/patch/pull.54.ffstaging.FF
> > >> mpeg.1740873449247.ffmpegagent@gmail.com/
> > >>>
> > >>>
> > >>> I wonder whether my patch would still be prone to the issue your
> > >> patch is addressing -
> > >>
> > >> This already conflicts with rcombs patch in git master, i think
> > >> Applying: Fixes Trac ticket https://trac.ffmpeg.org/ticket/6949
> > >> Using index info to reconstruct a base tree...
> > >> M	libavformat/id3v2.c
> > >> Falling back to patching base and 3-way merge...
> > >> Auto-merging libavformat/id3v2.c
> > >> CONFLICT (content): Merge conflict in libavformat/id3v2.c
> > >> error: Failed to merge in the changes.
> > >> Patch failed at 0001 Fixes Trac ticket
> > >> https://trac.ffmpeg.org/ticket/6949
> > >>
> > >>
> > >>> do you have a test file perhaps?
> > >>
> > >> Will email you one, but the loop with a function that doesnt
> > advance
> > >> is an issue even if the specific file doesnt trigger it in a
> > different
> > >> implementation
> > >>
> > >> also probaly a good idea if you contact rcombs as you seemed to
> > work
> > >> on
> > >> the same code
> > >>
> > >> I was looking at teh ticket and saw a link to rcombs patch, looked
> > at
> > >> the patch and applied it. I did not realize there where 2 patches
> > >
> > >
> > > Hi Michael,
> > >
> > > I know the rcombs patch, but it has a - let's say - different
> > behavior.
> > > Let's look at an example where artist and genre have multiple
> > values:
> > >
> > >
> > > This was ffmpeg output unpatched:
> > >
> > >  Metadata:
> > >    title           : Infinite (Original Mix)
> > >    artist          : B-Front
> > >    track           : 1
> > >    album           : Infinite
> > >    date            : 2017
> > >    genre           : Hardstyle
> > >    TBPM            : 150
> > >    compilation     : 0
> > >    album_artist    : B-Front
> > >    publisher       : Roughstate
> > >
> > >
> > > This is what the rcombs patch does:
> > >
> > >  Metadata:
> > >    title           : Infinite (Original Mix)
> > >    artist          : B-Front
> > >    artist          : Second Artist Example
> > >    track           : 1
> > >    album           : Infinite
> > >    date            : 2017
> > >    genre           : Hardstyle
> > >    genre           : Test
> > >    genre           : Example
> > >    genre           : Hard Dance
> > >    TBPM            : 150
> > >    compilation     : 0
> > >    album_artist    : B-Front
> > >    publisher       : Roughstate
> > >
> > >
> > >
> > > My path does that:
> > >
> > >  Metadata:
> > >    title           : Infinite (Original Mix)
> > >    artist          : B-Front;Second Artist Example
> > >    track           : 1
> > >    album           : Infinite
> > >    date            : 2017
> > >    genre           : Hardstyle;Test;Example;Hard Dance
> > >    TBPM            : 150
> > >    compilation     : 0
> > >    album_artist    : B-Front
> > >    publisher       : Roughstate
> > >
> > >
> > >
> > > I'm not sure whether it is even allowed or intended that there are
> > > multiple metadata entries with the same key?
> > 
> > It is indeed an intended feature of the AVDictionary system, and the
> > metadata feature in particular.
> 
> Hi,
> 
> you meant to say that it is an intended change introduced by your patch? 😉 
> 
> Because we haven't had duplicate metadata keys before. I'm afraid but 
> I think these changes should be reverted, because it also creates invalid
> FFprobe output - like in case of JSON for example:
> 
> {
>     "format": {
>         "filename": "multiple_id3v2_4_values.mp3",
>         "nb_streams": 1,
>         "nb_programs": 0,
>         "nb_stream_groups": 0,
>         "format_name": "mp3",
>         "format_long_name": "MP2/3 (MPEG audio layer 2/3)",
>         "start_time": "0.011995",
>         "duration": "20.035918",
>         "size": "804936",
>         "bit_rate": "321397",
>         "probe_score": 51,
>         "tags": {
>             "title": "Infinite (Original Mix)",
>             "artist": "B-Front",
>             "artist": "Second Artist Example",
>             "track": "1",
>             "album": "Infinite",
>             "date": "2017",
>             "genre": "Hardstyle",
>             "genre": "Test",
>             "genre": "Example",
>             "genre": "Hard Dance",
>             "TBPM": "150",
>             "compilation": "0",
>             "album_artist": "B-Front",
>             "publisher": "Roughstate",
>             "encoder": "Lavf57.83.100",
>         }
>     }
> }

I think ffprobe should not generate invalid output if metadata given to it has
2 entries with the same key, independant of that being the correct way to export
metadata.

thx

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

Nations do behave wisely once they have exhausted all other alternatives. 
-- Abba Eban

[-- Attachment #1.2: signature.asc --]
[-- Type: application/pgp-signature, Size: 195 bytes --]

[-- Attachment #2: Type: text/plain, Size: 251 bytes --]

_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel

To unsubscribe, visit link above, or email
ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".