[FFmpeg-devel] [PATCH 3/4] avutil/frame: Reimplement av_frame_new_side_data() without size=0 special case

[wm4]

On Thu, 23 Feb 2017 17:12:35 +0100
Michael Niedermayer <michael at niedermayer.cc> wrote:

> On Thu, Feb 23, 2017 at 03:26:22PM +0100, wm4 wrote:
> > On Thu, 23 Feb 2017 15:19:31 +0100
> > Michael Niedermayer <michael at niedermayer.cc> wrote:
> >   
> > > The size 0 special case causes side data to be created which is
> > > different and a special case if for any reasons size = 0 is passed
> > > 
> > > Fixes: multiple runtime error: null pointer passed as argument 1, which is declared to never be null
> > > Fixes: 653/clusterfuzz-testcase-5773837415219200
> > > 
> > > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg
> > > 
> > > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> > > ---
> > >  libavutil/frame.c | 55 +++++++++++++++++++++++++++++--------------------------
> > >  1 file changed, 29 insertions(+), 26 deletions(-)
> > > 
> > > diff --git a/libavutil/frame.c b/libavutil/frame.c
> > > index 2913982e91..8811dcdcfe 100644
> > > --- a/libavutil/frame.c
> > > +++ b/libavutil/frame.c
> > > @@ -26,6 +26,11 @@
> > >  #include "mem.h"
> > >  #include "samplefmt.h"
> > >  
> > > +
> > > +static AVFrameSideData *frame_new_side_data(AVFrame *frame,
> > > +                                            enum AVFrameSideDataType type,
> > > +                                            AVBufferRef *buf);
> > > +
> > >  MAKE_ACCESSORS(AVFrame, frame, int64_t, best_effort_timestamp)
> > >  MAKE_ACCESSORS(AVFrame, frame, int64_t, pkt_duration)
> > >  MAKE_ACCESSORS(AVFrame, frame, int64_t, pkt_pos)
> > > @@ -344,20 +349,11 @@ FF_ENABLE_DEPRECATION_WARNINGS
> > >              }
> > >              memcpy(sd_dst->data, sd_src->data, sd_src->size);
> > >          } else {
> > > -            sd_dst = av_frame_new_side_data(dst, sd_src->type, 0);
> > > +            sd_dst = frame_new_side_data(dst, sd_src->type, av_buffer_ref(sd_src->buf));
> > >              if (!sd_dst) {
> > >                  wipe_side_data(dst);
> > >                  return AVERROR(ENOMEM);
> > >              }
> > > -            if (sd_src->buf) {
> > > -                sd_dst->buf = av_buffer_ref(sd_src->buf);
> > > -                if (!sd_dst->buf) {
> > > -                    wipe_side_data(dst);
> > > -                    return AVERROR(ENOMEM);
> > > -                }
> > > -                sd_dst->data = sd_dst->buf->data;
> > > -                sd_dst->size = sd_dst->buf->size;
> > > -            }
> > >          }
> > >          av_dict_copy(&sd_dst->metadata, sd_src->metadata, 0);
> > >      }
> > > @@ -633,40 +629,47 @@ AVBufferRef *av_frame_get_plane_buffer(AVFrame *frame, int plane)
> > >      return NULL;
> > >  }
> > >  
> > > -AVFrameSideData *av_frame_new_side_data(AVFrame *frame,
> > > -                                        enum AVFrameSideDataType type,
> > > -                                        int size)
> > > +static AVFrameSideData *frame_new_side_data(AVFrame *frame,
> > > +                                            enum AVFrameSideDataType type,
> > > +                                            AVBufferRef *buf)
> > >  {
> > >      AVFrameSideData *ret, **tmp;
> > >  
> > > -    if (frame->nb_side_data > INT_MAX / sizeof(*frame->side_data) - 1)
> > > +    if (!buf)
> > >          return NULL;
> > >  
> > > +    if (frame->nb_side_data > INT_MAX / sizeof(*frame->side_data) - 1)
> > > +        goto fail;
> > > +
> > >      tmp = av_realloc(frame->side_data,
> > >                       (frame->nb_side_data + 1) * sizeof(*frame->side_data));
> > >      if (!tmp)
> > > -        return NULL;
> > > +        goto fail;
> > >      frame->side_data = tmp;
> > >  
> > >      ret = av_mallocz(sizeof(*ret));
> > >      if (!ret)
> > > -        return NULL;
> > > -
> > > -    if (size > 0) {
> > > -        ret->buf = av_buffer_alloc(size);
> > > -        if (!ret->buf) {
> > > -            av_freep(&ret);
> > > -            return NULL;
> > > -        }
> > > +        goto fail;
> > >  
> > > -        ret->data = ret->buf->data;
> > > -        ret->size = size;
> > > -    }
> > > +    ret->buf = buf;
> > > +    ret->data = ret->buf->data;
> > > +    ret->size = buf->size;
> > >      ret->type = type;
> > >  
> > >      frame->side_data[frame->nb_side_data++] = ret;
> > >  
> > >      return ret;
> > > +fail:
> > > +    av_buffer_unref(&buf);
> > > +    return NULL;
> > > +}
> > > +
> > > +AVFrameSideData *av_frame_new_side_data(AVFrame *frame,
> > > +                                        enum AVFrameSideDataType type,
> > > +                                        int size)
> > > +{
> > > +
> > > +    return frame_new_side_data(frame, type, av_buffer_alloc(size));
> > >  }
> > >  
> > >  AVFrameSideData *av_frame_get_side_data(const AVFrame *frame,  
> > 
> > Why not restore Libav's version, which doesn't seem to need all this?  
> 
> it would remove optimizations and who knows what else. Also iam
> interrested in fixing security and undefined behavor issues in FFmpeg.
> The code in FFmpeg has been extensivly tested within FFmpeg and
> simply throwing it out and replacing it by something else would
> bring us to code that has not been tested in FFmpeg.

Actually it looks like the Libav version doesn't even have this
per side-data buffer ref, which makes it so different.

I'm not sure what's the actual problem here. If size==0, then data can
be NULL just fine? If something accesses data anyway (even if size==0),
that should probably be fixed instead.

In general it feels like the change makes the new code slightly
trickier than necessary (and the forward declaration looks ugly), but
feel free to ignore me.