[FFmpeg-devel] [PATCHv2] avformat/mp3dec, rmdec: check return value of ffio_ensure_seekback

[wm4]

On Tue, 5 Jan 2016 08:32:02 -0800
Ganesh Ajjanagadde <gajjanag at mit.edu> wrote:

> On Tue, Jan 5, 2016 at 5:29 AM, wm4 <nfxjfg at googlemail.com> wrote:
> > On Mon,  4 Jan 2016 17:50:01 -0800
> > Ganesh Ajjanagadde <gajjanagadde at gmail.com> wrote:
> >  
> >> ffio_ensure_seekback can fail due to e.g ENOMEM. This return value is
> >> checked here and a diagnostic is logged.
> >>
> >> All usage of ffio_ensure_seekback in the codebase now has the return value checked.
> >>
> >> Reviewed-by: wm4 <nfxjfg at googlemail.com>
> >> Reviewed-by: Ronald S. Bultje <rsbultje at gmail.com>
> >> Reviewed-by: Michael Niedermayer <michael at niedermayer.cc>
> >> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
> >> ---
> >>  libavformat/mp3dec.c | 13 +++++++++++--
> >>  libavformat/rmdec.c  |  3 ++-
> >>  2 files changed, 13 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/libavformat/mp3dec.c b/libavformat/mp3dec.c
> >> index c76b21e..57ebcc8 100644
> >> --- a/libavformat/mp3dec.c
> >> +++ b/libavformat/mp3dec.c
> >> @@ -372,11 +372,19 @@ static int mp3_read_header(AVFormatContext *s)
> >>          uint32_t header, header2;
> >>          int frame_size;
> >>          if (!(i&1023))
> >> -            ffio_ensure_seekback(s->pb, i + 1024 + 4);
> >> +            if ((ret = ffio_ensure_seekback(s->pb, i + 1024 + 4)) < 0) {
> >> +                av_log(s, AV_LOG_WARNING,
> >> +                       "initial junk detection and skipping impossible due to: %s\n", av_err2str(ret));
> >> +                goto skip_fail;
> >> +            }
> >>          frame_size = check(s->pb, off + i, &header);
> >>          if (frame_size > 0) {
> >>              avio_seek(s->pb, off, SEEK_SET);
> >> -            ffio_ensure_seekback(s->pb, i + 1024 + frame_size + 4);
> >> +            if ((ret = ffio_ensure_seekback(s->pb, i + 1024 + frame_size + 4)) < 0) {
> >> +                av_log(s, AV_LOG_WARNING,
> >> +                       "initial junk detection and skipping impossible due to: %s\n", av_err2str(ret));
> >> +                goto skip_fail;
> >> +            }
> >>              if (check(s->pb, off + i + frame_size, &header2) >= 0 &&
> >>                  (header & SAME_HEADER_MASK) == (header2 & SAME_HEADER_MASK))
> >>              {
> >> @@ -387,6 +395,7 @@ static int mp3_read_header(AVFormatContext *s)
> >>          }
> >>          avio_seek(s->pb, off, SEEK_SET);
> >>      }
> >> +skip_fail:
> >>
> >>      // the seek index is relative to the end of the xing vbr headers
> >>      for (i = 0; i < st->nb_index_entries; i++)
> >> diff --git a/libavformat/rmdec.c b/libavformat/rmdec.c
> >> index 4e46a3d..470e227 100644
> >> --- a/libavformat/rmdec.c
> >> +++ b/libavformat/rmdec.c
> >> @@ -618,7 +618,8 @@ static int rm_read_header(AVFormatContext *s)
> >>              size = avio_rb32(pb);
> >>              codec_pos = avio_tell(pb);
> >>
> >> -            ffio_ensure_seekback(pb, 4);
> >> +            if ((ret = ffio_ensure_seekback(pb, 4)) < 0)
> >> +                av_log(s, AV_LOG_WARNING, "seeking back impossible due to: %s\n", av_err2str(ret));
> >>              v = avio_rb32(pb);
> >>              if (v == MKBETAG('M', 'L', 'T', 'I')) {
> >>                  ret = rm_read_multi(s, s->pb, st, mime);  
> >
> > I maintain that this should not be done, because it makes the code
> > verbose for no reason.  
> 
> Michael has pointed out that when seekback fails, one should really
> break out of the junk detection loop in mp3dec. Your idea fails to
> achieve it.

Why? It's not really harmful. You could even argue that this will make
the common case (skipping jumk and finding a valid frame in a seekable
file) work in low memory situations, while your patch breaks it.