On Tue, 5 Jan 2016 08:32:02 -0800
Ganesh Ajjanagadde <gajja...@mit.edu> wrote:
> On Tue, Jan 5, 2016 at 5:29 AM, wm4 <nfx...@googlemail.com> wrote:
> > On Mon, 4 Jan 2016 17:50:01 -0800
> > Ganesh Ajjanagadde <gajjanaga...@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 <nfx...@googlemail.com>
> >> Reviewed-by: Ronald S. Bultje <rsbul...@gmail.com>
> >> Reviewed-by: Michael Niedermayer <mich...@niedermayer.cc>
> >> Signed-off-by: Ganesh Ajjanagadde <gajjanaga...@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.
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