[FFmpeg-devel] Fix memset size on ctts_data in mov_read_trun()

[Xiaohan Wang (王消寒)]

Thanks! Updated the patch. Please take a look again.

On Sat, Feb 24, 2018 at 7:04 PM, Michael Niedermayer <michael at niedermayer.cc
> wrote:

> On Fri, Feb 23, 2018 at 05:12:05PM -0800, Xiaohan Wang (王消寒) wrote:
> > Michael: Dale and I dig into history a bit more and we don't understand
> why
> > the code is changed to the current state around memset. This new patch
> > reverted the change back to the previous state which we felt is much
> > cleaner. Please see the CL description for details and take a look at the
> > new patch. Thanks!
> >
> > On Wed, Feb 21, 2018 at 1:14 PM, Xiaohan Wang (王消寒) <xhwang at chromium.org
> >
> > wrote:
> >
> > > jstebbins: kindly ping!
> > >
> > > On Fri, Feb 16, 2018 at 2:42 PM, Xiaohan Wang (王消寒) <
> xhwang at chromium.org>
> > > wrote:
> > >
> > >> +jstebbins@ who wrote that code.
> > >>
> > >> On Fri, Feb 16, 2018 at 12:30 PM, Michael Niedermayer <
> > >> michael at niedermayer.cc> wrote:
> > >>
> > >>> On Thu, Feb 15, 2018 at 12:10:33PM -0800, Xiaohan Wang (王消寒) wrote:
> > >>> >
> > >>>
> > >>> >  mov.c |    3 ++-
> > >>> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >>> > 5597d0b095f8b15eb11503010a51c2bc2c022413
> > >>> 0001-ffmpeg-Fix-memset-size-on-ctts_data-in-mov_read_trun.patch
> > >>> > From 7c1e6b50ebe35b2a38c4f1d0a988e31eccbd0ead Mon Sep 17 00:00:00
> 2001
> > >>> > From: Xiaohan Wang <xhwang at chromium.org>
> > >>> > Date: Thu, 15 Feb 2018 12:05:53 -0800
> > >>> > Subject: [PATCH] ffmpeg: Fix memset size on ctts_data in
> > >>> mov_read_trun()
> > >>> >
> > >>> > The allocated size of sc->ctts_data is
> > >>> > (st->nb_index_entries + entries) * sizeof(*sc->ctts_data).
> > >>> >
> > >>> > The size to memset at offset sc->ctts_data + sc->ctts_count should
> be
> > >>> > (st->nb_index_entries + entries - sc->ctts_count) *
> > >>> sizeof(*sc->ctts_data))
> > >>> >
> > >>> > The current code missed |entries| I believe.
> > >>>
> > >>> shouldnt "entries" be read by this function later and so shouldnt
> need a
> > >>> memset?
> > >>> I didnt write this, but it looks a bit to me as if it was intended to
> > >>> only
> > >>> clear the area that would not be read later
> > >>>
> > >>
> > >> I thought we only had sc->ctts_count entries before av_fast_realloc,
> so
> > >> memset everything starting from sc->ctts_data + sc->ctts_count
> couldn't
> > >> go wrong. But I am not familiar with this code and that could totally
> be
> > >> wrong. I added jstebbins@ who wrote the code and hopefully we can get
> > >> expert opinion there.
> > >>
> > >>
> > >>> [...]
> > >>> --
> > >>> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC7
> 87040B0FAB
> > >>>
> > >>> No great genius has ever existed without some touch of madness. --
> > >>> Aristotle
> > >>>
> > >>> _______________________________________________
> > >>> ffmpeg-devel mailing list
> > >>> ffmpeg-devel at ffmpeg.org
> > >>> http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
> > >>>
> > >>>
> > >>
> > >
>
> >  mov.c |    5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> > e5bbe55f0b1260f787f431b5c45e6ca49a7d2d1e  0001-Fix-memset-size-on-ctts_
> data-in-mov_read_trun-round-.patch
> > From f34b35ec5749c17b21f80665a0b8859bce3e84ab Mon Sep 17 00:00:00 2001
> > From: Xiaohan Wang <xhwang at chromium.org>
> > Date: Fri, 23 Feb 2018 10:51:30 -0800
> > Subject: [PATCH] Fix memset size on ctts_data in mov_read_trun() (round
> 2)
> >
> > The allocated size of sc->ctts_data is
> > (st->nb_index_entries + entries) * sizeof(*sc->ctts_data).
> >
> > The size to memset at offset sc->ctts_data + sc->ctts_count should be
> > (st->nb_index_entries + entries - sc->ctts_count) *
> > sizeof(*sc->ctts_data))
> >
> > The current code missed |entries| I believe, which was introduced in
> > https://patchwork.ffmpeg.org/patch/5541/.
> >
> > However, after offline discussion, it seems the original code is much
> > more clear to read (before https://patchwork.ffmpeg.org/patch/5541/).
> >
> > Hence this CL revert the memset logic to it's previous state by
> > remembering the |old_ctts_allocated_size|, and only memset the newly
> > allocated entries.
> > ---
> >  libavformat/mov.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/libavformat/mov.c b/libavformat/mov.c
> > index a3725692a7..f8d79c7b02 100644
> > --- a/libavformat/mov.c
> > +++ b/libavformat/mov.c
> > @@ -4713,6 +4713,7 @@ static int mov_read_trun(MOVContext *c,
> AVIOContext *pb, MOVAtom atom)
> >      st->index_entries= new_entries;
> >
> >      requested_size = (st->nb_index_entries + entries) *
> sizeof(*sc->ctts_data);
> > +    unsigned int old_ctts_allocated_size = sc->ctts_allocated_size;
>
> this should possibly be size_t
>
> and declaration and statements should not be mixed
>
> libavformat/mov.c: In function ‘mov_read_trun’:
> libavformat/mov.c:4691:5: warning: ISO C90 forbids mixed declarations and
> code [-Wdeclaration-after-statement]
>
> [...]
>
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> If you fake or manipulate statistics in a paper in physics you will never
> get a job again.
> If you fake or manipulate statistics in a paper in medicin you will get
> a job for life at the pharma industry.
>
> _______________________________________________
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> ffmpeg-devel at ffmpeg.org
> http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>
>
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