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

[Xiaohan Wang (王消寒)]

+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: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> No great genius has ever existed without some touch of madness. --
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