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

[Xiaohan Wang (王消寒)]

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: 9FF2128B147EF6730BADF133611EC787040B0FAB
>>>
>>> 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
>>>
>>>
>>
>
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