[FFmpeg-devel] [PATCH] Avoid undefined behavior by limiting PTS to 62 bits in ogg decoder

[Michael Niedermayer]

On Mon, Jul 30, 2018 at 01:31:59PM -0700, Fredrik Hubinette wrote:
> Not sure how to update the commit message.

git commit --amend


> The undefined behavior occurs in av_add_stable, which is called from
> compute_packet_fields.
> In that code PTS can be equal to -(1<<63), which then causes a int64_t to
> overflow.

This does not sound specific to oggdec. Thus a change in oggdec would likely
not fix it outside ogg.
Or am i missing something ?


thx

> 
> On Wed, Jul 18, 2018 at 4:04 AM Michael Niedermayer <michael at niedermayer.cc>
> wrote:
> 
> > On Mon, Jul 16, 2018 at 04:32:14PM -0700, Fredrik Hubinette wrote:
> > > With some (garbled) OGG data, PTS can overflow causing undefined
> > behavior.
> > > This patch avoids that by zeroing out PTS values greater than 2^62.
> >
> > >  oggdec.h |    3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > ff003b78842c7724ccc1a42f9584b1f8aa0b0b3d
> > 0001-Avoid-undefined-behavior-by-limiting-PTS-to-62-bits-.patch
> > > From 26a8582bc04f5bddc037ffcce99025e2f977abe0 Mon Sep 17 00:00:00 2001
> > > From: Fredrik Hubinette <hubbe at google.com>
> > > Date: Mon, 16 Jul 2018 14:54:43 -0700
> > > Subject: [PATCH] Avoid undefined behavior by limiting PTS to 62 bits in
> > ogg
> > >  decoder
> > >
> > > ---
> > >  libavformat/oggdec.h | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > I think someone reading this commit message would like to know more
> > about where that undefined behaviour occurs and how this is guranteeing
> > to fix it
> >
> >
> > [...]
> >
> > --
> > Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
> >
> > "Nothing to hide" only works if the folks in power share the values of
> > you and everyone you know entirely and always will -- Tom Scott
> >
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-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Its not that you shouldnt use gotos but rather that you should write
readable code and code with gotos often but not always is less readable
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