[FFmpeg-devel] [PATCH 1/2] avutil: Add Simple loop detector

[Michael Niedermayer]

On Thu, Aug 08, 2019 at 03:38:58PM +0100, Kieran Kunhya wrote:
> >
> > You argue that it does not NEED to be in lavu, but not that it SHOULD
> > note.
> >
> > > Plus, its not really common av code, and don't let its name mislead
> > > you, its more of a hack.
> >
> > I will disregard the insulting subtext of this sentence.
> >
> 
> There is nothing insulting about this sentence. IMO this is a hack, how
> come we have not needed such a thing for years?

we didnt "need" the bugfixes because the code was buggy.

The "building block" of a offset or pointer pointing anywhere in a file
is common, that can lead to cycles. Maybe the fuzzers are not good at
creating such constructs out of thin air but i wouldnt use this as
argument that the code isnt containing such bugs

PS: the reason why fuzzers fail to find such loops is likely because 
its not locally convergent. A pointer closing a loop will not run more
iterations as it become closer in value to closing the loop. It doesnt
loop and only in maybe 1 out of 4 billion values will infinite loop and
that only if all surrounding data structures also are valid enough.

Thanks

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety -- Benjamin Franklin
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