Re: [FFmpeg-devel] [RFC] Channels

["Tomas Härdin" <git@haerdin.se>]

fre 2024-03-22 klockan 03:25 +0100 skrev Michael Niedermayer:
> Hi all
> 
> we have code like
> st->codecpar->ch_layout.nb_channels = avio_rb32(pb);
> 
> and then somewhere there is some code that uses this by first
> allocating
> an array and that then hits OOM
> (it was this here:
>     map = av_calloc(nb_channels, sizeof(*channel_layout->u.map));)
> 
> is anyone against adding a max_channels field to AVFormatContext  or
> something
> like that ?

Sounds reasonable, but also we have FF_SANE_NB_CHANNELS as James said.
But a more proper solution is to use formal methods rather than
fuzzers. Proofs beat fuzzing every day

A more practical reason to limit channels is that there is without a
doubt oodles of overflow bugs that trigger with channels >= INT32_MAX
that don't trigger with channels == FF_SANE_NB_CHANNELS. Formal
verification would discovered these of course, but we have nowhere near
enough labour power to do that across the entire codebase. So limiting
channels is a practical way to ensure channels*bytes_per_sample and so
on can't overflow.

A second question is: which users would need two billion channels?

/Tomas
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