[FFmpeg-devel] [PATCH] add av_enable_strict_whitelists()

[Nicolas George]

Le quartidi 4 brumaire, an CCXXIII, Michael Niedermayer a écrit :
> This fixes the issue that a not set or not forwarded whitelist
> would allow to bypass it.

I am a bit worried by the sheer amount of extra code and API this simple
feature requires. Maybe it is a sign that it was not the best approach to
begin with.

Also, I did not say at the time, but I believe using a string to hold a list
like that is quite ugly.

Unless I am mistaken, the core of the problem resides in the existence of
global variables in the library, and this is not the only instance of this
issue: remember people who want to free the global mutex manager, not
understanding that "still reachable" is not a memory leak.

There is an idea that I have been nursing for some time: moving all these
global variables to a structure, and start passing it around everywhere.
Most of the functions that access the global variables already have some
kind of context where the pointer can be stored, so it would only require
changing a few API entry points.

That may look somewhat like that:

AVCodecInstance *libavcodec = avcodec_library_create(OPTIONS);
AVFormatInstance *libavformat = avformat_library_create(libavformat, OPTIONS);

avformat_instance_open_input(libavformat, &ctx, filename, NULL, NULL);

Then the whitelist feature comes for free: use the options to disable
registering all the codecs, then manually register the ones needed.

Of course, for compatibility, a global instance need to be inited if the
legacy entry points are used, but it becomes much easier to test extensively
that modern API usage will not touch them.

Of course, that requires more work, and the whitelist feature will not be
available immediately, but in the long run I believe it would be greatly
beneficial.

What do people think of that?

Regards,

-- 
  Nicolas George
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