[FFmpeg-devel] [PATCH] Make av_get_random_seed not block when waiting for more entropy

Måns Rullgård mans
Wed Jun 30 18:19:05 CEST 2010

Martin Storsj? <martin at martin.st> writes:

> On Wed, 30 Jun 2010, Michael Niedermayer wrote:
>> before you spend more time on this.
>> There is a possible security issue with using non block mode
>> namely if we have /dev/*random and not use it we can end up
>> using a uninitialized variable. Thats an information leak
>> it could leak from pointers (kills ASLR) to OS/platform or
>> compiler version or or or ...
>> thats all usefull information for a attacker
>> he only has to saturate /dev/random so it would block
> Could you elaborate on your concern here? The fix he committed tries
> both /dev/random and /dev/urandom, and the latter should never block
> (afaik), and even in that case I don't see where any uninitialized
> variable would be leaked?

If neither of the files exist, or only /dev/random exists and blocks,
it will return an uninitialised value.  It changes only on systems
that have a blocking /dev/random and no /dev/urandom.

M?ns Rullg?rd
mans at mansr.com

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