[FFmpeg-devel] [PATCH 2/2] configure: libbsd support for arc4random()

[Ganesh Ajjanagadde]

On Tue, Dec 8, 2015 at 8:16 AM, Clément Bœsch <u at pkh.me> wrote:
> On Tue, Dec 08, 2015 at 07:34:51AM -0500, Ganesh Ajjanagadde wrote:
>> On Tue, Dec 8, 2015 at 7:27 AM, wm4 <nfxjfg at googlemail.com> wrote:
>> > On Sun,  6 Dec 2015 22:56:33 -0500
>> > Ganesh Ajjanagadde <gajjanagadde at gmail.com> wrote:
>> >
>> >> On non-BSD machines, there exists a package libbsd for providing BSD
>> >> functionality. This can be used to get support for arc4random.
>> >>
>> >> Thus, an opt-in --enable-libbsd is added to configure for this
>> >> functionality.
>> >>
>> >> Tested on GNU/Linux.
>> >>
>> >
>> > This doesn't seem worth the trouble at all. Who is even going to use
>> > it, and why, and what additional hidden bugs will it cause?
>>
>> arc4random is a far superior interface, in that it can never fail. See
>> http://www.linuxfromscratch.org/hints/downloads/files/entropy.txt for
>> details.
>> As for hidden bugs, apart from configuration/detection issues, I see none.
>> If anything, it is easier to use /dev/urandom incorrectly.
>> Ultimately any code change is a tradeoff, with different people
>> feeling differently about various things.
>> I still feel that it is worth inclusion due to its technical merits.
>>
>
> Note that the behaviour of arc4random differs between implementations.
>
> http://insanecoding.blogspot.gr/2014/05/libressl-porting-update.html

That is for libressl, not libbsd, though the remark may still apply.
And there is no real fundamental issue: FFmpeg's seeding code anyway
varies between platforms, in the worst case using time.

Second, a getrandom system call has been added to the kernel, so
libbsd/libressl should upgrade to the new interface over time.

Whatever, if people don't want this, I will drop 2/2 but keep within
my own tree for a future date potentially.

1/2 is still very much worthwhile: platforms supporting natively
arc4random should use it (e.g the BSD's).

>
> --
> Clément B.
>
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