[FFmpeg-devel] [PATCH 1/2] avutil/random_seed: use arc4random() when available

[Ganesh Ajjanagadde]

On Thu, Dec 10, 2015 at 3:31 PM, Ganesh Ajjanagadde
<gajjanagadde at gmail.com> wrote:
> On Wed, Dec 9, 2015 at 8:08 AM, Ganesh Ajjanagadde
> <gajjanagadde at gmail.com> wrote:
>> On Sun, Dec 6, 2015 at 10:56 PM, Ganesh Ajjanagadde
>> <gajjanagadde at gmail.com> wrote:
>>> arc4random() was designed as a superior interface for system random
>>> number generation, designed for OpenBSD. It is thus an improvement to
>>> use it whenever available.
>>>
>>> As a side note, this may or may not get included in glibc, and there is
>>> a proposal to create a posix_random family based on these ideas:
>>> http://austingroupbugs.net/view.php?id=859.
>>>
>>> Untested as I lack OpenBSD.
>>>
>>> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
>>> ---
>>>  configure               | 2 ++
>>>  libavutil/random_seed.c | 4 ++++
>>>  2 files changed, 6 insertions(+)
>>>
>>> diff --git a/configure b/configure
>>> index 7530c88..e676269 100755
>>> --- a/configure
>>> +++ b/configure
>>> @@ -1840,6 +1840,7 @@ MATH_FUNCS="
>>>  SYSTEM_FUNCS="
>>>      access
>>>      aligned_malloc
>>> +    arc4random
>>>      clock_gettime
>>>      closesocket
>>>      CommandLineToArgvW
>>> @@ -5218,6 +5219,7 @@ check_func  ${malloc_prefix}memalign            && enable memalign
>>>  check_func  ${malloc_prefix}posix_memalign      && enable posix_memalign
>>>
>>>  check_func  access
>>> +check_func  arc4random
>>>  check_func_headers time.h clock_gettime || { check_func_headers time.h clock_gettime -lrt && add_extralibs -lrt && LIBRT="-lrt"; }
>>>  check_func  fcntl
>>>  check_func  fork
>>> diff --git a/libavutil/random_seed.c b/libavutil/random_seed.c
>>> index 8aa8c38..205a636 100644
>>> --- a/libavutil/random_seed.c
>>> +++ b/libavutil/random_seed.c
>>> @@ -121,6 +121,10 @@ uint32_t av_get_random_seed(void)
>>>      }
>>>  #endif
>>>
>>> +#if HAVE_ARC4RANDOM
>>> +    return arc4random();
>>> +#endif
>>> +
>>>      if (read_random(&seed, "/dev/urandom") == sizeof(seed))
>>>          return seed;
>>>      if (read_random(&seed, "/dev/random")  == sizeof(seed))
>>> --
>>> 2.6.3
>>>
>>
>> any objections to this: all objections so far have been for 2/2, i.e
>> for the more controversial one that harnesses libbsd for non-native
>> functionality?
>
> To clarify, none of wm4's comments apply here. It will provide
> benefits not just to OpenBSD, but also to other BSD's, Mac OS X, and
> some alternative libc's (not glibc, which refused and continues to
> refuse arc4random).
>
> @Ronald, or anyone else with a Mac: can you please try at least a build test?
>
> I have now shelved 2/2, as it has got drawn into a stalemate.

Going in tomorrow provided it works as intended when I test it on a
Mac and in the absence of comments.