Re: [PATCH] Use getentropy() for seeding PRNG

[Janne Blomqvist <blomqvist.janne@gmail.com>]

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On Fri, Aug 3, 2018 at 5:05 PM, Janne Blomqvist <blomqvist.janne@gmail.com>
wrote:

> On Fri, Aug 3, 2018 at 4:28 PM, Jakub Jelinek <jakub@redhat.com> wrote:
>
>> On Fri, Aug 03, 2018 at 04:19:03PM +0300, Janne Blomqvist wrote:
>> > --- a/libgfortran/intrinsics/random.c
>> > +++ b/libgfortran/intrinsics/random.c
>> > @@ -309,12 +309,9 @@ getosrandom (void *buf, size_t buflen)
>> >    for (size_t i = 0; i < buflen / sizeof (unsigned int); i++)
>> >      rand_s (&b[i]);
>> >    return buflen;
>> > +#elif defined(HAVE_GETENTROPY)
>> > +  return getentropy (buf, buflen);
>> >  #else
>>
>> I wonder if it wouldn't be better to use getentropy only if it is
>> successful
>> and fall back to whatever you were doing before.
>>
>> E.g. on Linux, I believe getentropy in glibc just uses the getrandom
>> syscall, which has only been introduced in Linux kernel 3.17.
>>
>
> Yes, that is my understanding as well.
>
>
>> So, if somebody is running glibc 2.25 or later on kernel < 3.17, it will
>> fail, even though reads from /dev/urandom could work.
>>
>
> Hmm, fair enough. So replace the random.c part of the patch with
>
> diff --git a/libgfortran/intrinsics/random.c b/libgfortran/intrinsics/
> random.c
> index 234c5ff95fd..229fa6995c0 100644
> --- a/libgfortran/intrinsics/random.c
> +++ b/libgfortran/intrinsics/random.c
> @@ -310,11 +310,10 @@ getosrandom (void *buf, size_t buflen)
>      rand_s (&b[i]);
>    return buflen;
>  #else
> -  /*
> -     TODO: When glibc adds a wrapper for the getrandom() system call
> -     on Linux, one could use that.
> -
> -     TODO: One could use getentropy() on OpenBSD.  */
> +#ifdef HAVE_GETENTROPY
> +  if (getentropy (buf, buflen) == 0)
> +    return 0;
> +#endif
>    int flags = O_RDONLY;
>  #ifdef O_CLOEXEC
>    flags |= O_CLOEXEC;
>
>
>
> Just to be sure, I regtested this slightly modified patch as well. Ok for
> trunk?
>
> --
> Janne Blomqvist
>



-- 
Janne Blomqvist