[PATCH 02/12] random: Implement read_random via getentropy.

[Christian Mauderer]

Am 01.08.2018 um 16:28 schrieb Gedare Bloom:
> Is this relied on for IPSec? How secure is it?

Hello Gedare,

the IPSec implementation in FreeBSD and therefore in RTEMS too uses that
function. So you are right that it is a critical one for security.

`read_random` is a low-level FreeBSD random number function. From the
man page (see
https://www.freebsd.org/cgi/man.cgi?query=read_random&manpath=FreeBSD+11.2-RELEASE+and+Ports):

    The read_random() function is used to return entropy directly from
    the entropy device if it has been loaded. If the entropy device is
    not loaded, then the buffer is ignored and zero is returned. The
    buffer is filled with no more than count bytes. It is strongly
    advised that read_random() is not used; instead use arc4rand()
    unless it is necessary to know that no entropy has been returned.

That's basically the same what our `getentropy` does. Returning entropy
directly from the entropy device if it is available. So it is as close
to the original behavior as we can get.

Of course `getentropy` only returns a good entropy if there is a real
entropy source in the BSP. Currently that is only true for the atsam
BSP. I think there should be a patch for BBB somewhere on the mailing list.

We have a chapter in the BSP guide regarding that:

    https://docs.rtems.org/branches/master/bsp-howto/getentropy.html

There is also a hint that a good entropy source is necessary for
cryptographic applications. It would be great if you have a good idea
how to make a user aware of the security problem if he doesn't use a
good crypto source.

Best regards

Christian

> 
> On Wed, Aug 1, 2018 at 4:04 AM, Christian Mauderer
> <christian.mauderer at embedded-brains.de> wrote:
>> ---
>>  freebsd/sys/sys/random.h | 10 ++++++++++
>>  1 file changed, 10 insertions(+)
>>
>> diff --git a/freebsd/sys/sys/random.h b/freebsd/sys/sys/random.h
>> index 396ec2b1..996ca5c1 100644
>> --- a/freebsd/sys/sys/random.h
>> +++ b/freebsd/sys/sys/random.h
>> @@ -50,11 +50,21 @@ read_random_uio(void *a __unused, u_int b __unused)
>>  {
>>         return (0);
>>  }
>> +#ifndef __rtems__
>>  static __inline u_int
>>  read_random(void *a __unused, u_int b __unused)
>>  {
>>         return (0);
>>  }
>> +#else /* __rtems__ */
>> +#include <unistd.h>
>> +static __inline u_int
>> +read_random(void *ptr, u_int n)
>> +{
>> +       getentropy(ptr, n);
>> +       return (n);
>> +}
>> +#endif /* __rtems__ */
>>  #endif
>>
>>  /*
>> --
>> 2.13.7
>>
>> _______________________________________________
>> devel mailing list
>> devel at rtems.org
>> http://lists.rtems.org/mailman/listinfo/devel

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