[PATCH] Use arc4random() to permutate talloc_magic number

[Andrew Bartlett]

On Wed, 2018-02-14 at 03:59 +0100, Timur I. Bakeyev via samba-technical 
wrote:
> Hi!
> 
> I've noticed that talloc testsuite fails on FreeBSD cause talloc_magic is
> always a predictable number, derived from the function address of the
> loaded library, which is unfortunately always the same(contrary to OpenBSD,
> for example). The existing talloc code uses Linux/glibc specific calls to
> obtaining random bytes to permutate talloc_magic. *BSD has their own set of
> arc4*  functions that can provide cryptographically applicable PRNG.
> 
> So, this small patch adds support for the usage of arc4random() to obtain
> random talloc_magic signature per invocation.

The problem I have with this being the default is that unlike on *BSD
arc4random on in libbsd relies on the recent getentropy() stuff or goes
back to /dev/urandom.  

Now, you don't link against libbsd intentionally, but I can see that
happening. 

I chose the getauxval() because we don't want the library constructor
for talloc looking to open files.

Sorry,

Andrew Bartlett

-- 
Andrew Bartlett
https://samba.org/~abartlet/
Authentication Developer, Samba Team         https://samba.org
Samba Development and Support, Catalyst IT   
https://catalyst.net.nz/services/samba