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Date:   Wed, 23 Mar 2022 08:31:54 -0400
From:   "Theodore Ts'o" <tytso@mit.edu>
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Dominik Brodowski <linux@dominikbrodowski.net>,
        Jann Horn <jannh@google.com>
Subject: Re: [PATCH] random: allow writes to /dev/urandom to influence fast
 init
Message-ID: <YjsTOsqiNaURZQLM@mit.edu>
References: <20220322191436.110963-1-Jason@zx2c4.com>
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On Tue, Mar 22, 2022 at 10:00:49PM -0600, Jason A. Donenfeld wrote:
> 
> Another variation on that would be to do what this current patch does,
> but only crng_pre_init_inject() on CAP_SYS_ADMIN. But this has the same
> pitfall of only working as intended at cnrg_init=0 but not crng_init=1.
> That's better than nothing, but it's not perfect, and it introduces that
> problem with RNDADDTOENTCNT.

Well, one could argue that "RNDADDTOENTCNT" is a problem that has
always been there, and it already requires CAP_SYS_ADMIN.  So I'm not
sure it makes it any worse.

> > > And perhaps we might consider attempting to deprecate RNDADDTOENTCNT at
> > > some point in the future.
> >
> > That would be a good idea. ?:-)
> 
> Oh cool, I'm glad you agree. Let's do that then. Have a preferred path?
> Maybe just a pr_once() saying not to use it?

Probably.  We could get more aggressive (e.g., WARN), but the first
Google search on RNDADDTOENTCNT returned:

	https://github.com/jumpnow/rndaddtoentcnt

So I'm now regretting not silently making it vanish a decade or more ago...

       	   	      	  	   	     - Ted