Re: random: /dev/random often returns short reads

[Denys Vlasenko]

On Wed, Jan 18, 2017 at 7:07 PM, Theodore Ts'o <tytso@xxxxxxx> wrote:
> In the ideal world, yes.  I've acknowledged this is a bug, in the "be
> conservative in what you send, liberal in what you receive" sense..
> But no one complained for three year, and userspace needs to be able
> to retry short reads instead of immediately erroring out.
>
> The problem is changing that code to figure out exactly how many bytes
> you need to get in order to have N random bytes is non-trivial.  So
> our choices are:
>
> 1) Transfer more bytes than might be needed to the secondary pool,
> which results in resource stranding --- since entropy in the secondary
> pool isn't available for reseeding the CRNG.  OTOH, given that we're
> now using the CRNG solution, and we're only reseeding every five
> minutes, I'm not actually all that worried about stranding some extra
> entropy bits in the blocking pool, since that's only going to happen
> if we have people *using* the /dev/random pool, and so that entropy
> will likely be used eventually anyway
...
...
> I'm leaning a bit towards 1 if we have to do something (which is my
> proposed, untested patch).

Thanks, this solution is okay for me.