Re: [PATCH 3/8] random: trigger random_ready callback upon crng_init == 1

[Stephan Müller]

Am Dienstag, 17. Januar 2017, 23:12:50 CET schrieb Theodore Ts'o:

Hi Theodore,

> On Tue, Dec 27, 2016 at 11:39:57PM +0100, Stephan Müller wrote:
> > The random_ready callback mechanism is intended to replicate the
> > getrandom system call behavior to in-kernel users. As the getrandom
> > system call unblocks with crng_init == 1, trigger the random_ready
> > wakeup call at the same time.
> 
> It was deliberate that random_ready would only get triggered with
> crng_init==2.
> 
> In general I'm assuming kernel callers really want real randomness (as
> opposed to using prandom), where as there's a lot of b.s. userspace
> users of kernel randomness (for things that really don't require
> cryptographic randomness, e.g., for salting Python dictionaries,
> systemd/udev using /dev/urandom for non-cryptographic, non-security
> applications etc.)

Users of getrandom want to ensure that they get random data from a DRNG that 
is seeded, just like in-kernel users may want if they choose the callback-
approach.

I do not understand why there should be different treatment of in-kernel vs 
user space callers in that respect.

(And yes, I do not want to open a discussion whether crng_init==1 can 
considered as a sufficiently seeded DRNG as such discussion will lead 
nowhere.)

Ciao
Stephan
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Re: [PATCH 3/8] random: trigger random_ready callback upon crng_init == 1

[Theodore Ts'o]

On Tue, Dec 27, 2016 at 11:39:57PM +0100, Stephan Müller wrote:
> The random_ready callback mechanism is intended to replicate the
> getrandom system call behavior to in-kernel users. As the getrandom
> system call unblocks with crng_init == 1, trigger the random_ready
> wakeup call at the same time.

It was deliberate that random_ready would only get triggered with
crng_init==2.

In general I'm assuming kernel callers really want real randomness (as
opposed to using prandom), where as there's a lot of b.s. userspace
users of kernel randomness (for things that really don't require
cryptographic randomness, e.g., for salting Python dictionaries,
systemd/udev using /dev/urandom for non-cryptographic, non-security
applications etc.)

- Ted
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[PATCH 3/8] random: trigger random_ready callback upon crng_init == 1

[Stephan Müller]

The random_ready callback mechanism is intended to replicate the
getrandom system call behavior to in-kernel users. As the getrandom
system call unblocks with crng_init == 1, trigger the random_ready
wakeup call at the same time.

Signed-off-by: Stephan Mueller 
---
 drivers/char/random.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 482531d..5c26b1c 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -810,6 +810,7 @@ static int crng_fast_load(const char *cp, size_t len)
}
if (crng_init_cnt >= CRNG_INIT_CNT_THRESH) {
crng_init = 1;
+   process_random_ready_list();
wake_up_interruptible(_init_wait);
pr_notice("random: fast init done\n");
}
-- 
2.9.3


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