Am Freitag, 5. Dezember 2014, 23:53:59 schrieb Herbert Xu:
Hi Herbert,
> On Wed, Dec 03, 2014 at 08:59:01PM +0100, Stephan Mueller wrote:
> > +static int rng_recvmsg(struct kiocb *unused, struct socket *sock,
> > + struct msghdr *msg, size_t len, int flags)
> > +{
> > + struct sock *sk = sock->sk;
> > + struct alg_sock *ask = alg_sk(sk);
> > + struct rng_ctx *ctx = ask->private;
> > + int err = -EFAULT;
> > +
> > + if (len == 0)
> > + return 0;
> > + if (len > MAXSIZE)
> > + len = MAXSIZE;
> > +
> > + lock_sock(sk);
>
> This lock simply protects ctx->result. Since you're using a
> tiny buffer why not just put it on the stack?
When I developed the DRBG code, I got comments that 128 byte variables shall
not be on the stack in kernel code.
But if you agree that I can put a 128 byte variable on the stack, I will see
it done.
>
> > + u8 *buf = kmalloc(seedsize, GFP_KERNEL);
> > + if (!buf)
> > + goto err;
> > + get_random_bytes(buf, seedsize);
> > + ret = crypto_rng_reset(private, buf, len);
>
> I think you should leave the seeding and the seed to the user.
> Perhaps do it through setsockopt (on the parent socket).
Sure. But please note that the seeding happens only when seedsize > 0. Such
seeding therefore is not performed for krng, and the DRBG because both seed
automatically.
Therefore, may I propose the following: We offer a setsockopt for (re)seeding.
For all RNGs with seedsize > 0, we return EAGAIN for recvmsg until a
setsockopt for at least seedsize is provided. That would imply that krng and
DRBG would be usable without seeding from user space.
--
Ciao
Stephan
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