Re: [PATCH 10/18] crypto: dh - introduce support for ephemeral key generation to dh-generic

["Stephan Müller" <smueller@chronox.de>]

Am Mittwoch, 1. Dezember 2021, 01:48:50 CET schrieb Nicolai Stange:

Hi Nicolai,

> The support for NVME in-band authentication currently in the works ([1])
> needs to generate ephemeral DH keys. Make dh-generic's ->set_secret()
> to generate an ephemeral key via the recently added crypto_dh_gen_privkey()
> in case the input ->key_size is zero. Note that this behaviour is in
> analogy to ecdh's ->set_secret().
> 
> [1] https://lkml.kernel.org/r/20211122074727.25988-4-hare@suse.de
> 
> Signed-off-by: Nicolai Stange <nstange@suse.de>
> ---
>  crypto/dh.c | 24 ++++++++++++++++++++----
>  1 file changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/crypto/dh.c b/crypto/dh.c
> index 131b80064cb1..2e49b114e038 100644
> --- a/crypto/dh.c
> +++ b/crypto/dh.c
> @@ -71,25 +71,41 @@ static int dh_set_secret(struct crypto_kpp *tfm, const
> void *buf, {
>  	struct dh_ctx *ctx = dh_get_ctx(tfm);
>  	struct dh params;
> +	char key[CRYPTO_DH_MAX_PRIVKEY_SIZE];
> +	int err;
> 
>  	/* Free the old MPI key if any */
>  	dh_clear_ctx(ctx);
> 
> -	if (crypto_dh_decode_key(buf, len, &params) < 0)
> +	err = crypto_dh_decode_key(buf, len, &params);
> +	if (err)
>  		goto err_clear_ctx;
> 
> -	if (dh_set_params(ctx, &params) < 0)
> +	if (!params.key_size) {

As this params data may come from user space, shouldn't we use the same logic 
as in ecdh's set_key function:

if (!params.key || !params.key_size)

?


> +		err = crypto_dh_gen_privkey(params.group_id, key,
> +					    &params.key_size);
> +		if (err)
> +			goto err_clear_ctx;
> +		params.key = key;
> +	}
> +
> +	err = dh_set_params(ctx, &params);
> +	if (err)
>  		goto err_clear_ctx;
> 
>  	ctx->xa = mpi_read_raw_data(params.key, params.key_size);
> -	if (!ctx->xa)
> +	if (!ctx->xa) {
> +		err = -EINVAL;
>  		goto err_clear_ctx;
> +	}
> +
> +	memzero_explicit(key, sizeof(key));
> 
>  	return 0;
> 
>  err_clear_ctx:
>  	dh_clear_ctx(ctx);
> -	return -EINVAL;
> +	return err;
>  }
> 
>  /*


Ciao
Stephan