Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Nicolai Stange <nstange@suse.de>
To:     Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>
Cc:     =?UTF-8?q?Stephan=20M=C3=BCller?= <smueller@chronox.de>,
        Hannes Reinecke <hare@suse.de>, Torsten Duwe <duwe@suse.de>,
        David Howells <dhowells@redhat.com>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org,
        keyrings@vger.kernel.org, Nicolai Stange <nstange@suse.de>
Subject: [PATCH v4 11/15] crypto: dh - allow for passing NULL to the ffdheXYZ(dh)s' ->set_secret()
Date:   Mon, 21 Feb 2022 13:10:57 +0100
Message-Id: <20220221121101.1615-12-nstange@suse.de>
In-Reply-To: <20220221121101.1615-1-nstange@suse.de>
References: <20220221121101.1615-1-nstange@suse.de>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Ephemeral key generation can be requested from any of the ffdheXYZ(dh)
variants' common ->set_secret() by passing it an (encoded) struct dh
with the key parameter being unset, i.e. with ->key_size == 0. As the
whole purpose of the ffdheXYZ(dh) templates is to fill in the group
parameters as appropriate, they expect ->p and ->g to be unset in any
input struct dh as well. This means that a user would have to encode an
all-zeroes struct dh instance via crypto_dh_encode_key() when requesting
ephemeral key generation from a ffdheXYZ(dh) instance, which is kind of
pointless.

Make dh_safe_prime_set_secret() to decode a struct dh from the supplied
buffer only if the latter is non-NULL and initialize it with all zeroes
otherwise.

That is, it is now possible to call

  crypto_kpp_set_secret(tfm, NULL, 0);

on any ffdheXYZ(dh) tfm for requesting ephemeral key generation.

Signed-off-by: Nicolai Stange <nstange@suse.de>
---
 crypto/dh.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/crypto/dh.c b/crypto/dh.c
index 869a0476e5e2..d0d24f615b2d 100644
--- a/crypto/dh.c
+++ b/crypto/dh.c
@@ -444,17 +444,18 @@ static int dh_safe_prime_set_secret(struct crypto_kpp *tfm, const void *buffer,
 	struct dh_safe_prime_instance_ctx *inst_ctx =
 		dh_safe_prime_instance_ctx(tfm);
 	struct dh_safe_prime_tfm_ctx *tfm_ctx = kpp_tfm_ctx(tfm);
-	struct dh params;
+	struct dh params = {};
 	void *buf = NULL, *key = NULL;
 	unsigned int buf_size;
 	int err;
 
-	err = __crypto_dh_decode_key(buffer, len, &params);
-	if (err)
-		return err;
-
-	if (params.p_size || params.g_size)
-		return -EINVAL;
+	if (buffer) {
+		err = __crypto_dh_decode_key(buffer, len, &params);
+		if (err)
+			return err;
+		if (params.p_size || params.g_size)
+			return -EINVAL;
+	}
 
 	params.p = inst_ctx->safe_prime->p;
 	params.p_size = inst_ctx->safe_prime->p_size;
-- 
2.26.2