[PATCH v2 10/18] crypto: dh - introduce support for ephemeral key generation to dh-generic

[Nicolai Stange <nstange@xxxxxxx>]

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@xxxxxxx

Signed-off-by: Nicolai Stange <nstange@xxxxxxx>
Reviewed-by: Hannes Reinecke <hare@xxxxxxx>
---
 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) {
+		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;
 }
 
 /*
-- 
2.26.2