[PATCH v3 11/15] crypto: dh - allow for passing NULL to the ffdheXYZ(dh)s' ->set_secret()

Nicolai Stange
2022-02-02T10:42:21Z

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