crypto: dh - SP800-56A rev 3 local public key validation

After the generation of a local public key, SP800-56A rev 3 section
5.6.2.1.3 mandates a validation of that key with a full validation
compliant to section 5.6.2.3.1.

Only if the full validation passes, the key is allowed to be used.
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/dh.c

@@ -180,8 +180,9 @@ static int dh_compute_value(struct kpp_request *req)
 	if (ret)
 		goto err_free_base;
 
+	if (fips_enabled) {
 		/* SP800-56A rev3 5.7.1.1 check: Validation of shared secret */
-	if (fips_enabled && req->src) {
+		if (req->src) {
 			MPI pone;
 
 			/* z <= 1 */
@@ -206,6 +207,14 @@ static int dh_compute_value(struct kpp_request *req)
 
 			if (ret)
 				goto err_free_base;
+
+		/* SP800-56A rev 3 5.6.2.1.3 key check */
+		} else {
+			if (dh_is_pubkey_valid(ctx, val)) {
+				ret = -EAGAIN;
+				goto err_free_val;
+			}
+		}
 	}
 
 	ret = mpi_write_to_sgl(val, req->dst, req->dst_len, &sign);