PROV: Fix DSA and DH private key serializers

If those private key serializer were given a key structure with just
the public key material, they crashed, because they tried to
de-reference NULL.  This adds better checking.

Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/12679)

1 files changed, 14 insertions, 4 deletions

diff --git a/providers/implementations/serializers/serializer_dh.c b/providers/implementations/serializers/serializer_dh.c
index d63c8402f9..d1b1d27cf6 100644
--- a/providers/implementations/serializers/serializer_dh.c
+++ b/providers/implementations/serializers/serializer_dh.c
@@ -119,10 +119,15 @@ int ossl_prov_prepare_dh_params(const void *dh, int nid,
 
 int ossl_prov_dh_pub_to_der(const void *dh, unsigned char **pder)
 {
-    ASN1_INTEGER *pub_key = BN_to_ASN1_INTEGER(DH_get0_pub_key(dh), NULL);
+    const BIGNUM *bn = NULL;
+    ASN1_INTEGER *pub_key = NULL;
     int ret;
 
-    if (pub_key == NULL) {
+    if ((bn = DH_get0_pub_key(dh)) == NULL) {
+        ERR_raise(ERR_LIB_PROV, PROV_R_NOT_A_PUBLIC_KEY);
+        return 0;
+    }
+    if ((pub_key = BN_to_ASN1_INTEGER(bn, NULL)) == NULL) {
         ERR_raise(ERR_LIB_PROV, PROV_R_BN_ERROR);
         return 0;
     }
@@ -135,10 +140,15 @@ int ossl_prov_dh_pub_to_der(const void *dh, unsigned char **pder)
 
 int ossl_prov_dh_priv_to_der(const void *dh, unsigned char **pder)
 {
-    ASN1_INTEGER *priv_key = BN_to_ASN1_INTEGER(DH_get0_priv_key(dh), NULL);
+    const BIGNUM *bn = NULL;
+    ASN1_INTEGER *priv_key = NULL;
     int ret;
 
-    if (priv_key == NULL) {
+    if ((bn = DH_get0_priv_key(dh)) == NULL) {
+        ERR_raise(ERR_LIB_PROV, PROV_R_NOT_A_PRIVATE_KEY);
+        return 0;
+    }
+    if ((priv_key = BN_to_ASN1_INTEGER(bn, NULL)) == NULL) {
         ERR_raise(ERR_LIB_PROV, PROV_R_BN_ERROR);
         return 0;
     }