Remove a TODO(3.0) from EVP_PKEY_derive_set_peer()

The TODO described a case where a legacy derive operation is called, but
the peer key is provider based. In practice this will almost never be a
problem. We should never end up in our own legacy EVP_PKEY_METHOD
implementations if no ENGINE has been configured. If an ENGINE has been
configured then we we will be using a third party EVP_PKEY_METHOD
implementation and public APIs will be used to obtain the key data from the
peer key so there will be no "reaching inside" the pkey.

There is a theoretical case where a third party ENGINE wraps our own
internal EVP_PKEY_METHODs using EVP_PKEY_meth_find() or
EVP_PKEY_meth_get0(). For these cases we just ensure all our
EVP_PKEY_METHODs never reach "inside" the implementation of a peer key. We
can never assume that it is a legacy key.

Fixes #14399

Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14555)

2 files changed, 10 insertions, 3 deletions

diff --git a/crypto/ec/ec_pmeth.c b/crypto/ec/ec_pmeth.c
index 2280189e28..e4f3549d30 100644
--- a/crypto/ec/ec_pmeth.c
+++ b/crypto/ec/ec_pmeth.c
@@ -161,8 +161,15 @@ static int pkey_ec_derive(EVP_PKEY_CTX *ctx, unsigned char *key, size_t *keylen)
     size_t outlen;
     const EC_POINT *pubkey = NULL;
     EC_KEY *eckey;
+    const EC_KEY *eckeypub;
     EC_PKEY_CTX *dctx = ctx->data;
-    if (!ctx->pkey || !ctx->peerkey) {
+
+    if (ctx->pkey == NULL || ctx->peerkey == NULL) {
+        ERR_raise(ERR_LIB_EC, EC_R_KEYS_NOT_SET);
+        return 0;
+    }
+    eckeypub = EVP_PKEY_get0_EC_KEY(ctx->peerkey);
+    if (eckeypub == NULL) {
         ERR_raise(ERR_LIB_EC, EC_R_KEYS_NOT_SET);
         return 0;
     }
@@ -178,7 +185,7 @@ static int pkey_ec_derive(EVP_PKEY_CTX *ctx, unsigned char *key, size_t *keylen)
         *keylen = (EC_GROUP_get_degree(group) + 7) / 8;
         return 1;
     }
-    pubkey = EC_KEY_get0_public_key(ctx->peerkey->pkey.ec);
+    pubkey = EC_KEY_get0_public_key(eckeypub);
 
     /*
      * NB: unlike PKCS#3 DH, if *outlen is less than maximum size this is not
diff --git a/crypto/ec/ecx_meth.c b/crypto/ec/ecx_meth.c
index cd73a15847..9a812c875b 100644
--- a/crypto/ec/ecx_meth.c
+++ b/crypto/ec/ecx_meth.c
@@ -766,7 +766,7 @@ static int validate_ecx_derive(EVP_PKEY_CTX *ctx, unsigned char *key,
         return 0;
     }
     ecxkey = ctx->pkey->pkey.ecx;
-    peerkey = ctx->peerkey->pkey.ecx;
+    peerkey = EVP_PKEY_get0(ctx->peerkey);
     if (ecxkey == NULL || ecxkey->privkey == NULL) {
         ERR_raise(ERR_LIB_EC, EC_R_INVALID_PRIVATE_KEY);
         return 0;