EVP_PKEY_get0 implementation (aws#1749)

### Issues:
Addresses CryptoAlg-1716

### Description of changes: 
* Provide a working implementation of the (deprecated) function
`EVP_PKEY_get0`.

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license and the ISC license.

crypto/asn1/asn1_test.cc

@@ -2462,9 +2462,13 @@ TEST(ASN1Test, ASN1Dup) {
             0);
 
   bssl::UniquePtr<EVP_PKEY> evp_pkey(EVP_PKEY_new());
+  OPENSSL_BEGIN_ALLOW_DEPRECATED
+  ASSERT_FALSE(EVP_PKEY_get0(evp_pkey.get()));
   X509_PUBKEY *tmp_key = nullptr;
   ASSERT_TRUE(evp_pkey);
   ASSERT_TRUE(EVP_PKEY_set1_EC_KEY(evp_pkey.get(), key.get()));
+  ASSERT_EQ(key.get(), EVP_PKEY_get0(evp_pkey.get()));
+  OPENSSL_END_ALLOW_DEPRECATED
   ASSERT_TRUE(X509_PUBKEY_set(&tmp_key, evp_pkey.get()));
   bssl::UniquePtr<X509_PUBKEY> x509_pubkey(tmp_key);
   bssl::UniquePtr<X509_PUBKEY> x509_pubkey_copy((X509_PUBKEY *)ASN1_dup(

crypto/ecdh_extra/ecdh_test.cc

@@ -264,7 +264,9 @@ static void RunWycheproofTest(FileTest *t) {
   }
   EC_KEY *peer_ec = EVP_PKEY_get0_EC_KEY(peer_evp.get());
   ASSERT_TRUE(peer_ec);
-
+  OPENSSL_BEGIN_ALLOW_DEPRECATED
+  ASSERT_EQ(peer_ec, EVP_PKEY_get0(peer_evp.get()));
+  OPENSSL_END_ALLOW_DEPRECATED
   bssl::UniquePtr<EC_KEY> key(EC_KEY_new());
   ASSERT_TRUE(key);
   ASSERT_TRUE(EC_KEY_set_group(key.get(), group));

crypto/evp_extra/evp_test.cc

@@ -662,6 +662,9 @@ static void RunWycheproofVerifyTest(const char *path) {
     if (EVP_PKEY_id(key.get()) == EVP_PKEY_DSA) {
       // DSA is deprecated and is not usable via EVP.
       DSA *dsa = EVP_PKEY_get0_DSA(key.get());
+      OPENSSL_BEGIN_ALLOW_DEPRECATED
+      ASSERT_EQ(dsa, EVP_PKEY_get0(key.get()));
+      OPENSSL_END_ALLOW_DEPRECATED
       uint8_t digest[EVP_MAX_MD_SIZE];
       unsigned digest_len;
       ASSERT_TRUE(
@@ -1022,6 +1025,9 @@ static EVP_PKEY * instantiate_and_set_private_key(const uint8_t *private_key,
   size_t private_key_size, int key_type, int curve_nid) {
 
   EVP_PKEY *pkey = NULL;
+  OPENSSL_BEGIN_ALLOW_DEPRECATED
+  EXPECT_FALSE(EVP_PKEY_get0(pkey));
+  OPENSSL_END_ALLOW_DEPRECATED
 
   if (NID_X25519 == curve_nid) {
     pkey = EVP_PKEY_new_raw_private_key(curve_nid, nullptr, private_key,
@@ -1037,7 +1043,11 @@ static EVP_PKEY * instantiate_and_set_private_key(const uint8_t *private_key,
     BN_free(private_key_bn);
     pkey = EVP_PKEY_new();
     EXPECT_TRUE(pkey);
+    OPENSSL_BEGIN_ALLOW_DEPRECATED
+    EXPECT_FALSE(EVP_PKEY_get0(pkey));
     EXPECT_TRUE(EVP_PKEY_assign(pkey, key_type, (EC_KEY *) ec_key));
+    EXPECT_EQ(ec_key, EVP_PKEY_get0(pkey));
+    OPENSSL_END_ALLOW_DEPRECATED
   }
 
   return pkey;

crypto/fipsmodule/evp/evp.c

@@ -581,12 +581,16 @@ int EVP_PKEY_CTX_get_signature_md(EVP_PKEY_CTX *ctx, const EVP_MD **out_md) {
 
 void *EVP_PKEY_get0(const EVP_PKEY *pkey) {
   SET_DIT_AUTO_DISABLE;
-  // Node references, but never calls this function, so for now we return NULL.
-  // If other projects require complete support, call |EVP_PKEY_get0_RSA|, etc.,
-  // rather than reading |pkey->pkey.ptr| directly. This avoids problems if our
-  // internal representation does not match the type the caller expects from
-  // OpenSSL.
-  return NULL;
+  GUARD_PTR(pkey);
+  switch (pkey->type) {
+    case EVP_PKEY_RSA:
+    case EVP_PKEY_RSA_PSS:
+    case EVP_PKEY_DSA:
+    case EVP_PKEY_EC:
+      return pkey->pkey.ptr;
+    default:
+      return NULL;
+  }
 }
 
 void OpenSSL_add_all_algorithms(void) {}

include/openssl/evp.h

@@ -1142,17 +1142,18 @@ OPENSSL_EXPORT EVP_PKEY *EVP_PKEY_new_mac_key(int type, ENGINE *engine,
                                               size_t mac_key_len);
 
 
-// General No-op Functions [Deprecated].
+// Deprecated functions
 
-// EVP_PKEY_get0 returns NULL. This function is provided for compatibility with
-// OpenSSL but does not return anything. Use the typed |EVP_PKEY_get0_*|
-// functions instead.
+// EVP_PKEY_get0 returns the consumed key. The type of value returned will be
+// one of the following, depending on the type of the |EVP_PKEY|:
+// |RSA|, |DSA| or |EC_KEY|.
 //
-// Note: In OpenSSL, the returned type will be different depending on the type
-//       of |EVP_PKEY| consumed. This leads to misuage very easily and has been
-//       deprecated as a no-op to avoid so.
+// This function is provided only for compatibility with OpenSSL.
+// Prefer the use the typed |EVP_PKEY_get0_*| functions instead.
 OPENSSL_EXPORT OPENSSL_DEPRECATED void *EVP_PKEY_get0(const EVP_PKEY *pkey);
 
+// General No-op Functions [Deprecated].
+
 // OpenSSL_add_all_algorithms does nothing. This has been deprecated since
 // OpenSSL 1.1.0.
 //