Fix d2i_PublicKey() for EC keys

o2i_ECPublicKey() requires an EC_KEY structure filled with an EC_GROUP.

o2i_ECPublicKey() is called by d2i_PublicKey(). In order to fulfill the
o2i_ECPublicKey()'s requirement, d2i_PublicKey() needs to be called with
an EVP_PKEY with an EC_KEY containing an EC_GROUP.

However, the call to EVP_PKEY_set_type() frees any existing key structure
inside the EVP_PKEY, thus freeing the EC_KEY with the EC_GROUP that
o2i_ECPublicKey() needs.

This means you can't d2i_PublicKey() for an EC key...

The fix is to check to see if the type is already set appropriately, and
if so, not call EVP_PKEY_set_type().

Reviewed-by: Paul Yang <yang.yang@baishancloud.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/8168)

crypto/asn1/d2i_pu.c

@@ -32,7 +32,7 @@ EVP_PKEY *d2i_PublicKey(int type, EVP_PKEY **a, const unsigned char **pp,
     } else
         ret = *a;
 
-    if (!EVP_PKEY_set_type(ret, type)) {
+    if (type != EVP_PKEY_id(ret) && !EVP_PKEY_set_type(ret, type)) {
         ASN1err(ASN1_F_D2I_PUBLICKEY, ERR_R_EVP_LIB);
         goto err;
     }