Tadeusz Struk [off-list ref] wrote:

+	pkey = keyring->payload.data[asym_crypto];
+	if (!pkey) {
+		key_put(keyring);
+		goto out;
+	}
+
+	err = setkey(private, pkey->key, pkey->keylen);
+	key_put(keyring);

Note that you may not assume that there's data there that you can use in this
manner.  The key might be a pointer to some hardware device such as a TPM.  I
have a TPM asymmetric subtype in progress.

I think this really needs to be driven from a keyctl() because you need to let
the asymmetric subtype decide how it wants to handle this.  I would suggest
adding KEYCTL_{ASYM_GETINFO,SIGN,VERIFY,ENCRYPT,DECRYPT} - the problem is how
to pass sufficient arguments, how to decrypt the private key and what metadata
needs to be passed vs what is inline with the data.

David