crypto: af_alg - add setsockopt for auth tag size

Use setsockopt on the tfm FD to provide the authentication tag size for
an AEAD cipher. This is achieved by adding a callback function which is
intended to be used by the AEAD AF_ALG implementation.

The optlen argument of the setsockopt specifies the authentication tag
size to be used with the AEAD tfm.
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/af_alg.c

@@ -215,6 +215,13 @@ static int alg_setsockopt(struct socket *sock, int level, int optname,
 			goto unlock;
 
 		err = alg_setkey(sk, optval, optlen);
+		break;
+	case ALG_SET_AEAD_AUTHSIZE:
+		if (sock->state == SS_CONNECTED)
+			goto unlock;
+		if (!type->setauthsize)
+			goto unlock;
+		err = type->setauthsize(ask->private, optlen);
 	}
 
 unlock:

include/crypto/if_alg.h

@@ -50,6 +50,7 @@ struct af_alg_type {
 	void (*release)(void *private);
 	int (*setkey)(void *private, const u8 *key, unsigned int keylen);
 	int (*accept)(void *private, struct sock *sk);
+	int (*setauthsize)(void *private, unsigned int authsize);
 
 	struct proto_ops *ops;
 	struct module *owner;