xfrm: Define new XFRM netlink auth attribute with specified truncation bits

The new XFRMA_ALG_AUTH_TRUNC attribute taking a xfrm_algo_auth as
argument allows the installation of authentication algorithms with
a truncation length specified in userspace, i.e. SHA256 with 128 bit
instead of 96 bit truncation.
Signed-off-by: Martin Willi <martin@strongswan.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/xfrm.h

@@ -90,6 +90,13 @@ struct xfrm_algo {
 	char		alg_key[0];
 };
 
+struct xfrm_algo_auth {
+	char		alg_name[64];
+	unsigned int	alg_key_len;    /* in bits */
+	unsigned int	alg_trunc_len;  /* in bits */
+	char		alg_key[0];
+};
+
 struct xfrm_algo_aead {
 	char		alg_name[64];
 	unsigned int	alg_key_len;	/* in bits */
@@ -274,6 +281,7 @@ enum xfrm_attr_type_t {
 	XFRMA_MIGRATE,
 	XFRMA_ALG_AEAD,		/* struct xfrm_algo_aead */
 	XFRMA_KMADDRESS,        /* struct xfrm_user_kmaddress */
+	XFRMA_ALG_AUTH_TRUNC,	/* struct xfrm_algo_auth */
 	__XFRMA_MAX
 
 #define XFRMA_MAX (__XFRMA_MAX - 1)