xfrm: Add a XFRM_STATE_AF_UNSPEC flag to xfrm_usersa_info

Add a XFRM_STATE_AF_UNSPEC flag to handle the AF_UNSPEC behavior for
the selector family. Userspace applications can set this flag to leave
the selector family of the xfrm_state unspecified.  This can be used
to to handle inter family tunnels if the selector is not set from
userspace.
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/xfrm.h

@@ -339,6 +339,7 @@ struct xfrm_usersa_info {
 #define XFRM_STATE_NOPMTUDISC	4
 #define XFRM_STATE_WILDRECV	8
 #define XFRM_STATE_ICMP		16
+#define XFRM_STATE_AF_UNSPEC	32
 };
 
 struct xfrm_usersa_id {

net/xfrm/xfrm_user.c

@@ -277,9 +277,8 @@ static void copy_from_user_state(struct xfrm_state *x, struct xfrm_usersa_info *
 	memcpy(&x->props.saddr, &p->saddr, sizeof(x->props.saddr));
 	x->props.flags = p->flags;
 
-	if (!x->sel.family)
+	if (!x->sel.family && !(p->flags & XFRM_STATE_AF_UNSPEC))
 		x->sel.family = p->family;
-
 }
 
 /*