xfrm: split xfrm_state_migrate into create and install functions

To prepare for subsequent patches, split
xfrm_state_migrate() into two functions:
- xfrm_state_migrate_create(): creates the migrated state
- xfrm_state_migrate_install(): installs it into the state table

splitting will help to avoid SN/IV reuse when migrating AEAD SA.

And add const whenever possible.
No functional change.

Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: Antony Antony <antony.antony@secunet.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

include/net/xfrm.h

@@ -1895,6 +1895,17 @@ int km_migrate(const struct xfrm_selector *sel, u8 dir, u8 type,
 	       const struct xfrm_encap_tmpl *encap);
 struct xfrm_state *xfrm_migrate_state_find(struct xfrm_migrate *m, struct net *net,
 						u32 if_id);
+struct xfrm_state *xfrm_state_migrate_create(struct xfrm_state *x,
+					     const struct xfrm_migrate *m,
+					     const struct xfrm_encap_tmpl *encap,
+					     struct net *net,
+					     struct xfrm_user_offload *xuo,
+					     struct netlink_ext_ack *extack);
+int xfrm_state_migrate_install(const struct xfrm_state *x,
+			       struct xfrm_state *xc,
+			       const struct xfrm_migrate *m,
+			       struct xfrm_user_offload *xuo,
+			       struct netlink_ext_ack *extack);
 struct xfrm_state *xfrm_state_migrate(struct xfrm_state *x,
 				      struct xfrm_migrate *m,
 				      struct xfrm_encap_tmpl *encap,

net/xfrm/xfrm_state.c

@@ -1966,8 +1966,8 @@ static inline int clone_security(struct xfrm_state *x, struct xfrm_sec_ctx *secu
 }
 
 static struct xfrm_state *xfrm_state_clone_and_setup(struct xfrm_state *orig,
-					   struct xfrm_encap_tmpl *encap,
+					   const struct xfrm_encap_tmpl *encap,
-					   struct xfrm_migrate *m)
+					   const struct xfrm_migrate *m)
 {
 	struct net *net = xs_net(orig);
 	struct xfrm_state *x = xfrm_state_alloc(net);
@@ -2125,12 +2125,12 @@ struct xfrm_state *xfrm_migrate_state_find(struct xfrm_migrate *m, struct net *n
 }
 EXPORT_SYMBOL(xfrm_migrate_state_find);
 
-struct xfrm_state *xfrm_state_migrate(struct xfrm_state *x,
+struct xfrm_state *xfrm_state_migrate_create(struct xfrm_state *x,
-				      struct xfrm_migrate *m,
+					     const struct xfrm_migrate *m,
-				      struct xfrm_encap_tmpl *encap,
+					     const struct xfrm_encap_tmpl *encap,
-				      struct net *net,
+					     struct net *net,
-				      struct xfrm_user_offload *xuo,
+					     struct xfrm_user_offload *xuo,
-				      struct netlink_ext_ack *extack)
+					     struct netlink_ext_ack *extack)
 {
 	struct xfrm_state *xc;
 
@@ -2145,25 +2145,58 @@ struct xfrm_state *xfrm_state_migrate(struct xfrm_state *x,
 	if (xuo && xfrm_dev_state_add(net, xc, xuo, extack))
 		goto error;
 
-	/* add state */
-	if (xfrm_addr_equal(&x->id.daddr, &m->new_daddr, m->new_family)) {
-		/* a care is needed when the destination address of the
-		   state is to be updated as it is a part of triplet */
-		xfrm_state_insert(xc);
-	} else {
-		if (xfrm_state_add(xc) < 0)
-			goto error_add;
-	}
-
 	return xc;
-error_add:
-	if (xuo)
-		xfrm_dev_state_delete(xc);
 error:
 	xc->km.state = XFRM_STATE_DEAD;
 	xfrm_state_put(xc);
 	return NULL;
 }
+EXPORT_SYMBOL(xfrm_state_migrate_create);
+
+int xfrm_state_migrate_install(const struct xfrm_state *x,
+			       struct xfrm_state *xc,
+			       const struct xfrm_migrate *m,
+			       struct xfrm_user_offload *xuo,
+			       struct netlink_ext_ack *extack)
+{
+	if (xfrm_addr_equal(&x->id.daddr, &m->new_daddr, m->new_family)) {
+		/*
+		 * Care is needed when the destination address
+		 * of the state is to be updated as it is a part of triplet.
+		 */
+		xfrm_state_insert(xc);
+	} else {
+		if (xfrm_state_add(xc) < 0) {
+			if (xuo)
+				xfrm_dev_state_delete(xc);
+			xc->km.state = XFRM_STATE_DEAD;
+			xfrm_state_put(xc);
+			return -EEXIST;
+		}
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(xfrm_state_migrate_install);
+
+struct xfrm_state *xfrm_state_migrate(struct xfrm_state *x,
+				      struct xfrm_migrate *m,
+				      struct xfrm_encap_tmpl *encap,
+				      struct net *net,
+				      struct xfrm_user_offload *xuo,
+				      struct netlink_ext_ack *extack)
+{
+	struct xfrm_state *xc;
+
+	xc = xfrm_state_migrate_create(x, m, encap, net, xuo, extack);
+	if (!xc)
+		return NULL;
+
+	if (xfrm_state_migrate_install(x, xc, m, xuo, extack) < 0)
+		return NULL;
+
+	return xc;
+}
 EXPORT_SYMBOL(xfrm_state_migrate);
 #endif