net: mctp: allow NL parsing directly into a struct mctp_route

The netlink route parsing functions end up setting a bunch of output
variables from the rt attributes. This will get messy when the routes
become more complex.

So, split the rt parsing into two types: a lookup (returning route
target data suitable for a route lookup, like when deleting a route) and
a populate (setting fields of a struct mctp_route).

In doing this, we need to separate the route allocation from
mctp_route_add, so add some comments on the lifetime semantics for the
latter.

Signed-off-by: Jeremy Kerr <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Paolo Abeni <[e-mail]>

net/mctp/route.c

···
 }
 
 /* route management */
-static int mctp_route_add(struct net *net, struct mctp_dev *mdev,
-			  mctp_eid_t daddr_start, unsigned int daddr_extent,
-			  unsigned int mtu, unsigned char type)
+
+/* mctp_route_add(): Add the provided route, previously allocated via
+ * mctp_route_alloc(). On success, takes ownership of @rt, which includes a
+ * hold on rt->dev for usage in the route table. On failure a caller will want
+ * to mctp_route_release().
+ *
+ * We expect that the caller has set rt->type, rt->min, rt->max, rt->dev and
+ * rt->mtu, and that the route holds a reference to rt->dev (via mctp_dev_hold).
+ * Other fields will be populated.
+ */
+static int mctp_route_add(struct net *net, struct mctp_route *rt)
 {
-	int (*rtfn)(struct mctp_dst *dst, struct sk_buff *skb);
-	struct mctp_route *rt, *ert;
+	struct mctp_route *ert;
 
-	if (!mctp_address_unicast(daddr_start))
+	if (!mctp_address_unicast(rt->min) || !mctp_address_unicast(rt->max))
 		return -EINVAL;
 
-	if (daddr_extent > 0xff || daddr_start + daddr_extent >= 255)
+	if (!rt->dev)
 		return -EINVAL;
 
-	switch (type) {
+	switch (rt->type) {
 	case RTN_LOCAL:
-		rtfn = mctp_dst_input;
+		rt->output = mctp_dst_input;
 		break;
 	case RTN_UNICAST:
-		rtfn = mctp_dst_output;
+		rt->output = mctp_dst_output;
 		break;
 	default:
 		return -EINVAL;
···
 
 	ASSERT_RTNL();
 
-	rt = mctp_route_alloc();
-	if (!rt)
-		return -ENOMEM;
-
-	rt->min = daddr_start;
-	rt->max = daddr_start + daddr_extent;
-	rt->mtu = mtu;
-	rt->dev = mdev;
-	mctp_dev_hold(rt->dev);
-	rt->type = type;
-	rt->output = rtfn;
-
 	/* Prevent duplicate identical routes. */
 	list_for_each_entry(ert, &net->mctp.routes, list) {
 		if (mctp_rt_compare_exact(rt, ert)) {
-			mctp_route_release(rt);
 			return -EEXIST;
 		}
 	}
···
 
 int mctp_route_add_local(struct mctp_dev *mdev, mctp_eid_t addr)
 {
-	return mctp_route_add(dev_net(mdev->dev), mdev, addr, 0, 0, RTN_LOCAL);
+	struct mctp_route *rt;
+	int rc;
+
+	rt = mctp_route_alloc();
+	if (!rt)
+		return -ENOMEM;
+
+	rt->min = addr;
+	rt->max = addr;
+	rt->dev = mdev;
+	rt->type = RTN_LOCAL;
+
+	mctp_dev_hold(rt->dev);
+
+	rc = mctp_route_add(dev_net(mdev->dev), rt);
+	if (rc)
+		mctp_route_release(rt);
+
+	return rc;
 }
 
 int mctp_route_remove_local(struct mctp_dev *mdev, mctp_eid_t addr)
···
 	[RTA_OIF]		= { .type = NLA_U32 },
 };
 
-/* Common part for RTM_NEWROUTE and RTM_DELROUTE parsing.
- * tb must hold RTA_MAX+1 elements.
- */
-static int mctp_route_nlparse(struct net *net, struct nlmsghdr *nlh,
-			      struct netlink_ext_ack *extack,
-			      struct nlattr **tb, struct rtmsg **rtm,
-			      struct mctp_dev **mdev, mctp_eid_t *daddr_start)
+static const struct nla_policy rta_metrics_policy[RTAX_MAX + 1] = {
+	[RTAX_MTU]		= { .type = NLA_U32 },
+};
+
+/* base parsing; common to both _lookup and _populate variants */
+static int mctp_route_nlparse_common(struct net *net, struct nlmsghdr *nlh,
+				     struct netlink_ext_ack *extack,
+				     struct nlattr **tb, struct rtmsg **rtm,
+				     struct mctp_dev **mdev,
+				     mctp_eid_t *daddr_start)
 {
 	struct net_device *dev;
 	unsigned int ifindex;
···
 		return -EINVAL;
 	}
 
+	if ((*rtm)->rtm_type != RTN_UNICAST) {
+		NL_SET_ERR_MSG(extack, "rtm_type must be RTN_UNICAST");
+		return -EINVAL;
+	}
+
 	dev = __dev_get_by_index(net, ifindex);
 	if (!dev) {
 		NL_SET_ERR_MSG(extack, "bad ifindex");
 		return -ENODEV;
 	}
+
 	*mdev = mctp_dev_get_rtnl(dev);
 	if (!*mdev)
 		return -ENODEV;
 
-	if (dev->flags & IFF_LOOPBACK) {
-		NL_SET_ERR_MSG(extack, "no routes to loopback");
-		return -EINVAL;
-	}
+	return 0;
+}
+
+/* Route parsing for lookup operations; we only need the "route target"
+ * components (ie., network and dest-EID range).
+ */
+static int mctp_route_nlparse_lookup(struct net *net, struct nlmsghdr *nlh,
+				     struct netlink_ext_ack *extack,
+				     unsigned char *type, unsigned int *netid,
+				     mctp_eid_t *daddr_start,
+				     unsigned int *daddr_extent)
+{
+	struct nlattr *tb[RTA_MAX + 1];
+	struct mctp_dev *mdev;
+	struct rtmsg *rtm;
+	int rc;
+
+	rc = mctp_route_nlparse_common(net, nlh, extack, tb, &rtm,
+				       &mdev, daddr_start);
+	if (rc)
+		return rc;
+
+	*netid = mdev->net;
+	*type = rtm->rtm_type;
+	*daddr_extent = rtm->rtm_dst_len;
 
 	return 0;
 }
 
-static const struct nla_policy rta_metrics_policy[RTAX_MAX + 1] = {
-	[RTAX_MTU]		= { .type = NLA_U32 },
-};
+/* Full route parse for RTM_NEWROUTE: populate @rt. On success, the route will
+ * hold a reference to the dev.
+ */
+static int mctp_route_nlparse_populate(struct net *net, struct nlmsghdr *nlh,
+				       struct netlink_ext_ack *extack,
+				       struct mctp_route *rt)
+{
+	struct nlattr *tbx[RTAX_MAX + 1];
+	struct nlattr *tb[RTA_MAX + 1];
+	unsigned int daddr_extent;
+	mctp_eid_t daddr_start;
+	struct mctp_dev *dev;
+	struct rtmsg *rtm;
+	u32 mtu = 0;
+	int rc;
+
+	rc = mctp_route_nlparse_common(net, nlh, extack, tb, &rtm,
+				       &dev, &daddr_start);
+	if (rc)
+		return rc;
+
+	daddr_extent = rtm->rtm_dst_len;
+
+	if (daddr_extent > 0xff || daddr_extent + daddr_start >= 255) {
+		NL_SET_ERR_MSG(extack, "invalid eid range");
+		return -EINVAL;
+	}
+
+	if (tb[RTA_METRICS]) {
+		rc = nla_parse_nested(tbx, RTAX_MAX, tb[RTA_METRICS],
+				      rta_metrics_policy, NULL);
+		if (rc < 0) {
+			NL_SET_ERR_MSG(extack, "incorrect RTA_METRICS format");
+			return rc;
+		}
+		if (tbx[RTAX_MTU])
+			mtu = nla_get_u32(tbx[RTAX_MTU]);
+	}
+
+	rt->type = rtm->rtm_type;
+	rt->min = daddr_start;
+	rt->max = daddr_start + daddr_extent;
+	rt->mtu = mtu;
+	rt->dev = dev;
+	mctp_dev_hold(rt->dev);
+
+	return 0;
+}
 
 static int mctp_newroute(struct sk_buff *skb, struct nlmsghdr *nlh,
 			 struct netlink_ext_ack *extack)
 {
 	struct net *net = sock_net(skb->sk);
-	struct nlattr *tb[RTA_MAX + 1];
-	struct nlattr *tbx[RTAX_MAX + 1];
-	mctp_eid_t daddr_start;
-	struct mctp_dev *mdev;
-	struct rtmsg *rtm;
-	unsigned int mtu;
+	struct mctp_route *rt;
 	int rc;
 
-	rc = mctp_route_nlparse(net, nlh, extack, tb,
-				&rtm, &mdev, &daddr_start);
+	rt = mctp_route_alloc();
+	if (!rt)
+		return -ENOMEM;
+
+	rc = mctp_route_nlparse_populate(net, nlh, extack, rt);
 	if (rc < 0)
-		return rc;
+		goto err_free;
 
-	if (rtm->rtm_type != RTN_UNICAST) {
-		NL_SET_ERR_MSG(extack, "rtm_type must be RTN_UNICAST");
-		return -EINVAL;
+	if (rt->dev->dev->flags & IFF_LOOPBACK) {
+		NL_SET_ERR_MSG(extack, "no routes to loopback");
+		rc = -EINVAL;
+		goto err_free;
 	}
 
-	mtu = 0;
-	if (tb[RTA_METRICS]) {
-		rc = nla_parse_nested(tbx, RTAX_MAX, tb[RTA_METRICS],
-				      rta_metrics_policy, NULL);
-		if (rc < 0)
-			return rc;
-		if (tbx[RTAX_MTU])
-			mtu = nla_get_u32(tbx[RTAX_MTU]);
-	}
+	rc = mctp_route_add(net, rt);
+	if (!rc)
+		return 0;
 
-	rc = mctp_route_add(net, mdev, daddr_start, rtm->rtm_dst_len, mtu,
-			    rtm->rtm_type);
+err_free:
+	mctp_route_release(rt);
 	return rc;
 }
 
···
 			 struct netlink_ext_ack *extack)
 {
 	struct net *net = sock_net(skb->sk);
-	struct nlattr *tb[RTA_MAX + 1];
+	unsigned int netid, daddr_extent;
+	unsigned char type = RTN_UNSPEC;
 	mctp_eid_t daddr_start;
-	struct mctp_dev *mdev;
-	struct rtmsg *rtm;
 	int rc;
 
-	rc = mctp_route_nlparse(net, nlh, extack, tb,
-				&rtm, &mdev, &daddr_start);
+	rc = mctp_route_nlparse_lookup(net, nlh, extack, &type, &netid,
+				       &daddr_start, &daddr_extent);
 	if (rc < 0)
 		return rc;
 
 	/* we only have unicast routes */
-	if (rtm->rtm_type != RTN_UNICAST)
+	if (type != RTN_UNICAST)
 		return -EINVAL;
 
-	rc = mctp_route_remove(net, mdev->net, daddr_start, rtm->rtm_dst_len,
-			       RTN_UNICAST);
+	rc = mctp_route_remove(net, netid, daddr_start, daddr_extent, type);
 	return rc;
 }