net: mctp: separate routing database from routing operations

This change adds a struct mctp_dst, representing the result of a routing
lookup. This decouples the struct mctp_route from the actual
implementation of a routing operation.

This will allow for future routing changes which may require more
involved lookup logic, such as gateway routing - which may require
multiple traversals of the routing table.

Since we only use the struct mctp_route at lookup time, we no longer
hold routes over a routing operation, as we only need it to populate the
dst. However, we do hold the dev while the dst is active.

This requires some changes to the route test infrastructure, as we no
longer have a mock route to handle the route output operation, and
transient dsts are created by the routing code, so we can't override
them as easily.

Instead, we use kunit->priv to stash a packet queue, and a custom
dst_output function queues into that packet queue, which we can use for
later expectations.

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Link: https://patch.msgid.link/20250702-dev-forwarding-v5-3-1468191da8a4@codeconstruct.com.au
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

1 files changed, 110 insertions, 100 deletions

diff --git a/net/mctp/route.c b/net/mctp/route.c
index 128ac46dda5e..3985388a6035 100644
--- a/net/mctp/route.c
+++ b/net/mctp/route.c
@@ -32,7 +32,7 @@ static const unsigned long mctp_key_lifetime = 6 * CONFIG_HZ;
 static void mctp_flow_prepare_output(struct sk_buff *skb, struct mctp_dev *dev);
 
 /* route output callbacks */
-static int mctp_route_discard(struct mctp_route *route, struct sk_buff *skb)
+static int mctp_dst_discard(struct mctp_dst *dst, struct sk_buff *skb)
 {
 	kfree_skb(skb);
 	return 0;
@@ -368,7 +368,7 @@ static int mctp_frag_queue(struct mctp_sk_key *key, struct sk_buff *skb)
 	return 0;
 }
 
-static int mctp_route_input(struct mctp_route *route, struct sk_buff *skb)
+static int mctp_dst_input(struct mctp_dst *dst, struct sk_buff *skb)
 {
 	struct mctp_sk_key *key, *any_key = NULL;
 	struct net *net = dev_net(skb->dev);
@@ -559,24 +559,17 @@ out:
 	return rc;
 }
 
-static unsigned int mctp_route_mtu(struct mctp_route *rt)
-{
-	return rt->mtu ?: READ_ONCE(rt->dev->dev->mtu);
-}
-
-static int mctp_route_output(struct mctp_route *route, struct sk_buff *skb)
+static int mctp_dst_output(struct mctp_dst *dst, struct sk_buff *skb)
 {
 	struct mctp_skb_cb *cb = mctp_cb(skb);
 	struct mctp_hdr *hdr = mctp_hdr(skb);
 	char daddr_buf[MAX_ADDR_LEN];
 	char *daddr = NULL;
-	unsigned int mtu;
 	int rc;
 
 	skb->protocol = htons(ETH_P_MCTP);
 
-	mtu = READ_ONCE(skb->dev->mtu);
-	if (skb->len > mtu) {
+	if (skb->len > dst->mtu) {
 		kfree_skb(skb);
 		return -EMSGSIZE;
 	}
@@ -598,7 +591,7 @@ static int mctp_route_output(struct mctp_route *route, struct sk_buff *skb)
 	} else {
 		skb->pkt_type = PACKET_OUTGOING;
 		/* If lookup fails let the device handle daddr==NULL */
-		if (mctp_neigh_lookup(route->dev, hdr->dest, daddr_buf) == 0)
+		if (mctp_neigh_lookup(dst->dev, hdr->dest, daddr_buf) == 0)
 			daddr = daddr_buf;
 	}
 
@@ -609,7 +602,7 @@ static int mctp_route_output(struct mctp_route *route, struct sk_buff *skb)
 		return -EHOSTUNREACH;
 	}
 
-	mctp_flow_prepare_output(skb, route->dev);
+	mctp_flow_prepare_output(skb, dst->dev);
 
 	rc = dev_queue_xmit(skb);
 	if (rc)
@@ -638,7 +631,7 @@ static struct mctp_route *mctp_route_alloc(void)
 
 	INIT_LIST_HEAD(&rt->list);
 	refcount_set(&rt->refs, 1);
-	rt->output = mctp_route_discard;
+	rt->output = mctp_dst_discard;
 
 	return rt;
 }
@@ -828,49 +821,106 @@ static bool mctp_rt_compare_exact(struct mctp_route *rt1,
 		rt1->max == rt2->max;
 }
 
-struct mctp_route *mctp_route_lookup(struct net *net, unsigned int dnet,
-				     mctp_eid_t daddr)
+static void mctp_dst_from_route(struct mctp_dst *dst, struct mctp_route *route)
+{
+	mctp_dev_hold(route->dev);
+	dst->dev = route->dev;
+	dst->mtu = route->mtu ?: READ_ONCE(dst->dev->dev->mtu);
+	dst->halen = 0;
+	dst->output = route->output;
+}
+
+int mctp_dst_from_extaddr(struct mctp_dst *dst, struct net *net, int ifindex,
+			  unsigned char halen, const unsigned char *haddr)
 {
-	struct mctp_route *tmp, *rt = NULL;
+	struct net_device *netdev;
+	struct mctp_dev *dev;
+	int rc = -ENOENT;
+
+	if (halen > sizeof(dst->haddr))
+		return -EINVAL;
 
 	rcu_read_lock();
 
-	list_for_each_entry_rcu(tmp, &net->mctp.routes, list) {
+	netdev = dev_get_by_index_rcu(net, ifindex);
+	if (!netdev)
+		goto out_unlock;
+
+	if (netdev->addr_len != halen) {
+		rc = -EINVAL;
+		goto out_unlock;
+	}
+
+	dev = __mctp_dev_get(netdev);
+	if (!dev)
+		goto out_unlock;
+
+	dst->dev = dev;
+	dst->mtu = READ_ONCE(netdev->mtu);
+	dst->halen = halen;
+	dst->output = mctp_dst_output;
+	memcpy(dst->haddr, haddr, halen);
+
+	rc = 0;
+
+out_unlock:
+	rcu_read_unlock();
+	return rc;
+}
+
+void mctp_dst_release(struct mctp_dst *dst)
+{
+	mctp_dev_put(dst->dev);
+}
+
+/* populates *dst on successful lookup, if set */
+int mctp_route_lookup(struct net *net, unsigned int dnet,
+		      mctp_eid_t daddr, struct mctp_dst *dst)
+{
+	int rc = -EHOSTUNREACH;
+	struct mctp_route *rt;
+
+	rcu_read_lock();
+
+	list_for_each_entry_rcu(rt, &net->mctp.routes, list) {
 		/* TODO: add metrics */
-		if (mctp_rt_match_eid(tmp, dnet, daddr)) {
-			if (refcount_inc_not_zero(&tmp->refs)) {
-				rt = tmp;
-				break;
-			}
-		}
+		if (!mctp_rt_match_eid(rt, dnet, daddr))
+			continue;
+
+		if (dst)
+			mctp_dst_from_route(dst, rt);
+		rc = 0;
+		break;
 	}
 
 	rcu_read_unlock();
 
-	return rt;
+	return rc;
 }
 
-static struct mctp_route *mctp_route_lookup_null(struct net *net,
-						 struct net_device *dev)
+static int mctp_route_lookup_null(struct net *net, struct net_device *dev,
+				  struct mctp_dst *dst)
 {
-	struct mctp_route *tmp, *rt = NULL;
+	int rc = -EHOSTUNREACH;
+	struct mctp_route *rt;
 
 	rcu_read_lock();
 
-	list_for_each_entry_rcu(tmp, &net->mctp.routes, list) {
-		if (tmp->dev->dev == dev && tmp->type == RTN_LOCAL &&
-		    refcount_inc_not_zero(&tmp->refs)) {
-			rt = tmp;
-			break;
-		}
+	list_for_each_entry_rcu(rt, &net->mctp.routes, list) {
+		if (rt->dev->dev != dev || rt->type != RTN_LOCAL)
+			continue;
+
+		mctp_dst_from_route(dst, rt);
+		rc = 0;
+		break;
 	}
 
 	rcu_read_unlock();
 
-	return rt;
+	return rc;
 }
 
-static int mctp_do_fragment_route(struct mctp_route *rt, struct sk_buff *skb,
+static int mctp_do_fragment_route(struct mctp_dst *dst, struct sk_buff *skb,
 				  unsigned int mtu, u8 tag)
 {
 	const unsigned int hlen = sizeof(struct mctp_hdr);
@@ -943,7 +993,7 @@ static int mctp_do_fragment_route(struct mctp_route *rt, struct sk_buff *skb,
 		skb_ext_copy(skb2, skb);
 
 		/* do route */
-		rc = rt->output(rt, skb2);
+		rc = dst->output(dst, skb2);
 		if (rc)
 			break;
 
@@ -955,68 +1005,32 @@ static int mctp_do_fragment_route(struct mctp_route *rt, struct sk_buff *skb,
 	return rc;
 }
 
-int mctp_local_output(struct sock *sk, struct mctp_route *rt,
+int mctp_local_output(struct sock *sk, struct mctp_dst *dst,
 		      struct sk_buff *skb, mctp_eid_t daddr, u8 req_tag)
 {
 	struct mctp_sock *msk = container_of(sk, struct mctp_sock, sk);
 	struct mctp_skb_cb *cb = mctp_cb(skb);
-	struct mctp_route tmp_rt = {0};
 	struct mctp_sk_key *key;
 	struct mctp_hdr *hdr;
 	unsigned long flags;
 	unsigned int netid;
 	unsigned int mtu;
 	mctp_eid_t saddr;
-	bool ext_rt;
 	int rc;
 	u8 tag;
 
 	rc = -ENODEV;
 
-	if (rt) {
-		ext_rt = false;
-		if (WARN_ON(!rt->dev))
-			goto out_release;
-
-	} else if (cb->ifindex) {
-		struct net_device *dev;
-
-		ext_rt = true;
-		rt = &tmp_rt;
-
-		rcu_read_lock();
-		dev = dev_get_by_index_rcu(sock_net(sk), cb->ifindex);
-		if (!dev) {
-			rcu_read_unlock();
-			goto out_free;
-		}
-		rt->dev = __mctp_dev_get(dev);
-		rcu_read_unlock();
-
-		if (!rt->dev)
-			goto out_release;
-
-		/* establish temporary route - we set up enough to keep
-		 * mctp_route_output happy
-		 */
-		rt->output = mctp_route_output;
-		rt->mtu = 0;
-
-	} else {
-		rc = -EINVAL;
-		goto out_free;
-	}
-
-	spin_lock_irqsave(&rt->dev->addrs_lock, flags);
-	if (rt->dev->num_addrs == 0) {
+	spin_lock_irqsave(&dst->dev->addrs_lock, flags);
+	if (dst->dev->num_addrs == 0) {
 		rc = -EHOSTUNREACH;
 	} else {
 		/* use the outbound interface's first address as our source */
-		saddr = rt->dev->addrs[0];
+		saddr = dst->dev->addrs[0];
 		rc = 0;
 	}
-	spin_unlock_irqrestore(&rt->dev->addrs_lock, flags);
-	netid = READ_ONCE(rt->dev->net);
+	spin_unlock_irqrestore(&dst->dev->addrs_lock, flags);
+	netid = READ_ONCE(dst->dev->net);
 
 	if (rc)
 		goto out_release;
@@ -1048,7 +1062,7 @@ int mctp_local_output(struct sock *sk, struct mctp_route *rt,
 	skb_reset_transport_header(skb);
 	skb_push(skb, sizeof(struct mctp_hdr));
 	skb_reset_network_header(skb);
-	skb->dev = rt->dev->dev;
+	skb->dev = dst->dev->dev;
 
 	/* cb->net will have been set on initial ingress */
 	cb->src = saddr;
@@ -1059,26 +1073,20 @@ int mctp_local_output(struct sock *sk, struct mctp_route *rt,
 	hdr->dest = daddr;
 	hdr->src = saddr;
 
-	mtu = mctp_route_mtu(rt);
+	mtu = dst->mtu;
 
 	if (skb->len + sizeof(struct mctp_hdr) <= mtu) {
 		hdr->flags_seq_tag = MCTP_HDR_FLAG_SOM |
 			MCTP_HDR_FLAG_EOM | tag;
-		rc = rt->output(rt, skb);
+		rc = dst->output(dst, skb);
 	} else {
-		rc = mctp_do_fragment_route(rt, skb, mtu, tag);
+		rc = mctp_do_fragment_route(dst, skb, mtu, tag);
 	}
 
 	/* route output functions consume the skb, even on error */
 	skb = NULL;
 
 out_release:
-	if (!ext_rt)
-		mctp_route_release(rt);
-
-	mctp_dev_put(tmp_rt.dev);
-
-out_free:
 	kfree_skb(skb);
 	return rc;
 }
@@ -1088,7 +1096,7 @@ static int mctp_route_add(struct mctp_dev *mdev, mctp_eid_t daddr_start,
 			  unsigned int daddr_extent, unsigned int mtu,
 			  unsigned char type)
 {
-	int (*rtfn)(struct mctp_route *rt, struct sk_buff *skb);
+	int (*rtfn)(struct mctp_dst *dst, struct sk_buff *skb);
 	struct net *net = dev_net(mdev->dev);
 	struct mctp_route *rt, *ert;
 
@@ -1100,15 +1108,17 @@ static int mctp_route_add(struct mctp_dev *mdev, mctp_eid_t daddr_start,
 
 	switch (type) {
 	case RTN_LOCAL:
-		rtfn = mctp_route_input;
+		rtfn = mctp_dst_input;
 		break;
 	case RTN_UNICAST:
-		rtfn = mctp_route_output;
+		rtfn = mctp_dst_output;
 		break;
 	default:
 		return -EINVAL;
 	}
 
+	ASSERT_RTNL();
+
 	rt = mctp_route_alloc();
 	if (!rt)
 		return -ENOMEM;
@@ -1121,7 +1131,6 @@ static int mctp_route_add(struct mctp_dev *mdev, mctp_eid_t daddr_start,
 	rt->type = type;
 	rt->output = rtfn;
 
-	ASSERT_RTNL();
 	/* Prevent duplicate identical routes. */
 	list_for_each_entry(ert, &net->mctp.routes, list) {
 		if (mctp_rt_compare_exact(rt, ert)) {
@@ -1200,8 +1209,9 @@ static int mctp_pkttype_receive(struct sk_buff *skb, struct net_device *dev,
 	struct net *net = dev_net(dev);
 	struct mctp_dev *mdev;
 	struct mctp_skb_cb *cb;
-	struct mctp_route *rt;
+	struct mctp_dst dst;
 	struct mctp_hdr *mh;
+	int rc;
 
 	rcu_read_lock();
 	mdev = __mctp_dev_get(dev);
@@ -1243,17 +1253,17 @@ static int mctp_pkttype_receive(struct sk_buff *skb, struct net_device *dev,
 	cb->net = READ_ONCE(mdev->net);
 	cb->ifindex = dev->ifindex;
 
-	rt = mctp_route_lookup(net, cb->net, mh->dest);
+	rc = mctp_route_lookup(net, cb->net, mh->dest, &dst);
 
 	/* NULL EID, but addressed to our physical address */
-	if (!rt && mh->dest == MCTP_ADDR_NULL && skb->pkt_type == PACKET_HOST)
-		rt = mctp_route_lookup_null(net, dev);
+	if (rc && mh->dest == MCTP_ADDR_NULL && skb->pkt_type == PACKET_HOST)
+		rc = mctp_route_lookup_null(net, dev, &dst);
 
-	if (!rt)
+	if (rc)
 		goto err_drop;
 
-	rt->output(rt, skb);
-	mctp_route_release(rt);
+	dst.output(&dst, skb);
+	mctp_dst_release(&dst);
 	mctp_dev_put(mdev);
 
 	return NET_RX_SUCCESS;