net: mctp: Use hashtable for binds

Ensure that a specific EID (remote or local) bind will match in
preference to a MCTP_ADDR_ANY bind.

This adds infrastructure for binding a socket to receive messages from a
specific remote peer address, a future commit will expose an API for
this.

Signed-off-by: Matt Johnston <matt@codeconstruct.com.au>
Link: https://patch.msgid.link/20250710-mctp-bind-v4-5-8ec2f6460c56@codeconstruct.com.au
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

include/net/netns/mctp.h

@@ -6,19 +6,25 @@
 #ifndef __NETNS_MCTP_H__
 #define __NETNS_MCTP_H__
 
+#include <linux/hash.h>
+#include <linux/hashtable.h>
 #include <linux/mutex.h>
 #include <linux/types.h>
 
+#define MCTP_BINDS_BITS 7
+
 struct netns_mctp {
 	/* Only updated under RTNL, entries freed via RCU */
 	struct list_head routes;
 
-	/* Bound sockets: list of sockets bound by type.
-	 * This list is updated from non-atomic contexts (under bind_lock),
-	 * and read (under rcu) in packet rx
+	/* Bound sockets: hash table of sockets, keyed by
+	 * (type, src_eid, dest_eid).
+	 * Specific src_eid/dest_eid entries also have an entry for
+	 * MCTP_ADDR_ANY. This list is updated from non-atomic contexts
+	 * (under bind_lock), and read (under rcu) in packet rx.
 	 */
 	struct mutex bind_lock;
-	struct hlist_head binds;
+	DECLARE_HASHTABLE(binds, MCTP_BINDS_BITS);
 
 	/* tag allocations. This list is read and updated from atomic contexts,
 	 * but elements are free()ed after a RCU grace-period
@@ -34,4 +40,10 @@ struct netns_mctp {
 	struct list_head neighbours;
 };
 
+static inline u32 mctp_bind_hash(u8 type, u8 local_addr, u8 peer_addr)
+{
+	return hash_32(type | (u32)local_addr << 8 | (u32)peer_addr << 16,
+		       MCTP_BINDS_BITS);
+}
+
 #endif /* __NETNS_MCTP_H__ */

net/mctp/af_mctp.c

@@ -626,17 +626,17 @@ static int mctp_sk_hash(struct sock *sk)
 	struct net *net = sock_net(sk);
 	struct sock *existing;
 	struct mctp_sock *msk;
+	u32 hash;
 	int rc;
 
 	msk = container_of(sk, struct mctp_sock, sk);
 
-	/* Bind lookup runs under RCU, remain live during that. */
-	sock_set_flag(sk, SOCK_RCU_FREE);
+	hash = mctp_bind_hash(msk->bind_type, msk->bind_addr, MCTP_ADDR_ANY);
 
 	mutex_lock(&net->mctp.bind_lock);
 
 	/* Prevent duplicate binds. */
-	sk_for_each(existing, &net->mctp.binds) {
+	sk_for_each(existing, &net->mctp.binds[hash]) {
 		struct mctp_sock *mex =
 			container_of(existing, struct mctp_sock, sk);
 
@@ -648,7 +648,10 @@ static int mctp_sk_hash(struct sock *sk)
 		}
 	}
 
-	sk_add_node_rcu(sk, &net->mctp.binds);
+	/* Bind lookup runs under RCU, remain live during that. */
+	sock_set_flag(sk, SOCK_RCU_FREE);
+
+	sk_add_node_rcu(sk, &net->mctp.binds[hash]);
 	rc = 0;
 
 out:

net/mctp/route.c

@@ -40,14 +40,45 @@ static int mctp_dst_discard(struct mctp_dst *dst, struct sk_buff *skb)
 	return 0;
 }
 
-static struct mctp_sock *mctp_lookup_bind(struct net *net, struct sk_buff *skb)
+static struct mctp_sock *mctp_lookup_bind_details(struct net *net,
+						  struct sk_buff *skb,
+						  u8 type, u8 dest,
+						  u8 src, bool allow_net_any)
 {
 	struct mctp_skb_cb *cb = mctp_cb(skb);
-	struct mctp_hdr *mh;
 	struct sock *sk;
-	u8 type;
+	u8 hash;
 
-	WARN_ON(!rcu_read_lock_held());
+	WARN_ON_ONCE(!rcu_read_lock_held());
+
+	hash = mctp_bind_hash(type, dest, src);
+
+	sk_for_each_rcu(sk, &net->mctp.binds[hash]) {
+		struct mctp_sock *msk = container_of(sk, struct mctp_sock, sk);
+
+		if (!allow_net_any && msk->bind_net == MCTP_NET_ANY)
+			continue;
+
+		if (msk->bind_net != MCTP_NET_ANY && msk->bind_net != cb->net)
+			continue;
+
+		if (msk->bind_type != type)
+			continue;
+
+		if (!mctp_address_matches(msk->bind_addr, dest))
+			continue;
+
+		return msk;
+	}
+
+	return NULL;
+}
+
+static struct mctp_sock *mctp_lookup_bind(struct net *net, struct sk_buff *skb)
+{
+	struct mctp_sock *msk;
+	struct mctp_hdr *mh;
+	u8 type;
 
 	/* TODO: look up in skb->cb? */
 	mh = mctp_hdr(skb);
@@ -57,20 +88,36 @@ static struct mctp_sock *mctp_lookup_bind(struct net *net, struct sk_buff *skb)
 
 	type = (*(u8 *)skb->data) & 0x7f;
 
-	sk_for_each_rcu(sk, &net->mctp.binds) {
-		struct mctp_sock *msk = container_of(sk, struct mctp_sock, sk);
-
-		if (msk->bind_net != MCTP_NET_ANY && msk->bind_net != cb->net)
-			continue;
-
-		if (msk->bind_type != type)
-			continue;
-
-		if (!mctp_address_matches(msk->bind_addr, mh->dest))
-			continue;
+	/* Look for binds in order of widening scope. A given destination or
+	 * source address also implies matching on a particular network.
+	 *
+	 * - Matching destination and source
+	 * - Matching destination
+	 * - Matching source
+	 * - Matching network, any address
+	 * - Any network or address
+	 */
 
+	msk = mctp_lookup_bind_details(net, skb, type, mh->dest, mh->src,
+				       false);
+	if (msk)
+		return msk;
+	msk = mctp_lookup_bind_details(net, skb, type, MCTP_ADDR_ANY, mh->src,
+				       false);
+	if (msk)
+		return msk;
+	msk = mctp_lookup_bind_details(net, skb, type, mh->dest, MCTP_ADDR_ANY,
+				       false);
+	if (msk)
+		return msk;
+	msk = mctp_lookup_bind_details(net, skb, type, MCTP_ADDR_ANY,
+				       MCTP_ADDR_ANY, false);
+	if (msk)
+		return msk;
+	msk = mctp_lookup_bind_details(net, skb, type, MCTP_ADDR_ANY,
+				       MCTP_ADDR_ANY, true);
+	if (msk)
 		return msk;
-	}
 
 	return NULL;
 }
@@ -1671,7 +1718,7 @@ static int __net_init mctp_routes_net_init(struct net *net)
 	struct netns_mctp *ns = &net->mctp;
 
 	INIT_LIST_HEAD(&ns->routes);
-	INIT_HLIST_HEAD(&ns->binds);
+	hash_init(ns->binds);
 	mutex_init(&ns->bind_lock);
 	INIT_HLIST_HEAD(&ns->keys);
 	spin_lock_init(&ns->keys_lock);