netdev - [PATCH net-next 2/7] net: mctp: Treat MCTP_NET

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Message-Id: <20250703-mctp-bind-v1-2-bb7e97c24613@codeconstruct.com.au>
Date: Thu, 03 Jul 2025 17:11:49 +0800
From: Matt Johnston <matt@...econstruct.com.au>
To: Jeremy Kerr <jk@...econstruct.com.au>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Simon Horman <horms@...nel.org>
Cc: netdev@...r.kernel.org, Matt Johnston <matt@...econstruct.com.au>
Subject: [PATCH net-next 2/7] net: mctp: Treat MCTP_NET_ANY specially in
 bind()

When a specific EID is passed as a bind address, it only makes sense to
interpret with an actual network ID, so resolve that to the default
network at bind time.

For bind address of MCTP_ADDR_ANY, we want to be able to capture traffic
to any network and address, so keep the current behaviour of matching
traffic from any network interface (don't interpret MCTP_NET_ANY as
the default network ID).

Signed-off-by: Matt Johnston <matt@...econstruct.com.au>
---
 net/mctp/af_mctp.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/net/mctp/af_mctp.c b/net/mctp/af_mctp.c
index 72ab8449ebfc68f6b7a9954cbf13a7be00543358..4751f5fc082dcab27df77a9c5acbc6abb4e861d5 100644
--- a/net/mctp/af_mctp.c
+++ b/net/mctp/af_mctp.c
@@ -53,6 +53,7 @@ static int mctp_bind(struct socket *sock, struct sockaddr *addr, int addrlen)
 {
 	struct sock *sk = sock->sk;
 	struct mctp_sock *msk = container_of(sk, struct mctp_sock, sk);
+	struct net *net = sock_net(&msk->sk);
 	struct sockaddr_mctp *smctp;
 	int rc;

@@ -77,8 +78,20 @@ static int mctp_bind(struct socket *sock, struct sockaddr *addr, int addrlen)
 		rc = -EADDRINUSE;
 		goto out_release;
 	}
-	msk->bind_net = smctp->smctp_network;
+
 	msk->bind_addr = smctp->smctp_addr.s_addr;
+
+	/* MCTP_NET_ANY with a specific EID is resolved to the default net
+	 * at bind() time.
+	 * For bind_addr=MCTP_ADDR_ANY it is handled specially at route lookup time.
+	 */
+	if (smctp->smctp_network == MCTP_NET_ANY &&
+	    msk->bind_addr != MCTP_ADDR_ANY) {
+		msk->bind_net = mctp_default_net(net);
+	} else {
+		msk->bind_net = smctp->smctp_network;
+	}
+
 	msk->bind_type = smctp->smctp_type & 0x7f; /* ignore the IC bit */

 	rc = sk->sk_prot->hash(sk);

-- 
2.43.0