[PATCH v5 08/11] net: qrtr: allow socket endpoint binding

[Mihai Moldovan <ionic@ionic.de>]

From: Denis Kenzior <denkenz@gmail.com>

Introduce the ability to bind a QIPCRTR family socket to a specific
endpoint.  When a socket is bound, only messages from the bound
endpoint can be received, and any messages sent from the socket are
by default directed to the bound endpoint.  Clients can bind a socket
by using the setsockopt system call with the QRTR_BIND_ENDPOINT option
set to the desired endpoint binding.

A previously set binding can be reset by setting QRTR_BIND_ENDPOINT
option to zero.  This behavior matches that of SO_BINDTOIFINDEX.

This functionality is useful for clients that need to communicate
with a specific device (i.e. endpoint), such as a PCIe-based 5G modem,
and are not interested in messages from other endpoints / nodes.

Signed-off-by: Denis Kenzior <denkenz@gmail.com>
Reviewed-by: Marcel Holtmann <marcel@holtmann.org>
Reviewed-by: Andy Gross <agross@kernel.org>
Signed-off-by: Mihai Moldovan <ionic@ionic.de>

---
v5:
  - no changes
  - Link to v4: https://msgid.link/d8e917f8083f2d6041681f2f6683bc5f53a185e6.1753720935.git.ionic@ionic.de

v4:
  - rebase against earlier changes
  - Link to v3: https://msgid.link/b523ece3e16dc4c8a9acf740aba5270227a2a2b8.1753313000.git.ionic@ionic.de

v3:
  - rebase against current master
  - Link to v2: https://msgid.link/c914eae5bd8d4a3924cc3c00c1dd5810024678f5.1752947108.git.ionic@ionic.de

v2:
  - rebase against current master
  - use WRITE_ONCE() to write value in qrtr_setsockopt() and READ_ONCE()
    to read it in qrtr_getsockopt() as per review comment
  - Link to v1: https://msgid.link/20241018181842.1368394-8-denkenz@gmail.com
---
 include/uapi/linux/qrtr.h |  1 +
 net/qrtr/af_qrtr.c        | 56 ++++++++++++++++++++++++++++-----------
 2 files changed, 41 insertions(+), 16 deletions(-)

diff --git a/include/uapi/linux/qrtr.h b/include/uapi/linux/qrtr.h
index 6d0911984a05..0a8667b049c3 100644
--- a/include/uapi/linux/qrtr.h
+++ b/include/uapi/linux/qrtr.h
@@ -48,6 +48,7 @@ struct qrtr_ctrl_pkt {
 
 /* setsockopt / getsockopt */
 #define QRTR_REPORT_ENDPOINT 1
+#define QRTR_BIND_ENDPOINT 2
 
 /* CMSG */
 #define QRTR_ENDPOINT 1
diff --git a/net/qrtr/af_qrtr.c b/net/qrtr/af_qrtr.c
index fa88a8ed4d8c..a7ab445416e4 100644
--- a/net/qrtr/af_qrtr.c
+++ b/net/qrtr/af_qrtr.c
@@ -98,6 +98,7 @@ struct qrtr_sock {
 	struct sockaddr_qrtr us;
 	struct sockaddr_qrtr peer;
 	unsigned long flags;
+	u32 bound_endpoint;
 };
 
 static inline struct qrtr_sock *qrtr_sk(struct sock *sk)
@@ -664,10 +665,14 @@ int qrtr_endpoint_post(struct qrtr_endpoint *ep, const void *data, size_t len)
 			goto err;
 		}
 
-		ret = sock_queue_rcv_skb(&ipc->sk, skb);
-		if (ret) {
-			qrtr_port_put(ipc);
-			goto err;
+		/* Sockets bound to an endpoint only rx from that endpoint */
+		if (!ipc->bound_endpoint ||
+		    ipc->bound_endpoint == cb->endpoint_id) {
+			ret = sock_queue_rcv_skb(&ipc->sk, skb);
+			if (ret) {
+				qrtr_port_put(ipc);
+				goto err;
+			}
 		}
 
 		qrtr_port_put(ipc);
@@ -1008,29 +1013,41 @@ static int qrtr_local_enqueue(struct qrtr_node *node, struct sk_buff *skb,
 {
 	struct qrtr_sock *ipc;
 	struct qrtr_cb *cb;
+	int ret = -ENODEV;
 
 	ipc = qrtr_port_lookup(to->sq_port);
-	if (!ipc || &ipc->sk == skb->sk) { /* do not send to self */
-		if (ipc)
-			qrtr_port_put(ipc);
-		kfree_skb(skb);
-		return -ENODEV;
-	}
+	if (!ipc)
+		goto done;
+
+	if (&ipc->sk == skb->sk) /* do not send to self */
+		goto done;
+
+	/*
+	 * Filter out unwanted packets that are not on behalf of the bound
+	 * endpoint.  Certain special packets (such as an empty NEW_SERVER
+	 * packet that serves as a sentinel value) always go through.
+	 */
+	if (endpoint_id && ipc->bound_endpoint &&
+	    ipc->bound_endpoint != endpoint_id)
+		goto done;
 
 	cb = (struct qrtr_cb *)skb->cb;
 	cb->src_node = from->sq_node;
 	cb->src_port = from->sq_port;
 	cb->endpoint_id = endpoint_id;
 
-	if (sock_queue_rcv_skb(&ipc->sk, skb)) {
-		qrtr_port_put(ipc);
-		kfree_skb(skb);
-		return -ENOSPC;
-	}
+	ret = -ENOSPC;
+	if (sock_queue_rcv_skb(&ipc->sk, skb))
+		goto done;
 
 	qrtr_port_put(ipc);
 
 	return 0;
+done:
+	if (ipc)
+		qrtr_port_put(ipc);
+	kfree_skb(skb);
+	return ret;
 }
 
 /* Queue packet for broadcast. */
@@ -1116,7 +1133,8 @@ static int qrtr_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
 	} else if (addr->sq_node == ipc->us.sq_node) {
 		enqueue_fn = qrtr_local_enqueue;
 	} else {
-		endpoint_id = msg_endpoint_id;
+		endpoint_id = msg_endpoint_id ?
+			      msg_endpoint_id : ipc->bound_endpoint;
 
 		node = qrtr_node_lookup(endpoint_id, addr->sq_node);
 		if (!node) {
@@ -1392,6 +1410,9 @@ static int qrtr_setsockopt(struct socket *sock, int level, int optname,
 	case QRTR_REPORT_ENDPOINT:
 		assign_bit(QRTR_F_REPORT_ENDPOINT, &ipc->flags, val);
 		break;
+	case QRTR_BIND_ENDPOINT:
+		WRITE_ONCE(ipc->bound_endpoint, val);
+		break;
 	default:
 		rc = -ENOPROTOOPT;
 	}
@@ -1420,6 +1441,9 @@ static int qrtr_getsockopt(struct socket *sock, int level, int optname,
 	case QRTR_REPORT_ENDPOINT:
 		val = test_bit(QRTR_F_REPORT_ENDPOINT, &ipc->flags);
 		break;
+	case QRTR_BIND_ENDPOINT:
+		val = READ_ONCE(ipc->bound_endpoint);
+		break;
 	default:
 		rc = -ENOPROTOOPT;
 	}
-- 
2.50.0