net: mctp: allow local TX with no address assigned

If we're operating as a non-bus-owner endpoint, we may want to perform
MCTP communication to get an address assigned. In this case, we'll have
no local addresses, but can TX just fine either with extended routing,
or where a direct route exists.

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>
Link: https://patch.msgid.link/20260331-dev-mctp-null-eids-v1-2-b4d047372eaf@codeconstruct.com.au
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

2 files changed, 118 insertions, 14 deletions

diff --git a/net/mctp/route.c b/net/mctp/route.c
index f6a88e668e68..8c484776e9e4 100644
--- a/net/mctp/route.c
+++ b/net/mctp/route.c
@@ -997,8 +997,8 @@ int mctp_route_lookup(struct net *net, unsigned int dnet,
 
 		if (rt->dst_type == MCTP_ROUTE_DIRECT) {
 			mctp_dst_from_route(&dst_tmp, daddr, mtu, rt);
-			/* we need a source address */
-			if (dst_tmp.saddr == MCTP_ADDR_NULL) {
+			/* cannot do gateway-ed routes without a src  */
+			if (dst_tmp.saddr == MCTP_ADDR_NULL && depth != 0) {
 				mctp_dst_release(&dst_tmp);
 			} else {
 				if (dst)
@@ -1141,19 +1141,13 @@ int mctp_local_output(struct sock *sk, struct mctp_dst *dst,
 	struct mctp_sk_key *key;
 	struct mctp_hdr *hdr;
 	unsigned int netid;
-	int rc = 0;
 	u8 tag;
 
 	KUNIT_STATIC_STUB_REDIRECT(mctp_local_output, sk, dst, skb, daddr,
 				   req_tag);
 
-	if (dst->saddr == MCTP_ADDR_NULL)
-		rc = -EHOSTUNREACH;
 	netid = READ_ONCE(dst->dev->net);
 
-	if (rc)
-		goto err_free;
-
 	if (req_tag & MCTP_TAG_OWNER) {
 		if (req_tag & MCTP_TAG_PREALLOC)
 			key = mctp_lookup_prealloc_tag(msk, netid, daddr,
@@ -1163,8 +1157,8 @@ int mctp_local_output(struct sock *sk, struct mctp_dst *dst,
 						   daddr, false, &tag);
 
 		if (IS_ERR(key)) {
-			rc = PTR_ERR(key);
-			goto err_free;
+			kfree_skb(skb);
+			return PTR_ERR(key);
 		}
 		mctp_skb_set_flow(skb, key);
 		/* done with the key in this scope */
@@ -1191,10 +1185,6 @@ int mctp_local_output(struct sock *sk, struct mctp_dst *dst,
 
 	/* route output functions consume the skb, even on error */
 	return mctp_do_fragment_route(dst, skb, dst->mtu, tag);
-
-err_free:
-	kfree_skb(skb);
-	return rc;
 }
 
 /* route management */
diff --git a/net/mctp/test/route-test.c b/net/mctp/test/route-test.c
index 639b7c41c2a2..fa28af9ac18e 100644
--- a/net/mctp/test/route-test.c
+++ b/net/mctp/test/route-test.c
@@ -1570,6 +1570,117 @@ cleanup:
 	__mctp_route_test_fini(test, dev, &dst, sock_ty0);
 }
 
+static void mctp_test_route_output_direct_no_eids(struct kunit *test)
+{
+	struct mctp_dst dst = { 0 };
+	struct sk_buff *skb, *skb2;
+	struct mctp_test_route *rt;
+	struct mctp_test_dev *dev;
+	struct socket *sock;
+	const int len = 2;
+	int rc;
+
+	dev = mctp_test_create_dev();
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, dev);
+
+	rt = mctp_test_create_route_direct(&init_net, dev->mdev, 9, 68);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, rt);
+
+	rc = mctp_route_lookup(&init_net, dev->mdev->net, 9, &dst);
+	KUNIT_ASSERT_EQ(test, rc, 0);
+
+	rc = sock_create_kern(&init_net, AF_MCTP, SOCK_DGRAM, 0, &sock);
+	KUNIT_ASSERT_EQ(test, rc, 0);
+
+	skb = alloc_skb(sizeof(struct mctp_hdr) + 1 + len, GFP_KERNEL);
+	KUNIT_ASSERT_TRUE(test, skb);
+	__mctp_cb(skb);
+	skb_reserve(skb, sizeof(struct mctp_hdr) + 1 + len);
+	memset(skb_put(skb, len), 0, len);
+
+	rc = mctp_local_output(sock->sk, &dst, skb, 9, MCTP_TAG_OWNER);
+	KUNIT_ASSERT_EQ(test, rc, 0);
+
+	KUNIT_ASSERT_EQ(test, dev->pkts.qlen, 1);
+
+	skb2 = skb_dequeue(&dev->pkts);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, skb2);
+
+	kfree_skb(skb2);
+	sock_release(sock);
+	mctp_dst_release(&dst);
+	mctp_test_route_destroy(test, rt);
+	mctp_test_destroy_dev(dev);
+}
+
+static void mctp_test_route_output_gw_no_eids(struct kunit *test)
+{
+	struct mctp_test_route *rt1, *rt2;
+	struct mctp_test_dev *dev;
+	struct mctp_dst dst = { 0 };
+	int rc;
+
+	dev = mctp_test_create_dev();
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, dev);
+
+	/* route: direct to bridge */
+	rt1 = mctp_test_create_route_direct(&init_net, dev->mdev, 9, 68);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, rt1);
+
+	/* route: bridge gw to final dest */
+	rt2 = mctp_test_create_route_gw(&init_net, dev->mdev->net, 10, 9, 0);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, rt2);
+
+	/* route lookup should fail, due to no source address on dev */
+	rc = mctp_route_lookup(&init_net, dev->mdev->net, 10, &dst);
+	KUNIT_ASSERT_NE(test, rc, 0);
+
+	mctp_test_route_destroy(test, rt1);
+	mctp_test_route_destroy(test, rt2);
+	mctp_test_destroy_dev(dev);
+}
+
+static void mctp_test_route_output_extaddr_no_eids(struct kunit *test)
+{
+	struct mctp_dst dst = { 0 };
+	struct sk_buff *skb, *skb2;
+	struct mctp_test_dev *dev;
+	struct socket *sock;
+	const int len = 1;
+	struct net *net;
+	int rc;
+
+	dev = mctp_test_create_dev();
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, dev);
+
+	net = dev_net(dev->ndev);
+
+	rc = mctp_dst_from_extaddr(&dst, net, dev->ndev->ifindex, 0, NULL);
+	KUNIT_ASSERT_EQ(test, rc, 0);
+
+	rc = sock_create_kern(net, AF_MCTP, SOCK_DGRAM, 0, &sock);
+	KUNIT_ASSERT_EQ(test, rc, 0);
+
+	skb = alloc_skb(sizeof(struct mctp_hdr) + 1 + len, GFP_KERNEL);
+	KUNIT_ASSERT_TRUE(test, skb);
+	__mctp_cb(skb);
+	skb_reserve(skb, sizeof(struct mctp_hdr) + 1 + len);
+	memset(skb_put(skb, len), 0, len);
+
+	rc = mctp_local_output(sock->sk, &dst, skb, 9, MCTP_TAG_OWNER);
+	KUNIT_ASSERT_EQ(test, rc, 0);
+
+	KUNIT_ASSERT_EQ(test, dev->pkts.qlen, 1);
+
+	skb2 = skb_dequeue(&dev->pkts);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, skb2);
+
+	kfree_skb(skb2);
+	sock_release(sock);
+	mctp_dst_release(&dst);
+	mctp_test_destroy_dev(dev);
+}
+
 static struct kunit_case mctp_test_cases[] = {
 	KUNIT_CASE_PARAM(mctp_test_fragment, mctp_frag_gen_params),
 	KUNIT_CASE_PARAM(mctp_test_rx_input, mctp_rx_input_gen_params),
@@ -1592,6 +1703,9 @@ static struct kunit_case mctp_test_cases[] = {
 	KUNIT_CASE_PARAM(mctp_test_route_gw_mtu, mctp_route_gw_mtu_gen_params),
 	KUNIT_CASE(mctp_test_route_gw_output),
 	KUNIT_CASE_PARAM(mctp_test_bind_lookup, mctp_bind_lookup_gen_params),
+	KUNIT_CASE(mctp_test_route_output_direct_no_eids),
+	KUNIT_CASE(mctp_test_route_output_gw_no_eids),
+	KUNIT_CASE(mctp_test_route_output_extaddr_no_eids),
 	{}
 };