[PATCH RFC] RDMA/siw: Fabricate a GID on tun and loopback devices

[Chuck Lever <cel@kernel.org>]

From: Chuck Lever <chuck.lever@oracle.com>

LOOPBACK and NONE (tunnel) devices have all-zero MAC addresses.
Currently, siw_device_create() falls back to copying the IB device's
name in those cases, because an all-zero MAC address breaks the RDMA
core address resolution mechanism.

However, at the point when siw_device_create() constructs a GID, the
ib_device::name field is uninitialized, leaving the MAC address to
remain in an all-zero state.

Fabricate a random artificial GID for such devices, and ensure that
artificial GID is returned for all device query operations.

Reported-by: Tom Talpey <tom@talpey.com>
Link: https://lore.kernel.org/linux-rdma/SA0PR15MB391986C07C4D41E107E79659994FA@SA0PR15MB3919.namprd15.prod.outlook.com/T/#t
Fixes: a2d36b02c15d ("RDMA/siw: Enable siw on tunnel devices")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 drivers/infiniband/sw/siw/siw.h       |    1 +
 drivers/infiniband/sw/siw/siw_main.c  |   22 ++++++++--------------
 drivers/infiniband/sw/siw/siw_verbs.c |    4 ++--
 3 files changed, 11 insertions(+), 16 deletions(-)

diff --git a/drivers/infiniband/sw/siw/siw.h b/drivers/infiniband/sw/siw/siw.h
index d7f5b2a8669d..41fb8976abc6 100644
--- a/drivers/infiniband/sw/siw/siw.h
+++ b/drivers/infiniband/sw/siw/siw.h
@@ -74,6 +74,7 @@ struct siw_device {
 
 	u32 vendor_part_id;
 	int numa_node;
+	char raw_gid[ETH_ALEN];
 
 	/* physical port state (only one port per device) */
 	enum ib_port_state state;
diff --git a/drivers/infiniband/sw/siw/siw_main.c b/drivers/infiniband/sw/siw/siw_main.c
index 1225ca613f50..57896fafa6c0 100644
--- a/drivers/infiniband/sw/siw/siw_main.c
+++ b/drivers/infiniband/sw/siw/siw_main.c
@@ -75,8 +75,7 @@ static int siw_device_register(struct siw_device *sdev, const char *name)
 		return rv;
 	}
 
-	siw_dbg(base_dev, "HWaddr=%pM\n", sdev->netdev->dev_addr);
-
+	siw_dbg(base_dev, "HWaddr=%pM\n", sdev->raw_gid);
 	return 0;
 }
 
@@ -314,24 +313,19 @@ static struct siw_device *siw_device_create(struct net_device *netdev)
 		return NULL;
 
 	base_dev = &sdev->base_dev;
-
 	sdev->netdev = netdev;
 
-	if (netdev->type != ARPHRD_LOOPBACK && netdev->type != ARPHRD_NONE) {
-		addrconf_addr_eui48((unsigned char *)&base_dev->node_guid,
-				    netdev->dev_addr);
+	if (netdev->addr_len) {
+		memcpy(sdev->raw_gid, netdev->dev_addr,
+		       min_t(unsigned int, netdev->addr_len, ETH_ALEN));
 	} else {
 		/*
-		 * This device does not have a HW address,
-		 * but connection mangagement lib expects gid != 0
+		 * This device does not have a HW address, but
+		 * connection mangagement requires a unique gid.
 		 */
-		size_t len = min_t(size_t, strlen(base_dev->name), 6);
-		char addr[6] = { };
-
-		memcpy(addr, base_dev->name, len);
-		addrconf_addr_eui48((unsigned char *)&base_dev->node_guid,
-				    addr);
+		eth_random_addr(sdev->raw_gid);
 	}
+	addrconf_addr_eui48((u8 *)&base_dev->node_guid, sdev->raw_gid);
 
 	base_dev->uverbs_cmd_mask |= BIT_ULL(IB_USER_VERBS_CMD_POST_SEND);
 
diff --git a/drivers/infiniband/sw/siw/siw_verbs.c b/drivers/infiniband/sw/siw/siw_verbs.c
index 398ec13db624..32b0befd25e2 100644
--- a/drivers/infiniband/sw/siw/siw_verbs.c
+++ b/drivers/infiniband/sw/siw/siw_verbs.c
@@ -157,7 +157,7 @@ int siw_query_device(struct ib_device *base_dev, struct ib_device_attr *attr,
 	attr->vendor_part_id = sdev->vendor_part_id;
 
 	addrconf_addr_eui48((u8 *)&attr->sys_image_guid,
-			    sdev->netdev->dev_addr);
+			    sdev->raw_gid);
 
 	return 0;
 }
@@ -218,7 +218,7 @@ int siw_query_gid(struct ib_device *base_dev, u32 port, int idx,
 
 	/* subnet_prefix == interface_id == 0; */
 	memset(gid, 0, sizeof(*gid));
-	memcpy(&gid->raw[0], sdev->netdev->dev_addr, 6);
+	memcpy(gid->raw, sdev->raw_gid, ETH_ALEN);
 
 	return 0;
 }