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Date:   Sun, 22 Nov 2020 08:12:56 +0200
From:   Parav Pandit <parav@...dia.com>
To:     <kuba@...nel.org>, <davem@...emloft.net>, <netdev@...r.kernel.org>,
        <jiri@...dia.com>
CC:     Parav Pandit <parav@...dia.com>
Subject: [PATCH net 1/2] devlink: Hold rtnl lock while reading netdev attributes

A netdevice of a devlink port can be moved to different
net namespace than its parent devlink instance.
This scenario occurs when devlink reload is not used for
maintaining backward compatibility.

When netdevice is undergoing migration to net namespace,
its ifindex and name may change.

In such use case, devlink port query may read stale netdev
attributes.

Fix it by reading them under rtnl lock.

Fixes: bfcd3a466172 ("Introduce devlink infrastructure")
Signed-off-by: Parav Pandit <parav@...dia.com>
---
 net/core/devlink.c | 30 ++++++++++++++++++++++++------
 1 file changed, 24 insertions(+), 6 deletions(-)

diff --git a/net/core/devlink.c b/net/core/devlink.c
index acc29d5157f4..6135ef5972ce 100644
--- a/net/core/devlink.c
+++ b/net/core/devlink.c
@@ -775,6 +775,23 @@ devlink_nl_port_function_attrs_put(struct sk_buff *msg, struct devlink_port *por
 	return err;
 }
 
+static int devlink_nl_port_netdev_fill(struct sk_buff *msg, struct devlink_port *devlink_port)
+{
+	struct net_device *netdev = devlink_port->type_dev;
+	int err;
+
+	ASSERT_RTNL();
+	if (!netdev)
+		return 0;
+
+	err = nla_put_u32(msg, DEVLINK_ATTR_PORT_NETDEV_IFINDEX, netdev->ifindex);
+	if (err)
+		goto done;
+	err = nla_put_string(msg, DEVLINK_ATTR_PORT_NETDEV_NAME, netdev->name);
+done:
+	return err;
+}
+
 static int devlink_nl_port_fill(struct sk_buff *msg, struct devlink *devlink,
 				struct devlink_port *devlink_port,
 				enum devlink_command cmd, u32 portid,
@@ -792,6 +809,8 @@ static int devlink_nl_port_fill(struct sk_buff *msg, struct devlink *devlink,
 	if (nla_put_u32(msg, DEVLINK_ATTR_PORT_INDEX, devlink_port->index))
 		goto nla_put_failure;
 
+	/* Hold rtnl lock while accessing port's netdev attributes. */
+	rtnl_lock();
 	spin_lock_bh(&devlink_port->type_lock);
 	if (nla_put_u16(msg, DEVLINK_ATTR_PORT_TYPE, devlink_port->type))
 		goto nla_put_failure_type_locked;
@@ -800,13 +819,10 @@ static int devlink_nl_port_fill(struct sk_buff *msg, struct devlink *devlink,
 			devlink_port->desired_type))
 		goto nla_put_failure_type_locked;
 	if (devlink_port->type == DEVLINK_PORT_TYPE_ETH) {
-		struct net_device *netdev = devlink_port->type_dev;
+		int err;
 
-		if (netdev &&
-		    (nla_put_u32(msg, DEVLINK_ATTR_PORT_NETDEV_IFINDEX,
-				 netdev->ifindex) ||
-		     nla_put_string(msg, DEVLINK_ATTR_PORT_NETDEV_NAME,
-				    netdev->name)))
+		err = devlink_nl_port_netdev_fill(msg, devlink_port);
+		if (err)
 			goto nla_put_failure_type_locked;
 	}
 	if (devlink_port->type == DEVLINK_PORT_TYPE_IB) {
@@ -818,6 +834,7 @@ static int devlink_nl_port_fill(struct sk_buff *msg, struct devlink *devlink,
 			goto nla_put_failure_type_locked;
 	}
 	spin_unlock_bh(&devlink_port->type_lock);
+	rtnl_unlock();
 	if (devlink_nl_port_attrs_put(msg, devlink_port))
 		goto nla_put_failure;
 	if (devlink_nl_port_function_attrs_put(msg, devlink_port, extack))
@@ -828,6 +845,7 @@ static int devlink_nl_port_fill(struct sk_buff *msg, struct devlink *devlink,
 
 nla_put_failure_type_locked:
 	spin_unlock_bh(&devlink_port->type_lock);
+	rtnl_unlock();
 nla_put_failure:
 	genlmsg_cancel(msg, hdr);
 	return -EMSGSIZE;
-- 
2.26.2

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