Re: WARNING in hso_free_net_device

[Hui Peng]

Can you guys have a look at the attached patch?

On 9/4/19 6:41 PM, Stephen Hemminger wrote:
> On Wed, 4 Sep 2019 16:27:50 -0400
> Hui Peng <benquike@xxxxxxxxx> wrote:
>
>> Hi, all:
>>
>> I looked at the bug a little.
>>
>> The issue is that in the error handling code, hso_free_net_device
>> unregisters
>>
>> the net_device (hso_net->net)Â by calling unregister_netdev. In the
>> error handling code path,
>>
>> hso_net->net has not been registered yet.
>>
>> I think there are two ways to solve the issue:
>>
>> 1. fix it in drivers/net/usb/hso.c to avoiding unregistering the
>> net_device when it is still not registered
>>
>> 2. fix it in unregister_netdev. We can add a field in net_device to
>> record whether it is registered, and make unregister_netdev return if
>> the net_device is not registered yet.
>>
>> What do you guys think ?
> #1
From f3fdee8fc03aa2bc982f22da1d29bbf6bca72935 Mon Sep 17 00:00:00 2001
From: Hui Peng <benquike@xxxxxxxxx>
Date: Wed, 4 Sep 2019 21:38:35 -0400
Subject: [PATCH] Fix a wrong unregistering bug in hso_free_net_device

As shown below, hso_create_net_device may call hso_free_net_device
before the net_device is registered. hso_free_net_device will
unregister the network device no matter it is registered or not,
unregister_netdev is not able to handle unregistered net_device,
resulting in the bug reported by the syzbot.

```
static struct hso_device *hso_create_net_device(struct usb_interface *interface,
					       int port_spec)
{
	......
	net = alloc_netdev(sizeof(struct hso_net), "hso%d", NET_NAME_UNKNOWN,
      			    hso_net_init);
	......
	if (!hso_net->out_endp) {
   	   	dev_err(&interface->dev, "Can't find BULK OUT endpoint\n");
		goto exit;
	}

	......
	result = register_netdev(net);
	......
exit:
	hso_free_net_device(hso_dev);
	return NULL;
}

static void hso_free_net_device(struct hso_device *hso_dev)
{
	......
	if (hso_net->net)
		unregister_netdev(hso_net->net);
	......
}

```

This patch adds a net_registered field in struct hso_net to record whether
the containing net_device is registered or not, and avoid unregistering it
if it is not registered yet.

Reported-by: syzbot+44d53c7255bb1aea22d2@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Hui Peng <benquike@xxxxxxxxx>
---
 drivers/net/usb/hso.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/usb/hso.c b/drivers/net/usb/hso.c
index ce78714..5b3df33 100644
--- a/drivers/net/usb/hso.c
+++ b/drivers/net/usb/hso.c
@@ -128,6 +128,7 @@ struct hso_shared_int {
 struct hso_net {
 	struct hso_device *parent;
 	struct net_device *net;
+	bool net_registered;
 	struct rfkill *rfkill;
 	char name[24];
 
@@ -2362,7 +2363,7 @@ static void hso_free_net_device(struct hso_device *hso_dev)
 
 	remove_net_device(hso_net->parent);
 
-	if (hso_net->net)
+	if (hso_net->net && hso_net->net_registered)
 		unregister_netdev(hso_net->net);
 
 	/* start freeing */
@@ -2544,6 +2545,7 @@ static struct hso_device *hso_create_net_device(struct usb_interface *interface,
 		dev_err(&interface->dev, "Failed to register device\n");
 		goto exit;
 	}
+	hso_net->net_registered = true;
 
 	hso_log_port(hso_dev);
 
-- 
2.7.4

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