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Subject: Re: WARNING in hso_free_net_device
To:     Stephen Hemminger <stephen@networkplumber.org>
Cc:     syzbot+44d53c7255bb1aea22d2@syzkaller.appspotmail.com,
        alexios.zavras@intel.com, andreyknvl@google.com,
        davem@davemloft.net, gregkh@linuxfoundation.org,
        linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org,
        mathias.payer@nebelwelt.net, netdev@vger.kernel.org,
        rfontana@redhat.com, syzkaller-bugs@googlegroups.com,
        tglx@linutronix.de
References: <0000000000002a95df0591a4f114@google.com>
 <d6e4d2da-66c6-a8fe-2fea-a3435fa7cb54@gmail.com>
 <20190904154140.45dfb398@hermes.lan>
From:   Hui Peng <benquike@gmail.com>
Message-ID: <285edb24-01f9-3f9d-4946-b2f41ccd0774@gmail.com>
Date:   Wed, 4 Sep 2019 22:20:23 -0400
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Can you guys have=C2=A0 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@gmail.com> 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)=C2=A0 by calling unregister_netdev. In t=
he
>> 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

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 name="0001-Fix-a-wrong-unregistering-bug-in-hso_free_net_device.patch"
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=46rom f3fdee8fc03aa2bc982f22da1d29bbf6bca72935 Mon Sep 17 00:00:00 2001
From: Hui Peng <benquike@gmail.com>
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 *int=
erface,
					       int port_spec)
{
	......
	net =3D 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 =3D 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 whethe=
r
the containing net_device is registered or not, and avoid unregistering i=
t
if it is not registered yet.

Reported-by: syzbot+44d53c7255bb1aea22d2@syzkaller.appspotmail.com
Signed-off-by: Hui Peng <benquike@gmail.com>
---
 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];
=20
@@ -2362,7 +2363,7 @@ static void hso_free_net_device(struct hso_device *=
hso_dev)
=20
 	remove_net_device(hso_net->parent);
=20
-	if (hso_net->net)
+	if (hso_net->net && hso_net->net_registered)
 		unregister_netdev(hso_net->net);
=20
 	/* start freeing */
@@ -2544,6 +2545,7 @@ static struct hso_device *hso_create_net_device(str=
uct usb_interface *interface,
 		dev_err(&interface->dev, "Failed to register device\n");
 		goto exit;
 	}
+	hso_net->net_registered =3D true;
=20
 	hso_log_port(hso_dev);
=20
--=20
2.7.4


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