hv_netvsc: Fix a memory leak bug

In rndis_filter_device_add(), 'rndis_device' is allocated through kzalloc()
by invoking get_rndis_device(). In the following execution, if an error
occurs, the execution will go to the 'err_dev_remv' label. However, the
allocated 'rndis_device' is not deallocated, leading to a memory leak bug.

Signed-off-by: Wenwen Wang <wenwen@cs.uga.edu>
---
 drivers/net/hyperv/rndis_filter.c | 1 +
 1 file changed, 1 insertion(+)

> -----Original Message-----
> From: Wenwen Wang <wenwen@cs.uga.edu>
> Sent: Wednesday, August 14, 2019 4:16 PM
> To: Wenwen Wang <wenwen@cs.uga.edu>
> Cc: KY Srinivasan <kys@microsoft.com>; Haiyang Zhang
> <haiyangz@microsoft.com>; Stephen Hemminger
> <sthemmin@microsoft.com>; Sasha Levin <sashal@kernel.org>; David S.
> Miller <davem@davemloft.net>; open list:Hyper-V CORE AND DRIVERS
> <linux-hyperv@vger.kernel.org>; open list:NETWORKING DRIVERS
> <netdev@vger.kernel.org>; open list <linux-kernel@vger.kernel.org>
> Subject: [PATCH] hv_netvsc: Fix a memory leak bug
> 
> In rndis_filter_device_add(), 'rndis_device' is allocated through kzalloc()
> by invoking get_rndis_device(). In the following execution, if an error
> occurs, the execution will go to the 'err_dev_remv' label. However, the
> allocated 'rndis_device' is not deallocated, leading to a memory leak bug.
> 
> Signed-off-by: Wenwen Wang <wenwen@cs.uga.edu>
> ---
>  drivers/net/hyperv/rndis_filter.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/net/hyperv/rndis_filter.c
> b/drivers/net/hyperv/rndis_filter.c
> index 317dbe9..ed35085 100644
> --- a/drivers/net/hyperv/rndis_filter.c
> +++ b/drivers/net/hyperv/rndis_filter.c
> @@ -1420,6 +1420,7 @@ struct netvsc_device
> *rndis_filter_device_add(struct hv_device *dev,
> 
>  err_dev_remv:
>  	rndis_filter_device_remove(dev, net_device);
> +	kfree(rndis_device);

The kfree() is not necessary here. 
Because it is already freed by --
rndis_filter_device_remove() --> netvsc_device_remove() 
--> free_netvsc_device_rcu() --> free_netvsc_device()
--> kfree(nvdev->extension);  //This frees rndis_device.

Thanks,
- Haiyang

On Wed, 14 Aug 2019 15:16:11 -0500
Wenwen Wang <wenwen@cs.uga.edu> wrote:

> In rndis_filter_device_add(), 'rndis_device' is allocated through kzalloc()
> by invoking get_rndis_device(). In the following execution, if an error
> occurs, the execution will go to the 'err_dev_remv' label. However, the
> allocated 'rndis_device' is not deallocated, leading to a memory leak bug.
> 
> Signed-off-by: Wenwen Wang <wenwen@cs.uga.edu>
> ---
>  drivers/net/hyperv/rndis_filter.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/net/hyperv/rndis_filter.c b/drivers/net/hyperv/rndis_filter.c
> index 317dbe9..ed35085 100644
> --- a/drivers/net/hyperv/rndis_filter.c
> +++ b/drivers/net/hyperv/rndis_filter.c
> @@ -1420,6 +1420,7 @@ struct netvsc_device *rndis_filter_device_add(struct hv_device *dev,
>  
>  err_dev_remv:
>  	rndis_filter_device_remove(dev, net_device);
> +	kfree(rndis_device);
>  	return ERR_PTR(ret);
>  }
>  

The rndis_device is already freed by:

rndis_filter_device_remove
	netvsc_device_remove
		free_netvsc_device_rcu

free_netvsc_device called by rcu

static void free_netvsc_device(struct rcu_head *head)
{
	struct netvsc_device *nvdev
		= container_of(head, struct netvsc_device, rcu);
	int i;

	kfree(nvdev->extension);  << here