[v2] hv_netvsc: Fix memory leak when removing rndis device

kmemleak detects the following memory leak when hot removing
a network device:

unreferenced object 0xffff888083f63600 (size 256):
  comm "kworker/0:1", pid 12, jiffies 4294831717 (age 1113.676s)
  hex dump (first 32 bytes):
    00 40 c7 33 80 88 ff ff 00 00 00 00 10 00 00 00  .@.3............
    00 00 00 00 ad 4e ad de ff ff ff ff 00 00 00 00  .....N..........
  backtrace:
    [<00000000d4a8f5be>] rndis_filter_device_add+0x117/0x11c0 [hv_netvsc]
    [<000000009c02d75b>] netvsc_probe+0x5e7/0xbf0 [hv_netvsc]
    [<00000000ddafce23>] vmbus_probe+0x74/0x170 [hv_vmbus]
    [<00000000046e64f1>] really_probe+0x22f/0xb50
    [<000000005cc35eb7>] driver_probe_device+0x25e/0x370
    [<0000000043c642b2>] bus_for_each_drv+0x11f/0x1b0
    [<000000005e3d09f0>] __device_attach+0x1c6/0x2f0
    [<00000000a72c362f>] bus_probe_device+0x1a6/0x260
    [<0000000008478399>] device_add+0x10a3/0x18e0
    [<00000000cf07b48c>] vmbus_device_register+0xe7/0x1e0 [hv_vmbus]
    [<00000000d46cf032>] vmbus_add_channel_work+0x8ab/0x1770 [hv_vmbus]
    [<000000002c94bb64>] process_one_work+0x919/0x17d0
    [<0000000096de6781>] worker_thread+0x87/0xb40
    [<00000000fbe7397e>] kthread+0x333/0x3f0
    [<000000004f844269>] ret_from_fork+0x3a/0x50

rndis_filter_device_add() allocates an instance of struct rndis_device
which never gets deallocated as rndis_filter_device_remove() sets
net_device->extension which points to the rndis_device struct to NULL,
leaving the rndis_device dangling.

Since net_device->extension is eventually freed in free_netvsc_device(),
we refrain from setting it to NULL inside rndis_filter_device_remove()

Signed-off-by: Mohammed Gamal <mgamal@redhat.com>
---
 drivers/net/hyperv/rndis_filter.c | 2 --
 1 file changed, 2 deletions(-)

> -----Original Message-----
> From: Mohammed Gamal <mgamal@redhat.com>
> Sent: Tuesday, January 14, 2020 8:10 AM
> To: linux-hyperv@vger.kernel.org; Stephen Hemminger
> <sthemmin@microsoft.com>; Haiyang Zhang <haiyangz@microsoft.com>;
> netdev@vger.kernel.org
> Cc: KY Srinivasan <kys@microsoft.com>; sashal@kernel.org; vkuznets
> <vkuznets@redhat.com>; cavery <cavery@redhat.com>; linux-
> kernel@vger.kernel.org; Mohammed Gamal <mgamal@redhat.com>
> Subject: [PATCH v2] hv_netvsc: Fix memory leak when removing rndis device
> 
> kmemleak detects the following memory leak when hot removing a network
> device:
> 
> unreferenced object 0xffff888083f63600 (size 256):
>   comm "kworker/0:1", pid 12, jiffies 4294831717 (age 1113.676s)
>   hex dump (first 32 bytes):
>     00 40 c7 33 80 88 ff ff 00 00 00 00 10 00 00 00  .@.3............
>     00 00 00 00 ad 4e ad de ff ff ff ff 00 00 00 00  .....N..........
>   backtrace:
>     [<00000000d4a8f5be>] rndis_filter_device_add+0x117/0x11c0 [hv_netvsc]
>     [<000000009c02d75b>] netvsc_probe+0x5e7/0xbf0 [hv_netvsc]
>     [<00000000ddafce23>] vmbus_probe+0x74/0x170 [hv_vmbus]
>     [<00000000046e64f1>] really_probe+0x22f/0xb50
>     [<000000005cc35eb7>] driver_probe_device+0x25e/0x370
>     [<0000000043c642b2>] bus_for_each_drv+0x11f/0x1b0
>     [<000000005e3d09f0>] __device_attach+0x1c6/0x2f0
>     [<00000000a72c362f>] bus_probe_device+0x1a6/0x260
>     [<0000000008478399>] device_add+0x10a3/0x18e0
>     [<00000000cf07b48c>] vmbus_device_register+0xe7/0x1e0 [hv_vmbus]
>     [<00000000d46cf032>] vmbus_add_channel_work+0x8ab/0x1770 [hv_vmbus]
>     [<000000002c94bb64>] process_one_work+0x919/0x17d0
>     [<0000000096de6781>] worker_thread+0x87/0xb40
>     [<00000000fbe7397e>] kthread+0x333/0x3f0
>     [<000000004f844269>] ret_from_fork+0x3a/0x50
> 
> rndis_filter_device_add() allocates an instance of struct rndis_device which
> never gets deallocated as rndis_filter_device_remove() sets net_device-
> >extension which points to the rndis_device struct to NULL, leaving the
> rndis_device dangling.
> 
> Since net_device->extension is eventually freed in free_netvsc_device(), we
> refrain from setting it to NULL inside rndis_filter_device_remove()
> 
> Signed-off-by: Mohammed Gamal <mgamal@redhat.com>
> ---
>  drivers/net/hyperv/rndis_filter.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/net/hyperv/rndis_filter.c b/drivers/net/hyperv/rndis_filter.c
> index 857c4bea451c..e66d77dc28c8 100644
> --- a/drivers/net/hyperv/rndis_filter.c
> +++ b/drivers/net/hyperv/rndis_filter.c
> @@ -1443,8 +1443,6 @@ void rndis_filter_device_remove(struct hv_device
> *dev,
>  	/* Halt and release the rndis device */
>  	rndis_filter_halt_device(net_dev, rndis_dev);
> 
> -	net_dev->extension = NULL;
> -
>  	netvsc_device_remove(dev);

Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>

From: Mohammed Gamal <mgamal@redhat.com>
Date: Tue, 14 Jan 2020 15:09:50 +0200

> kmemleak detects the following memory leak when hot removing
> a network device:
> 
> unreferenced object 0xffff888083f63600 (size 256):
 ...
> 
> rndis_filter_device_add() allocates an instance of struct rndis_device
> which never gets deallocated as rndis_filter_device_remove() sets
> net_device->extension which points to the rndis_device struct to NULL,
> leaving the rndis_device dangling.
> 
> Since net_device->extension is eventually freed in free_netvsc_device(),
> we refrain from setting it to NULL inside rndis_filter_device_remove()
> 
> Signed-off-by: Mohammed Gamal <mgamal@redhat.com>

Applied, thanks.