netdev - Re: [PATCH] hv_netvsc: Fix memory leak when removing rndis device

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Date:   Mon, 13 Jan 2020 12:02:54 -0800
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Mohammed Gamal <mgamal@...hat.com>
Cc:     linux-hyperv@...r.kernel.org, sthemmin@...rosoft.com,
        haiyangz@...rosoft.com, netdev@...r.kernel.org, kys@...rosoft.com,
        sashal@...nel.org, vkuznets@...hat.com, cavery@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hv_netvsc: Fix memory leak when removing rndis device

On Mon, 13 Jan 2020 21:27:52 +0200
Mohammed Gamal <mgamal@...hat.com> wrote:

> 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  .@..............
>     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 and rndis_filter_device_remove() sets
> net_device->extension which points to the rndis_device struct to NULL
> without ever freeing the structure first, leaving it dangling.
> 
> This patch fixes this by freeing the structure before setting
> net_device->extension to NULL
> 
> Signed-off-by: Mohammed Gamal <mgamal@...hat.com>
> ---
>  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 857c4bea451c..d2e094f521a4 100644
> --- a/drivers/net/hyperv/rndis_filter.c
> +++ b/drivers/net/hyperv/rndis_filter.c
> @@ -1443,6 +1443,7 @@ void rndis_filter_device_remove(struct hv_device *dev,
>  	/* Halt and release the rndis device */
>  	rndis_filter_halt_device(net_dev, rndis_dev);
>  
> +	kfree(rndis_dev);
>  	net_dev->extension = NULL;
>  
>  	netvsc_device_remove(dev);

That is one way, but maybe safer to just remove the line that sets
extension to NULL. That way netvsc_device_remove will clean it up:
    netvsc_device_remove -> free_netvsc_device_rcu -> free_netvsc_device.