Subject: Re: [PATCH] net: usbnet: fix a memory leak bug

From: Jack Pham <[email-masked]>
Date: Wed, 14 Aug 2019 14:32:03 -0700

On Wed, Aug 14, 2019 at 12:41:33PM -0500, Wenwen Wang wrote:
> In usbnet_start_xmit(), 'urb->sg' is allocated through kmalloc_array() by
> invoking build_dma_sg(). Later on, if 'CONFIG_PM' is defined and the if
> branch is taken, the execution will go to the label 'deferred'. However,
> 'urb->sg' is not deallocated on this execution path, leading to a memory
> leak bug.
> 
> Signed-off-by: Wenwen Wang <[email-masked]>
> ---
>  drivers/net/usb/usbnet.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
> index 72514c4..f17fafa 100644
> --- a/drivers/net/usb/usbnet.c
> +++ b/drivers/net/usb/usbnet.c
> @@ -1433,6 +1433,7 @@ netdev_tx_t usbnet_start_xmit (struct sk_buff *skb,
>  		usb_anchor_urb(urb, &dev->deferred);
>  		/* no use to process more packets */
>  		netif_stop_queue(net);
> +		kfree(urb->sg);
>  		usb_put_urb(urb);

The URB itself is not getting freed here; it is merely added to the
anchor list and will be submitted later upon usbnet_resume(). Therefore
freeing the SG list is premature and incorrect, as it will get freed in
either the tx_complete/tx_done path or upon URB submission failure.

>  		spin_unlock_irqrestore(&dev->txq.lock, flags);
>  		netdev_dbg(dev->net, "Delaying transmission for resumption\n");

Jack
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