Re: [PATCH] usbnet: ipheth: fix potential recvmsg bug and recvmsg bug 2

[David Miller <davem@davemloft.net>]

From: Bernd Eckstein <3erndeckstein@gmail.com>
Date: Fri, 23 Nov 2018 13:51:26 +0100

> The bug is not easily reproducable, as it may occur very infrequently
> (we had machines with 20minutes heavy downloading before it occurred)
> However, on a virual machine (VMWare on Windows 10 host) it occurred
> pretty frequently (1-2 seconds after a speedtest was started)
> 
> dev->tx_skb mab be freed via dev_kfree_skb_irq on a callback
> before it is set.
> 
> This causes the following problems:
> - double free of the skb or potential memory leak
> - in dmesg: 'recvmsg bug' and 'recvmsg bug 2' and eventually
>   general protection fault
> 
> Example dmesg output:
 ...
> The proposed patch eliminates a potential racing condition.
> Before, usb_submit_urb was called and _after_ that, the skb was attached
> (dev->tx_skb). So, on a callback it was possible, however unlikely that the
> skb was freed before it was set. That way (because dev->tx_skb was not set
> to NULL after it was freed), it could happen that a skb from a earlier
> transmission was freed a second time (and the skb we should have freed did
> not get freed at all)
> 
> Now we free the skb directly in ipheth_tx(). It is not passed to the
> callback anymore, eliminating the posibility of a double free of the same
> skb. Depending on the retval of usb_submit_urb() we use dev_kfree_skb_any()
> respectively dev_consume_skb_any() to free the skb.
> 
> Signed-off-by: Oliver Zweigle <Oliver.Zweigle@faro.com>
> Signed-off-by: Bernd Eckstein <3ernd.Eckstein@gmail.com>

Applied and queued up for -stable, thanks.