linux-kernel - Re: [PATCH v1 1/1] usb: gadget: NCM: NULL pointer dereference in eth_start

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Date:	Mon, 25 Apr 2016 17:51:57 +0100
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	<jim_baxter@...tor.com>
Cc:	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Felipe Balbi <balbi@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mike Looijmans <mike.looijmans@...ic.nl>,
	Robert Baldyga <r.baldyga@...sung.com>,
	Mark Craske <Mark_Craske@...tor.com>
Subject: Re: [PATCH v1 1/1] usb: gadget: NCM: NULL pointer dereference in
 eth_start_xmit

On Mon, 25 Apr 2016 16:25:03 +0100
<jim_baxter@...tor.com> wrote:

> From: Jim Baxter <jim_baxter@...tor.com>
> 
> "Unable to handle kernel NULL pointer dereference at virtual address
> 00000078" is reported with "PC is at eth_start_xmit+0x19c/0x378 [u_ether]"
> 
> The failure scenario is seen when closing the NCM connection while the
> TCP/IPv6 stack is still trying to transmit over NCM.
> 
> Defensive code is missing from commit
> 6d3865f9d41f15ddbcecaa6722871fc0db21d7ab
> "usb: gadget: NCM: Add transmit multi-frame."

This looks inadequate. Surely you also need to hold dev->lock ?

Also it'll also crash at the no zlp test with the same problem.

Alan