Date:   Thu, 16 Mar 2023 14:22:35 -0400
From:   Alan Stern <stern@rowland.harvard.edu>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Valery Zabrovsky <valthebrewer@yandex.ru>,
        Guo Zhengkui <guozhengkui@vivo.com>,
        Aaro Koskinen <aaro.koskinen@iki.fi>,
        Mian Yousaf Kaukab <yousaf.kaukab@intel.com>,
        Felipe Balbi <balbi@ti.com>,
        Alexey Khoroshilov <khoroshilov@ispras.ru>,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        lvc-project@linuxtesting.org
Subject: Re: [PATCH] usb: gadget: net2280: fix NULL pointer dereference
Message-ID: <2be27aee-1a2d-4c5c-bb62-018e1340d2ad@rowland.harvard.edu>
References: <20230316155356.13391-1-valthebrewer@yandex.ru>
 <ZBNBlwc9lt+pLFkd@kroah.com>
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On Thu, Mar 16, 2023 at 05:19:35PM +0100, Greg Kroah-Hartman wrote:
> On Thu, Mar 16, 2023 at 06:53:55PM +0300, Valery Zabrovsky wrote:
> > In net2280_free_request():
> > If _ep is NULL, then ep is NULL and is dereferenced
> > while trying to produce an error message.
> 
> How can that ever happen?  How did you test and hit this?
> 
> > The patch replaces dev_err() with pr_err() which works fine.
> 
> That's not a good idea for driver code to use, sorry.
> 
> > Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> As I have said before, your testing framework needs a lot more work.
> 
> good luck!

In situations like this, it might be better to remove the check 
entirely.  If a driver does pass a NULL pointer, it will lead to an 
invalid pointer dereference which will certainly cause an oops and might 
very well crash the system.  That would be a lot more noticeable than an 
error message hidden in a kernel log!

Greg, is there any general policy about the need for sanity checks such 
as this one?  Like, don't put them in whenever a failure would lead 
to an immediate fault which would be easy to track down?

Alan Stern