Re: [Linux-kernel-mentees] [PATCH v2] net: usb: rtl8150: prevent set_ethernet_addr from setting uninit address

From: Greg KH <greg@kroah.com>
To: Anant Thazhemadam <anant.thazhemadam@gmail.com>
Cc: petkan@nucleusys.com,
	syzbot+abbc768b560c84d92fd3@syzkaller.appspotmail.com,
	netdev@vger.kernel.org, linux-usb@vger.kernel.org,
	linux-kernel@vger.kernel.org, kuba@kernel.org,
	linux-kernel-mentees@lists.linuxfoundation.org,
	David Miller <davem@davemloft.net>
Subject: Re: [Linux-kernel-mentees] [PATCH v2] net: usb: rtl8150: prevent set_ethernet_addr from setting uninit address
Date: Fri, 2 Oct 2020 13:54:53 +0200	[thread overview]
Message-ID: <20201002115453.GA3338729@kroah.com> (raw)
In-Reply-To: <83804e93-8f59-4d35-ec61-e9b5e6f00323@gmail.com>

On Fri, Oct 02, 2020 at 05:04:13PM +0530, Anant Thazhemadam wrote:
> 
> On 02/10/20 7:45 am, David Miller wrote:
> > From: Anant Thazhemadam <anant.thazhemadam@gmail.com>
> > Date: Thu,  1 Oct 2020 13:02:20 +0530
> >
> >> When get_registers() fails (which happens when usb_control_msg() fails)
> >> in set_ethernet_addr(), the uninitialized value of node_id gets copied
> >> as the address.
> >>
> >> Checking for the return values appropriately, and handling the case
> >> wherein set_ethernet_addr() fails like this, helps in avoiding the
> >> mac address being incorrectly set in this manner.
> >>
> >> Reported-by: syzbot+abbc768b560c84d92fd3@syzkaller.appspotmail.com
> >> Tested-by: syzbot+abbc768b560c84d92fd3@syzkaller.appspotmail.com
> >> Signed-off-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>
> >> Acked-by: Petko Manolov <petkan@nucleusys.com>
> > First, please remove "Linux-kernel-mentees" from the Subject line.
> >
> > All patch submitters should have their work judged equally, whoever
> > they are.  So this Subject text gives no extra information, and it
> > simply makes scanning Subject lines in one's mailer more difficult.
> I will keep that in mind for all future submissions. Thank you.
> 
> > Second, when a MAC address fails to probe a random MAC address should
> > be selected.  We have helpers for this.  This way an interface still
> > comes up and is usable, even in the event of a failed MAC address
> > probe.
> 
> Okay... I see.
> But this patch is about ensuring that an uninitialized variable's
> value (whatever that may be) is not set as the ethernet address
> blindly (without any form of checking if get_registers() worked
> as expected, or not). And I didn't think uninitialized values being
> set as MAC address was considered a good outcome (after all, it
> seemed to have triggered a bug), especially when it could have
> been avoided by introducing a simple check that doesn't break
> anything.

If the read from the device for the MAC address fails, don't abort the
whole probe process and make the device not work at all, call the
networking core to assign a random MAC address.

> However, if I was mistaken, and if that is something that we can live
> with after all, then I don't really see the understand the purpose of
> similar checks being made (in all the many places that the return
> value of get_registers() (or a similar function gets checked) in the first
> place at all.

Different values and registers determine what should be done with an
error.  It's all relative.

For this type of error, we should gracefully recover and keep on going.
For others, maybe we just ignore the issue, or log it, or something
else, it all depends.

hope this helps,

greg k-h
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