linux-kernel - Re: [PATCH] usb: usbfs: fix crash in check_ctrlrecip()->usb_find_alt

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Date:   Tue, 25 Sep 2018 11:15:05 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Vladis Dronov <vdronov@...hat.com>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Oliver Neukum <oneukum@...e.com>,
        Hans de Goede <hdegoede@...hat.com>,
        <syzkaller@...glegroups.com>, <linux-usb@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, stable <stable@...r.kernel.org>
Subject: Re: [PATCH] usb: usbfs: fix crash in check_ctrlrecip()->usb_find_alt_setting()

On Tue, 25 Sep 2018, Vladis Dronov wrote:

> > What reason is there for having two different fixes for the same bug?
> > This one isn't going to get into any mainline trees that don't already
> > have c9a4cb204e9e.
> 
> I believe this is the right thing to do, so usb_find_alt_setting()
> is not called with a known-bad argument.
> 
> Honestly, I would change "if (!config)" in usb_find_alt_setting() to
> "BUG_ON(!config)" so we know when its callers do smth wrong and go

(You'll be lucky if Linus doesn't see that.  He yells at anybody who
suggests adding BUG_ON for anything that doesn't completely crash the
kernel.  The basic problem is that "BUG_ON" is not a good name: That
routine doesn't really report bugs; instead it brings everything to a
halt in situations where the kernel is unable to proceed.  In practice 
this tends to make actual debugging more difficult.)

> fix callers. Unfortunately, I understand this hardly will be accepted.

How is this different from calling kfree() with a NULL argument?

Alan Stern