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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Tue, 25 Sep 2018 17:17:29 +0200
Message-ID: <CAAeHK+weYa=d=dSgCJ0o6dZBAxBakeAy2hodHhuPSeTr3iesuA@mail.gmail.com>
Subject: Re: [PATCH] usb: usbfs: fix crash in check_ctrlrecip()->usb_find_alt_setting()
To:     Alan Stern <stern@rowland.harvard.edu>
Cc:     Vladis Dronov <vdronov@redhat.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Oliver Neukum <oneukum@suse.com>,
        Hans de Goede <hdegoede@redhat.com>,
        syzkaller <syzkaller@googlegroups.com>,
        USB list <linux-usb@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        stable <stable@vger.kernel.org>
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On Tue, Sep 25, 2018 at 5:15 PM, Alan Stern <stern@rowland.harvard.edu> wrote:
> 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.)

What about adding a WARN_ON()? It doesn't crash the kernel and it will
be detected and reported by syzbot.