Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <CAAeHK+wb4k-LGTjK9F5YbJNviF_+yU+wE_=Vpo9Rn7KFN8vG6Q@mail.gmail.com>
 <20201005151857.GA2309511@kroah.com>
In-Reply-To: <20201005151857.GA2309511@kroah.com>
From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Mon, 5 Oct 2020 17:21:30 +0200
Message-ID: <CAAeHK+zes2Y00+EJ6SVtOHj8YCADw5WSXUEFHWCRgxi=H42+4w@mail.gmail.com>
Subject: Re: Is usb_hcd_giveback_urb() allowed in task context?
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Valentina Manea <valentina.manea.m@gmail.com>,
        Shuah Khan <shuah@kernel.org>,
        Alan Stern <stern@rowland.harvard.edu>,
        USB list <linux-usb@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Dmitry Vyukov <dvyukov@google.com>,
        Nazime Hande Harputluoglu <handeharputlu@google.com>,
        syzkaller <syzkaller@googlegroups.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Mon, Oct 5, 2020 at 5:18 PM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Mon, Oct 05, 2020 at 05:08:11PM +0200, Andrey Konovalov wrote:
> > Dear USB and USB/IP maintainers,
> >
> > While fuzzing the USB/IP stack with syzkaller we've stumbled upon an issue.
> >
> > Currently kcov (the subsystem that is used for coverage collection)
> > USB-related callbacks assume that usb_hcd_giveback_urb() can only be
> > called from interrupt context, as indicated by the comment before the
> > function definition. In the USB/IP code, however, it's called from the
> > task context (see the stack trace below).
> >
> > Is this something that is allowed and we need to fix kcov? Or is this
> > a bug in USB/IP?
>
> It's a bug in kcov, and is not true as you have found out :)

OK, I see, I'll work on a fix, thanks!

Should I also update the comment above usb_hcd_giveback_urb() to
mention that it can be called in_task()? Or is this redundant and is
assumed in general?