linux-kernel - Re: Is usb_hcd_giveback_urb() allowed in task context?

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Message-ID: <20201005151857.GA2309511@kroah.com>
Date:   Mon, 5 Oct 2020 17:18:57 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Valentina Manea <valentina.manea.m@...il.com>,
        Shuah Khan <shuah@...nel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        USB list <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Nazime Hande Harputluoglu <handeharputlu@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: Is usb_hcd_giveback_urb() allowed in task context?

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 :)

thanks,

greg k-h