linux-kernel - Re: [PATCH] network: wireless: p54u: Fix race between disconnect and firmware loading

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Date:   Tue, 28 May 2019 10:17:19 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Kalle Valo <kvalo@...eaurora.org>
cc:     Christian Lamparter <chunkeey@...il.com>,
        syzbot <syzbot+200d4bb11b23d929335f@...kaller.appspotmail.com>,
        <davem@...emloft.net>, <andreyknvl@...gle.com>,
        <syzkaller-bugs@...glegroups.com>,
        Kernel development list <linux-kernel@...r.kernel.org>,
        USB list <linux-usb@...r.kernel.org>,
        <linux-wireless@...r.kernel.org>, <netdev@...r.kernel.org>
Subject: Re: [PATCH] network: wireless: p54u: Fix race between disconnect
 and firmware loading

On Tue, 28 May 2019, Kalle Valo wrote:

> The correct prefix is "p54:", but I can fix that during commit.

Oh, okay, thanks.

> > Index: usb-devel/drivers/net/wireless/intersil/p54/p54usb.c
> > ===================================================================
> > --- usb-devel.orig/drivers/net/wireless/intersil/p54/p54usb.c
> > +++ usb-devel/drivers/net/wireless/intersil/p54/p54usb.c
> > @@ -33,6 +33,8 @@ MODULE_ALIAS("prism54usb");
> >  MODULE_FIRMWARE("isl3886usb");
> >  MODULE_FIRMWARE("isl3887usb");
> >  
> > +static struct usb_driver p54u_driver;
> 
> How is it safe to use static variables from a wireless driver? For
> example, what if there are two p54 usb devices on the host? How do we
> avoid a race in that case?

There is no race.  This structure is not per-device; it refers only to
the driver.  In fact, the line above is only a forward declaration --
the actual definition of p54u_driver was already in the source file.

Alan Stern