linux-kernel - Re: [syzbot] general protection fault in __device

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Date:   Fri, 3 Jun 2022 17:52:38 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        syzbot <syzbot+dd3c97de244683533381@...kaller.appspotmail.com>,
        hdanton@...a.com, lenb@...nel.org, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org, rafael.j.wysocki@...el.com,
        rafael@...nel.org, rjw@...ysocki.net,
        syzkaller-bugs@...glegroups.com, linux-usb@...r.kernel.org
Subject: Re: [syzbot] general protection fault in __device_attach

On Fri, Jun 03, 2022 at 11:42:19AM -0400, Alan Stern wrote:
> On Fri, Jun 03, 2022 at 02:04:04PM +0300, Andy Shevchenko wrote:
> > On Fri, Jun 03, 2022 at 03:02:07AM -0700, syzbot wrote:
> > > syzbot has bisected this issue to:
> > > 
> > > commit a9c4cf299f5f79d5016c8a9646fa1fc49381a8c1
> > > Author: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > > Date:   Fri Jun 18 13:41:27 2021 +0000
> > > 
> > >     ACPI: sysfs: Use __ATTR_RO() and __ATTR_RW() macros
> > 
> > Hmm... It's not obvious at all how this change can alter the behaviour so
> > drastically. device_add() is called from USB core with intf->dev.name == NULL
> > by some reason. A-ha, seems like fault injector, which looks like
> > 
> > 	dev_set_name(&intf->dev, "%d-%s:%d.%d", dev->bus->busnum,
> > 		     dev->devpath, configuration, ifnum);
> > 
> > missed the return code check.
> > 
> > But I'm not familiar with that code at all, adding Linux USB ML and Alan.
> 
> I can't see any connection between this bug and acpi/sysfs.c.  Is it a 
> bad bisection?
> 
> It looks like you're right about dev_set_name() failing.  In fact, the 
> kernel appears to be littered with calls to that routine which do not 
> check the return code (the entire subtree below drivers/usb/ contains 
> only _one_ call that does check the return code!).  The function doesn't 
> have any __must_check annotation, and its kerneldoc doesn't mention the 
> return code or the possibility of a failure.
> 
> Apparently the assumption is that if dev_set_name() fails then 
> device_add() later on will also fail, and the problem will be detected 
> then.
> 
> So now what should happen when device_add() for an interface fails in 
> usb_set_configuration()?

But how can that really fail on a real system?

Is this just due to error-injection stuff?  If so, I'm really loath to
rework the world for something that can never happen in real life.

Or is this a real syzbot-found-with-reproducer issue?

thanks,

greg k-h