Re: Fw: Oops in hidinput_hid_event

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On Tue, 19 Jul 2005 09:30:58 -0400 Vojtech Pavlik wrote:

> On Mon, Jul 18, 2005 at 02:16:37PM -0700, Pete Zaitcev wrote:
> 
> > I think this patch is rather obvious, so maybe I should ask Andrew to
> > apply it to -mm for now, to get some testing. Would that help to verify
> > it for acceptance?
> 
> Your patch is perfectly OK, my NULL check was indeed completely wrong.
> 
> I need to find out how there can be an input event happening without its
> associated input structure, though, since the oops actually reveals a
> deeper problem.

hidinput_connect() does:

	for (k = HID_INPUT_REPORT; k <= HID_OUTPUT_REPORT; k++)
		... loop which calls hidinput_configure_usage(),
		    which initializes report->hidinput pointers ...

So ->hidinput is getting set only for fields of input and output
reports, but the device may also support feature reports, and for their
fields ->hidinput will remain NULL.  When such report is requested with
hid_submit_report(hid, report, USB_DIR_IN), the completed urb will be
handled by hid_ctrl(), which will call hid_input_report() for it; this
corresponds to the traceback in oops.

BTW, the driver requests all feature reports during initialization (in
hid_init_reports()), but it does not oops there, because
hidinput_connect() is called only later, and therefore HID_CLAIMED_INPUT
is not yet set.

However, I still don't understand where hid_submit_report() gets called
for a feature report in the reported case (hidinput_input_event() can
submit only output reports, and a call from hiddev is unlikely to be
triggered by a NumLock press).

> So that's why I didn't apply the patch yet.
> 
> > Begin forwarded message:
> > 
> > Date: Tue, 28 Jun 2005 15:00:23 -0700
> > From: Pete Zaitcev <[email protected]>
> > To: [email protected]
> > Cc: [email protected], [email protected]
> > Subject: Oops in hidinput_hid_event
> > 
> > Hi, Vojtech:
> > 
> > Someone reported a bug in Fedora, which runs a largely unmodified upstream
> > kernel in this area. Whenever the user hits a key which switches LED,
> > the system oopses. Here's a trace:
> > 
> > Unable to handle kernel NULL pointer dereference at virtual address 000000c8
> > EFLAGS: 00010006   (2.6.11-1.1369_FC4smp)
> > EIP is at hidinput_hid_event+0x2d/0x292                                       
> > Call Trace:           
> >  [<c02872e0>] hid_process_event+0x57/0x5f
> >  [<c028758a>] hid_input_field+0x2a2/0x2ac
> >  [<c0287632>] hid_input_report+0x9e/0xb8
> >  [<c0287f62>] hid_ctrl+0x14c/0x151
> >  [<e0a21060>] uhci_destroy_urb_priv+0xb5/0x10a [uhci_hcd]
> >  [<c027dab5>] usb_hcd_giveback_urb+0x24/0x67
> >  [<e0a22360>] uhci_finish_urb+0x2d/0x38 [uhci_hcd]
> >  [<e0a223af>] uhci_finish_completion+0x44/0x56 [uhci_hcd]
> >  [<e0a224a2>] uhci_scan_schedule+0xaa/0x13a [uhci_hcd]
> >  [<c023413d>] i8042_interrupt+0x121/0x234
> >  [<e0a226d0>] uhci_irq+0x47/0x10d [uhci_hcd]
> > 
> > Full trace at
> >  https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=160709
> > 
> > Any ideas?
> > 
> > By the way, it seems that I see a bug in hidinput_hid_event.
> > The check for NULL can never work, becaue &hidinput->input
> > is nonzero at all times. How about this?
> > 
> > --- linux-2.6.12/drivers/usb/input/hid-input.c	2005-06-21 12:58:47.000000000 -0700
> > +++ linux-2.6.12-lem/drivers/usb/input/hid-input.c	2005-06-28 14:57:22.000000000 -0700
> > @@ -397,11 +397,12 @@
> >  
> >  void hidinput_hid_event(struct hid_device *hid, struct hid_field *field, struct hid_usage *usage, __s32 value, struct pt_regs *regs)
> >  {
> > -	struct input_dev *input = &field->hidinput->input;
> > +	struct input_dev *input;
> >  	int *quirks = &hid->quirks;
> >  
> > -	if (!input)
> > +	if (!field->hidinput)
> >  		return;
> > +	input = &field->hidinput->input;
> >  
> >  	input_regs(input, regs);
> >  
> > 
> > -- Pete
> > 
> 
> -- 
> Vojtech Pavlik
> SuSE Labs, SuSE CR

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