linux-kernel - Re: [PATCH] modpost: detect unterminated device id lists

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Date:	Tue, 18 Sep 2007 03:15:14 +0530 (IST)
From:	Satyam Sharma <satyam@...radead.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Satyam Sharma <satyam.sharma@...il.com>,
	Kees Cook <kees@...ntu.com>, Greg KH <greg@...ah.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Jeff Garzik <jeff@...zik.org>, linux-kernel@...r.kernel.org,
	Ben Collins <bcollins@...ntu.com>,
	Michael Wu <flamingice@...rmilk.net>
Subject: Re: [PATCH] modpost: detect unterminated device id lists



On Sun, 16 Sep 2007, Andrew Morton wrote:

> On Mon, 17 Sep 2007 05:54:45 +0530 "Satyam Sharma" <satyam.sharma@...il.com> wrote:
> 
> > On 9/17/07, Andrew Morton <akpm@...ux-foundation.org> wrote:
> > >
> > > I'm getting this:
> > >
> > > rusb2/pvrusb2: struct usb_device_id is 20 bytes.  The last of 3 is:
> > > 0x03 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
> > > 0x00 0x00 0x00 0x00 0x00
> > > FATAL: drivers/media/video/pvrusb2/pvrusb2: struct usb_device_id is not terminated
> > > with a NULL entry!
> > >
> > > ("rusb2/pvrusb2" ??)
> > 
> > Hmm? Are you sure you didn't see any "drivers/media/video/pv" before the
> > "rusb2/pvrusb2" bit?
> 
> Fairly.  I looked twice.

"drivers/media/video/pvrusb2/pvrusb2" comes out correctly here ...


> > Looking at Kees' patch (and the existing code), I've no
> > clue how/why this should happen ... will try to reproduce here ...
> > 
> > 
> > > but:
> > >
> > > struct usb_device_id pvr2_device_table[] = {
> > >         [PVR2_HDW_TYPE_29XXX] = { USB_DEVICE(0x2040, 0x2900) },
> > >         [PVR2_HDW_TYPE_24XXX] = { USB_DEVICE(0x2040, 0x2400) },
> > >         { USB_DEVICE(0, 0) },
> > > };
> > >
> > > looks OK?
> > >
> > > Using plain old "{ }" shut the warning up.
> > 
> > USB_DEVICE(0, 0) is not empty termination, actually, and this looks like
> > a genuine bug caught by the patch. As that dump shows, USB_DEVICE(0, 0)
> > assigns "0x03 0x00" (in little endian) to usb_device_id.match_flags. And
> > I don't think the USB code treats such an entry as an empty entry (?)
> > 
> > Interestingly, the "USB_DEVICE(0, 0)" thing is absent from latest -git
> > tree and also in my copy of 23-rc4-mm1 -- so this looks like something
> > you must've merged recently.
> 
> git-dvb very carefully does
> 
> --- a/drivers/media/video/pvrusb2/pvrusb2-hdw.c~git-dvb
> +++ a/drivers/media/video/pvrusb2/pvrusb2-hdw.c
> @@ -44,7 +44,7 @@
>  struct usb_device_id pvr2_device_table[] = {
>  		[PVR2_HDW_TYPE_29XXX] = { USB_DEVICE(0x2040, 0x2900) },
>  		[PVR2_HDW_TYPE_24XXX] = { USB_DEVICE(0x2040, 0x2400) },
> -       { }
> +       { USB_DEVICE(0, 0) },
> };
> 	 
> MODULE_DEVICE_TABLE(usb, pvr2_device_table);

Ok, this is a false positive indeed, the core USB code does in fact
treat such an entry as an empty entry (usb_match_id() tests only the
.idVendor, .bDeviceClass, .bInterfaceClass and .driver_info members
for non-zero and not the .match_flags member).

However, a quick-grep-and-glance tells us that none of the other 2213
occurrences of USB_DEVICE() in the tree ever do this "(0,0)" thing,
so it does make sense to change this one to a simple "{ }" as well --
that's clearer style anyway, and the "standard" way to empty-terminate
in the rest of the tree, if nothing else.


Satyam
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