linux-kernel - Re: [Linux-uvc-devel] [BUG] NULL pointer dereference caused by uvcvideo stress test

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <200810152319.17925.laurent.pinchart@skynet.be>
Date:	Wed, 15 Oct 2008 23:19:17 +0200
From:	Laurent Pinchart <laurent.pinchart@...net.be>
To:	Alan Jenkins <alan-jenkins@...fmail.co.uk>
Cc:	linux-uvc-devel@...ts.berlios.de,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Mauro Carvalho Chehab <mchehab@...radead.org>
Subject: Re: [Linux-uvc-devel] [BUG] NULL pointer dereference caused by uvcvideo stress test

Hi Alan,

On Wednesday 15 October 2008, Alan Jenkins wrote:
> Laurent Pinchart wrote:
> > On Wednesday 15 October 2008, Alan Jenkins wrote:
> > > If you look at the trace, it happens as "hald-probe-video" opens the
> > > video device.  This is from Ubuntu 8.04.  Possibly it's significant that
> > > I use the camera first, to make sure it works (I use Kopete, the
> > > settings dialogue includes a video test).
> >
> > The NULL pointer (or rather 0x00000030 pointer) dereference happens in
> > video_open:
> >
> >         file->f_op = fops_get(vfl->fops);
> >         if (file->f_op->open)
> >                 err = file->f_op->open(inode, file);
> >
> > file->f_op ends up being NULL. Either vfl->fops is NULL to begin with, or
> > fops_get failed to get a reference to the file_operations structure.
> >
> > I'd be surprised if vfl->fops was NULL. To rule out that case, can you
> > add a BUG_ON(vfl->fops == NULL) before the call to fops_get ?
> >
> > I'm not too familiar with the module loader, but a quick look at the code
> > shows that the module could be marked as being unloaded
> > (MODULE_STATE_GOING) before its exit function is called. If this is the
> > case video_open would still be called, as the video device would still be
> > registered, but fops_get would fail in try_module_get and return a NULL
> > pointer. It seems the pointer returned by fops_get should be tested in
> > video_open.
> >
> > I've CC'ed the v4l maintainer to get his opinion on this.
>
> I put one before and one after
>
> 134    BUG_ON(vfl->fops == NULL);
> 135    file->f_op = fops_get(vfl->fops);
> 136    BUG_ON(file->f_op == NULL);
>
> and the second one triggered

This confirms my suspicion. Could you please try the attached patch ?

Best regards,

Laurent Pinchart

View attachment "fops_get_check.patch" of type "text/x-diff" (711 bytes)