linux-kernel - Re: [Merge tag 'pci-v4.12-changes' of git] 857f864014: BUG: unable to handle kernel NULL pointer dereference at 00000000000000a8

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Date:   Tue, 13 Jun 2017 21:13:32 +0200 (CEST)
From:   Sven-Haegar Koch <haegar@...net.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
cc:     Logan Gunthorpe <logang@...tatee.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        kernel test robot <fengguang.wu@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKP <lkp@...org>, linux-arm-kernel@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>, wfg@...ux.intel.com,
        Alan Cox <alan@...ux.intel.com>, Arnd Bergmann <arnd@...db.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        David Airlie <airlied@...ux.ie>,
        David Herrmann <dh.herrmann@...il.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>
Subject: Re: [Merge tag 'pci-v4.12-changes' of git] 857f864014: BUG: unable
 to handle kernel NULL pointer dereference at 00000000000000a8

On Tue, 13 Jun 2017, Greg Kroah-Hartman wrote:

> On Tue, Jun 13, 2017 at 10:25:40AM -0600, Logan Gunthorpe wrote:
> > 
> > On 12/06/17 10:35 PM, Greg Kroah-Hartman wrote:
> > > Or better yet, just turn all char major allocations into dynamic, which
> > > would be really good for test systems.  I thought someone proposed
> > > patches for that a long time ago, but I can't find them anymore.  That
> > > would be the simplest solution here.
> > 
> > Would people not complain about that? I would not be surprised if some
> > crazy application is using hard coded major numbers in userspace. So
> > such a change could potentially break userspace...
> 
> For char devices, I doubt it, but we can't take the chance, which is why
> you make it an option.  Then, it's enabled for 'allmodconfig' builds,
> which helps testers out.

At least for /dev/null, /dev/zero, and perhaps /dev/tty it would 
definitely break things if the major+minor number is not static. I have 
multiple chroot environments having only some minimal needed static 
/dev subdir, with naturally no daemons or filesystem creating those 
on-demand. For the main /dev I use whatever the system sets up, so 
devtmpfs with udev.

c'ya
sven-haegar

-- 
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