linux-kernel - Re: [PATCH] misc: alcor_pci: fix null-ptr-deref when there is no PCI bridge

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Date:   Tue, 11 May 2021 19:57:29 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Tong Zhang <ztong0001@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] misc: alcor_pci: fix null-ptr-deref when there is no PCI
 bridge

On Tue, May 11, 2021 at 10:17:12AM -0700, Tong Zhang wrote:
> On Tue, May 11, 2021 at 12:03 AM Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
> >
> > On Mon, May 10, 2021 at 03:20:02PM -0700, Tong Zhang wrote:
> > > On Mon, May 10, 2021 at 7:36 AM Greg Kroah-Hartman
> > > <gregkh@...uxfoundation.org> wrote:
> > > >
> > > > On Mon, Apr 26, 2021 at 06:07:27PM -0400, Tong Zhang wrote:
> > > > > the PCI bridge might be NULL, so we'd better check before use it
> > > >
> > > > I do not understand, how can pci ever be NULL?  There is only 1 way this
> > >
> > > Hi Greg,
> > > I think the problem is with
> > >     priv->parent_pdev = pdev->bus->self
> > > where bus->self can be NULL. when bus->self is NULL, calling
> >
> > How can bus->self be NULL?
> 
> Hi Greg,
> Please correct me if I am wrong,
> when bus->self is not NULL, it means there is a bridge,
> However, a device can be directly attached to the port on the root
> complex. In this case, the bus->self is NULL.

Does that ever happen with a device on the root like that?

> > Did you see this on a real system?  How did you duplicate the error
> > listed here?
> I did this in QEMU. If QEMU is considered not real, then I haven't
> seen an alcor controller configured in this way in a real system.
> That being said, this kind of configuration is still legit IMHO.

Ah, ok, that makes more sense, this is a virtual system.

I suggest, again, steping back up and just not calling this function if
you are on the root, as it does not make any sense to do so for a device
that is not there.

thanks,

greg k-h