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 09:03:34 +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 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
> > >
> > > [    1.246492] BUG: kernel NULL pointer dereference, address: 00000000000000c0
> > > [    1.248731] RIP: 0010:pci_read_config_byte+0x5/0x40
> > > [    1.253998] Call Trace:
> > > [    1.254131]  ? alcor_pci_find_cap_offset.isra.0+0x3a/0x100 [alcor_pci]
> > > [    1.254476]  alcor_pci_probe+0x169/0x2d5 [alcor_pci]
> > >
> > > Signed-off-by: Tong Zhang <ztong0001@...il.com>
> > > ---
> > >  drivers/misc/cardreader/alcor_pci.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > >
> > > diff --git a/drivers/misc/cardreader/alcor_pci.c b/drivers/misc/cardreader/alcor_pci.c
> > > index cd402c89189e..1c33453fd5c7 100644
> > > --- a/drivers/misc/cardreader/alcor_pci.c
> > > +++ b/drivers/misc/cardreader/alcor_pci.c
> > > @@ -102,6 +102,9 @@ static int alcor_pci_find_cap_offset(struct alcor_pci_priv *priv,
> > >       u8 val8;
> > >       u32 val32;
> > >
> > > +     if (!pci)
> > > +             return 0;
> > > +
> > >       where = ALCOR_CAP_START_OFFSET;
> > >       pci_read_config_byte(pci, where, &val8);
> > >       if (!val8)
> > > --
> > > 2.25.1
> > >
> >
> > 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?

Did you see this on a real system?  How did you duplicate the error
listed here?

thanks,

greg k-h