linux-kernel - Re: [PATCH] PCI/hotplug: fix potential null pointer deference

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Message-ID: <20190802001451.GH151852@google.com>
Date:   Thu, 1 Aug 2019 19:14:51 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Young Xiao <92siuyang@...il.com>,
        Tyrel Datwyler <tyreld@...ux.vnet.ibm.com>,
        linux-pci@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PCI/hotplug: fix potential null pointer deference

On Fri, Jun 14, 2019 at 04:56:32PM +0300, Andy Shevchenko wrote:
> On Fri, Jun 14, 2019 at 3:40 PM Young Xiao <92siuyang@...il.com> wrote:
> >
> > There is otherwise a risk of a null pointer dereference.
> 
> Had you analyze the code?
> How come that prevnode can become NULL?

Dropping this for now.  Young, if there's a scenario where prevnode
can actually be NULL, please mention that in the changelog and repost
this.

> > Signed-off-by: Young Xiao <92siuyang@...il.com>
> > ---
> >  drivers/pci/hotplug/cpqphp_ctrl.c | 10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/pci/hotplug/cpqphp_ctrl.c b/drivers/pci/hotplug/cpqphp_ctrl.c
> > index b7f4e1f..3c8399f 100644
> > --- a/drivers/pci/hotplug/cpqphp_ctrl.c
> > +++ b/drivers/pci/hotplug/cpqphp_ctrl.c
> > @@ -598,10 +598,11 @@ static struct pci_resource *get_io_resource(struct pci_resource **head, u32 size
> >                         *head = node->next;
> >                 } else {
> >                         prevnode = *head;
> > -                       while (prevnode->next != node)
> > +                       while (prevnode && prevnode->next != node)
> >                                 prevnode = prevnode->next;
> >
> > -                       prevnode->next = node->next;
> > +                       if (prevnode)
> > +                               prevnode->next = node->next;
> >                 }
> >                 node->next = NULL;
> >                 break;
> > @@ -788,10 +789,11 @@ static struct pci_resource *get_resource(struct pci_resource **head, u32 size)
> >                         *head = node->next;
> >                 } else {
> >                         prevnode = *head;
> > -                       while (prevnode->next != node)
> > +                       while (prevnode && prevnode->next != node)
> >                                 prevnode = prevnode->next;
> >
> > -                       prevnode->next = node->next;
> > +                       if (prevnode)
> > +                               prevnode->next = node->next;
> >                 }
> >                 node->next = NULL;
> >                 break;
> > --
> > 2.7.4
> >
> 
> 
> -- 
> With Best Regards,
> Andy Shevchenko