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

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Date:   Mon, 10 May 2021 15:32:17 -0700
From:   Tong Zhang <ztong0001@...il.com>
To:     Hans Verkuil <hverkuil-cisco@...all.nl>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] media: cobalt: fix null-ptr-deref when there is no PCI bridge

On Wed, May 5, 2021 at 2:18 AM Hans Verkuil <hverkuil-cisco@...all.nl> wrote:
>
> On 24/04/2021 02:52, Tong Zhang wrote:
> > the PCI bridge might be NULL, so we'd better check before use it
> >
> > [    1.870569] RIP: 0010:pcie_bus_link_get_lanes.isra.0+0x26/0x59 [cobalt]
> > [    1.875880] Call Trace:
> > [    1.876013]  cobalt_probe.cold+0x1be/0xc11 [cobalt]
> > [    1.876683]  pci_device_probe+0x10f/0x1c0
>
> How did you test this? With some virtualized PCI bus or something? I'm not sure
> how this can happen.
>
Hello Hans,
IMHO bus->self is pci bridge device and we can have a system
configuration that does not have such a bridge,
in this case, bus->self is NULL.
- Tong
> Regards,
>
>         Hans
>
> >
> > Signed-off-by: Tong Zhang <ztong0001@...il.com>
> > ---
> >  drivers/media/pci/cobalt/cobalt-driver.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/media/pci/cobalt/cobalt-driver.c b/drivers/media/pci/cobalt/cobalt-driver.c
> > index 0695078ef812..5687ed4869ac 100644
> > --- a/drivers/media/pci/cobalt/cobalt-driver.c
> > +++ b/drivers/media/pci/cobalt/cobalt-driver.c
> > @@ -189,6 +189,8 @@ void cobalt_pcie_status_show(struct cobalt *cobalt)
> >       u32 capa;
> >       u16 stat, ctrl;
> >
> > +     if (!pci_bus_dev)
> > +             return;
> >       if (!pci_is_pcie(pci_dev) || !pci_is_pcie(pci_bus_dev))
> >               return;
> >
> > @@ -247,6 +249,8 @@ static unsigned pcie_bus_link_get_lanes(struct cobalt *cobalt)
> >       struct pci_dev *pci_dev = cobalt->pci_dev->bus->self;
> >       u32 link;
> >
> > +     if (!pci_dev)
> > +             return 0;
> >       if (!pci_is_pcie(pci_dev))
> >               return 0;
> >       pcie_capability_read_dword(pci_dev, PCI_EXP_LNKCAP, &link);
> >
>