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Subject: Re: [PATCH] media: cobalt: fix null-ptr-deref when there is no PCI
 bridge
To:     Tong Zhang <ztong0001@gmail.com>
Cc:     Mauro Carvalho Chehab <mchehab@kernel.org>,
        linux-media@vger.kernel.org,
        open list <linux-kernel@vger.kernel.org>
References: <20210424005206.261622-1-ztong0001@gmail.com>
 <b84e0b87-4753-0513-9803-0cda4ceb4adc@xs4all.nl>
 <CAA5qM4BtejMqUa+eJLV+9q26E3Du-MiTasB=knCh+Qsw3HjApg@mail.gmail.com>
From:   Hans Verkuil <hverkuil-cisco@xs4all.nl>
Message-ID: <a6052f9f-5d2e-e713-1ab4-27d38d14fa99@xs4all.nl>
Date:   Wed, 26 May 2021 15:07:06 +0200
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On 11/05/2021 00:32, Tong Zhang wrote:
> On Wed, May 5, 2021 at 2:18 AM Hans Verkuil <hverkuil-cisco@xs4all.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.

That does not answer my question :-)

You show a backtrace in the commit message, how did you get that?

Regards,

	Hans

> - Tong
>> Regards,
>>
>>         Hans
>>
>>>
>>> Signed-off-by: Tong Zhang <ztong0001@gmail.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);
>>>
>>