Re: [PATCH] x86/PCI: Fix Null pointer dereference after call to pcie_find_root_port()

[Mario Limonciello <mario.limonciello@amd.com>]

On 8/12/2024 15:51, Bjorn Helgaas wrote:
> [+cc Mario, 7d08f21f8c63 author]
> 
> On Mon, Aug 12, 2024 at 01:26:59PM -0700, Samasth Norway Ananda wrote:
>> If pcie_find_root_port() is unable to locate a root port, it will return
>> NULL. This NULL pointer needs to be handled before trying to dereference.
>>
>> Fixes: 7d08f21f8c63 ("x86/PCI: Avoid PME from D3hot/D3cold for AMD Rembrandt and Phoenix USB4")
>> Signed-off-by: Samasth Norway Ananda <samasth.norway.ananda@oracle.com>
>> ---
>>   arch/x86/pci/fixup.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/pci/fixup.c b/arch/x86/pci/fixup.c
>> index b33afb240601..98a9bb92d75c 100644
>> --- a/arch/x86/pci/fixup.c
>> +++ b/arch/x86/pci/fixup.c
>> @@ -980,7 +980,7 @@ static void amd_rp_pme_suspend(struct pci_dev *dev)
>>   		return;
>>   
>>   	rp = pcie_find_root_port(dev);
>> -	if (!rp->pm_cap)
>> +	if (!rp || !rp->pm_cap)
> 
> Seems reasonable.  I suspect we haven't seen problems because these
> quirks are limited to Device IDs that are all PCIe, but I think we
> should check on principle and because it may be copied elsewhere where
> it *does* matter.

Yeah totally agree, if nothing else it prevents copy/paste mistakes.

HOWEVER I don't think this needs to be a "Fixes" tag because there is no 
problem in THIS code on the applicable systems.  Those PCI devices are 
always attached to a root port.  So Bjorn I would suggest stripping the 
Fixes tag when committing.

Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>

> 
>>   		return;
>>   
>>   	rp->pme_support &= ~((PCI_PM_CAP_PME_D3hot|PCI_PM_CAP_PME_D3cold) >>
>> @@ -994,7 +994,7 @@ static void amd_rp_pme_resume(struct pci_dev *dev)
>>   	u16 pmc;
>>   
>>   	rp = pcie_find_root_port(dev);
>> -	if (!rp->pm_cap)
>> +	if (!rp || !rp->pm_cap)
>>   		return;
>>   
>>   	pci_read_config_word(rp, rp->pm_cap + PCI_PM_PMC, &pmc);
>> -- 
>> 2.45.2
>>