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

[Bjorn Helgaas <helgaas@kernel.org>]

[+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.

>  		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
>