linux-kernel - Re: [PATCH 2/2] MIPS/PCI: Fix pcibios_scan

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Message-ID: <20170710145553.GA20365@bhelgaas-glaptop.roam.corp.google.com>
Date:   Mon, 10 Jul 2017 09:55:53 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...tec.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH 2/2] MIPS/PCI: Fix pcibios_scan_bus() NULL check code path

On Mon, Jul 10, 2017 at 01:34:09PM +0100, Lorenzo Pieralisi wrote:
> If pci_scan_root_bus() fails (ie returns NULL) pcibios_scan_bus() must
> return immediately since the struct pci_bus pointer it returns is not
> valid and cannot be used.
> 
> Move code checking the pci_scan_root_bus() return value to reinstate
> proper pcibios_scanbus() error path behaviour.
> 
> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> Cc: Ralf Baechle <ralf@...ux-mips.org>
> Cc: Paul Burton <paul.burton@...tec.com>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>

I agree this is certainly broken.  In fact, I think I broke it with
9e808eb6a768 ("PCI: Cleanup control flow") in 2015.  So probably v4.14
material?

> ---
>  arch/mips/pci/pci-legacy.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/mips/pci/pci-legacy.c b/arch/mips/pci/pci-legacy.c
> index 174575a..71d62f8 100644
> --- a/arch/mips/pci/pci-legacy.c
> +++ b/arch/mips/pci/pci-legacy.c
> @@ -89,16 +89,16 @@ static void pcibios_scanbus(struct pci_controller *hose)
>  	pci_add_resource(&resources, hose->busn_resource);
>  	bus = pci_scan_root_bus(NULL, next_busno, hose->pci_ops, hose,
>  				&resources);
> -	hose->bus = bus;
> -
> -	need_domain_info = need_domain_info || pci_domain_nr(bus);
> -	set_pci_need_domain_info(hose, need_domain_info);
> -
>  	if (!bus) {
>  		pci_free_resource_list(&resources);
>  		return;
>  	}
>  
> +	hose->bus = bus;
> +
> +	need_domain_info = need_domain_info || pci_domain_nr(bus);
> +	set_pci_need_domain_info(hose, need_domain_info);
> +
>  	next_busno = bus->busn_res.end + 1;
>  	/* Don't allow 8-bit bus number overflow inside the hose -
>  	   reserve some space for bridges. */
> -- 
> 2.10.0
>