linux-kernel - Re: [PATCH v1 1/1] PCI: Avoid potential out-of-bounds read in pci_dev_for_each

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Date:   Fri, 3 Nov 2023 13:46:14 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jonas Gorski <jonas.gorski@...il.com>
Subject: Re: [PATCH v1 1/1] PCI: Avoid potential out-of-bounds read in
 pci_dev_for_each_resource()

On Mon, Oct 30, 2023 at 01:42:18PM +0200, Andy Shevchenko wrote:
> Coverity complains that pointer in the pci_dev_for_each_resource()
> may be wrong, i.e. mighe be used for the out-of-bounds read.
> 
> There is no actual issue right now, because we have another check
> afterwards and the out-of-bounds read is not being performed. In any
> case it's better code with this get fixed, hence the proposed change.
> 
> As Jonas pointed out "It probably makes the code slightly less
> performant as res will now be checked for being not NULL (which will
> always be true), but I doubt it will be significant (or in any hot
> paths)."
> 
> Fixes: 09cc90063240 ("PCI: Introduce pci_dev_for_each_resource()")
> Reported-by: Bjorn Helgaas <helgaas@...nel.org>
> Closes: https://lore.kernel.org/r/20230509182122.GA1259567@bhelgaas
> Suggested-by: Jonas Gorski <jonas.gorski@...il.com>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

Thanks, Andy, I'll look at this soon after v6.7-rc1 (probably Nov 12).

> ---
>  include/linux/pci.h | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 60ca768bc867..19adad23a204 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -2127,14 +2127,14 @@ int pci_iobar_pfn(struct pci_dev *pdev, int bar, struct vm_area_struct *vma);
>  	(pci_resource_end((dev), (bar)) ? 				\
>  	 resource_size(pci_resource_n((dev), (bar))) : 0)
>  
> -#define __pci_dev_for_each_res0(dev, res, ...)				\
> -	for (unsigned int __b = 0;					\
> -	     res = pci_resource_n(dev, __b), __b < PCI_NUM_RESOURCES;	\
> +#define __pci_dev_for_each_res0(dev, res, ...)					\
> +	for (unsigned int __b = 0;						\
> +	     __b < PCI_NUM_RESOURCES && (res = pci_resource_n(dev, __b));	\
>  	     __b++)
>  
> -#define __pci_dev_for_each_res1(dev, res, __b)				\
> -	for (__b = 0;							\
> -	     res = pci_resource_n(dev, __b), __b < PCI_NUM_RESOURCES;	\
> +#define __pci_dev_for_each_res1(dev, res, __b)					\
> +	for (__b = 0;								\
> +	     __b < PCI_NUM_RESOURCES && (res = pci_resource_n(dev, __b));	\
>  	     __b++)
>  
>  #define pci_dev_for_each_resource(dev, res, ...)			\
> -- 
> 2.40.0.1.gaa8946217a0b
>