Re: [PATCH] drivers/xen: avoid out-of-range write in xen_add_device

Re: [PATCH] drivers/xen: avoid out-of-range write in xen_add_device

[Konrad Rzeszutek Wilk]

On Sat, Jan 05, 2013 at 02:18:46PM -0500, Nickolai Zeldovich wrote:
> xen_add_device() in drivers/xen/pci.c allocates a struct
> physdev_pci_device_add on the stack and then writes to optarr[0].
> The previous declaration of struct physdev_pci_device_add contained
> a zero-length optarr[] array, presumably assuming it will be allocated
> with kmalloc with a suitable number of trailing elements, but the code in
> xen_add_device() as a result wrote past the end of the (stack-allocated)
> data structure.
> 
> Since xen_add_device() is the only use of struct physdev_pci_device_add
> in the kernel, turn optarr[] into a single-element array instead.
> 

Lets include Jan and Xen-devel on this email - as this is also changing
the official header that is used in Xen.

> Signed-off-by: Nickolai Zeldovich <nickolai@csail.mit.edu>
> ---
>  include/xen/interface/physdev.h |    6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/include/xen/interface/physdev.h b/include/xen/interface/physdev.h
> index 1844d31..24fd218 100644
> --- a/include/xen/interface/physdev.h
> +++ b/include/xen/interface/physdev.h
> @@ -242,11 +242,7 @@ struct physdev_pci_device_add {
>          uint8_t bus;
>          uint8_t devfn;
>      } physfn;
> -#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L
> -    uint32_t optarr[];
> -#elif defined(__GNUC__)
> -    uint32_t optarr[0];
> -#endif
> +    uint32_t optarr[1];
>  };
>  
>  #define PHYSDEVOP_pci_device_remove     26
> -- 
> 1.7.10.4
> 

Re: [PATCH] drivers/xen: avoid out-of-range write in xen_add_device

[Jan Beulich]

>>> On 07.01.13 at 16:08, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote:
> On Sat, Jan 05, 2013 at 02:18:46PM -0500, Nickolai Zeldovich wrote:
>> xen_add_device() in drivers/xen/pci.c allocates a struct
>> physdev_pci_device_add on the stack and then writes to optarr[0].
>> The previous declaration of struct physdev_pci_device_add contained
>> a zero-length optarr[] array, presumably assuming it will be allocated
>> with kmalloc with a suitable number of trailing elements, but the code in
>> xen_add_device() as a result wrote past the end of the (stack-allocated)
>> data structure.
>> 
>> Since xen_add_device() is the only use of struct physdev_pci_device_add
>> in the kernel, turn optarr[] into a single-element array instead.
>> 
> 
> Lets include Jan and Xen-devel on this email - as this is also changing
> the official header that is used in Xen.

Correct - for that reason it is not the header that needs changing
here, but the consumer of the header. I have to admit that I find
it odd that the compiler allows automatic variables of variable size
types without warning - otherwise this wouldn't have gone
unnoticed.

Jan

>> Signed-off-by: Nickolai Zeldovich <nickolai@csail.mit.edu>
>> ---
>>  include/xen/interface/physdev.h |    6 +-----
>>  1 file changed, 1 insertion(+), 5 deletions(-)
>> 
>> diff --git a/include/xen/interface/physdev.h b/include/xen/interface/physdev.h
>> index 1844d31..24fd218 100644
>> --- a/include/xen/interface/physdev.h
>> +++ b/include/xen/interface/physdev.h
>> @@ -242,11 +242,7 @@ struct physdev_pci_device_add {
>>          uint8_t bus;
>>          uint8_t devfn;
>>      } physfn;
>> -#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L
>> -    uint32_t optarr[];
>> -#elif defined(__GNUC__)
>> -    uint32_t optarr[0];
>> -#endif
>> +    uint32_t optarr[1];
>>  };
>>  
>>  #define PHYSDEVOP_pci_device_remove     26
>> -- 
>> 1.7.10.4
>>