linux-kernel - Re: [PATCH] drivers/xen: avoid out-of-range write in xen_add

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Date:	Mon, 07 Jan 2013 16:20:01 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Nickolai Zeldovich" <nickolai@...il.mit.edu>,
	<xen-devel@...ts.xensource.com>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>
Cc:	"Jeremy Fitzhardinge" <jeremy@...p.org>,
	<virtualization@...ts.linux-foundation.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drivers/xen: avoid out-of-range write in
 xen_add_device

>>> On 07.01.13 at 16:08, Konrad Rzeszutek Wilk <konrad.wilk@...cle.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@...il.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
>> 



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