Re: [PATCH v9 10/27] resource: harden resource_contains

Alejandro Lucero Palau
2025-01-22T09:37:56Z

On 1/21/25 20:38, Alison Schofield wrote:
> On Mon, Jan 20, 2025 at 04:26:42PM +0000, Alejandro Lucero Palau wrote:
>> On 1/20/25 16:16, Alejandro Lucero Palau wrote:
>>> Adding Bjorn to the thread. Not sure if he just gets the email being in
>>> an Acked-by line.
>>>
>>>
>>> On 1/20/25 16:10, Alejandro Lucero Palau wrote:
>>>> On 1/18/25 02:03, Dan Williams wrote:
>>>>> alejandro.lucero-palau@ wrote:
>>>>>> From: Alejandro Lucero <alucerop@amd.com>
>>>>>>
>>>>>> While resource_contains checks for IORESOURCE_UNSET flag for the
>>>>>> resources given, if r1 was initialized with 0 size, the function
>>>>>> returns a false positive. This is so because resource start and
>>>>>> end fields are unsigned with end initialised to size - 1 by current
>>>>>> resource macros.
>>>>>>
>>>>>> Make the function to check for the resource size for both resources
>>>>>> since r2 with size 0 should not be considered as valid for
>>>>>> the function
>>>>>> purpose.
>>>>>>
>>>>>> Signed-off-by: Alejandro Lucero <alucerop@amd.com>
>>>>>> Suggested-by: Alison Schofield <alison.schofield@intel.com>
>>>>>> Reviewed-by: Alison Schofield <alison.schofield@intel.com>
>>>>>> Acked-by: Bjorn Helgaas <bhelgaas@google.com>
>>>>>> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>>>>>> ---
>>>>>>   include/linux/ioport.h | 2 ++
>>>>>>   1 file changed, 2 insertions(+)
>>>>>>
>>>>>> diff --git a/include/linux/ioport.h b/include/linux/ioport.h
>>>>>> index 5385349f0b8a..7ba31a222536 100644
>>>>>> --- a/include/linux/ioport.h
>>>>>> +++ b/include/linux/ioport.h
>>>>>> @@ -296,6 +296,8 @@ static inline unsigned long
>>>>>> resource_ext_type(const struct resource *res)
>>>>>>   /* True iff r1 completely contains r2 */
>>>>>>   static inline bool resource_contains(const struct resource
>>>>>> *r1, const struct resource *r2)
>>>>>>   {
>>>>>> +    if (!resource_size(r1) || !resource_size(r2))
>>>>>> +        return false;
>>>>> I just worry that some code paths expect the opposite, that it is ok to
>>>>> pass zero size resources and get a true result.
>>>>
>>>> That is an interesting point, I would say close to philosophic
>>>> arguments. I guess you mean the zero size resource being the one
>>>> that is contained inside the non-zero one, because the other option
>>>> is making my vision blurry. In fact, even that one makes me feel
>>>> trapped in a window-less room, in summer, with a bunch of
>>>> economists, I mean philosophers, and my phone without signal for
>>>> emergency calls.
>>>>
>> I forgot to make my strongest point :-). If someone assumes it is or it
>> should be true a zero-size resource is contained inside a non zero-size
>> resource, we do not need to call a function since it is always true
>> regardless of the non zero-size resource ... that headache is starting again
>> ...
>>
>>
> Maybe start using IORESOURCE_UNSET flag -
>
> Looking back on when we first discussed this -
> https://lore.kernel.org/linux-cxl/Zz-fVWhTOFG4Nek-@aschofie-mobl2.lan/
> where the thought was that checking for zero was helpful to all.
>
> If this path starts using the IORESOURCE_UNSET flag can it accomplish
> the same thing? No need to touch resource_contains().
>
> Is that an option?

I think those are not mutually exclusive. The main reason for this
change is hardening, in this particular case a resource
definition/initialization apparently right, leading to this function
returning something it should not. Even if you suggest the solution is
hardening the resource definition/initialization, what I agree it is
another thing to look at, I would leave this extra check here for
correctness. This is assuming there is no case for what Dan mentioned
and therefore auditing the callers being necessary.

> -- Alison
>
>
>
>>>> But maybe it is just  my lack of understanding and there exists a
>>>> good reason for this possibility.
>>>>
>>>>
>>>> Bjorn, I guess the ball is in your side ...
>>>>
>>>>> Did you audit existing callers?