netdev - Re: [PATCH v9 10/27] resource: harden resource

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Message-ID: <5180d24d-db23-e489-b27f-8575b78b5172@amd.com>
Date: Wed, 22 Jan 2025 09:41:35 +0000
From: Alejandro Lucero Palau <alucerop@....com>
To: Dan Williams <dan.j.williams@...el.com>, alejandro.lucero-palau@....com,
 linux-cxl@...r.kernel.org, netdev@...r.kernel.org, edward.cree@....com,
 davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
 edumazet@...gle.com, dave.jiang@...el.com
Subject: Re: [PATCH v9 10/27] resource: harden resource_contains


On 1/21/25 23:01, Dan Williams wrote:
> Alejandro Lucero Palau wrote:
>> On 1/18/25 02:03, Dan Williams wrote:
>>> alejandro.lucero-palau@ wrote:
>>>> From: Alejandro Lucero <alucerop@....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@....com>
>>>> Suggested-by: Alison Schofield <alison.schofield@...el.com>
>>>> Reviewed-by: Alison Schofield <alison.schofield@...el.com>
>>>> Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
>>>> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.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.
> The regression risk is not philosophic relative to how long this
> function has returned 'true' for the size == 0 case.


Would not this regression be a good thing?

Because I argue that is not the right thing to do.


>> But maybe it is just  my lack of understanding and there exists a good
>> reason for this possibility.
> Questions like the following are good to answer when changing long
> standing behavior:
>
> Did you look at any other resource_contains() user to get a sense of
> that regression risk?
>
> Is the benefit to changing this higher than that risk?
>
> Would it be better to just document the expectation that the caller
> should only pass non-zero sized resources to this function?