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

On Mon, Jan 20, 2025 at 04:26:42PM +0000, Alejandro Lucero Palau wrote:

On 1/20/25 16:16, Alejandro Lucero Palau wrote:

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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:

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On 1/18/25 02:03, Dan Williams wrote:

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alejandro.lucero-palau@ wrote:

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From: Alejandro Lucero <redacted>

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 <redacted>
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 <redacted>
---
  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/ (local)
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?

-- Alison

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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 ...

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Did you audit existing callers?