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Message-ID: <ZAjMeVHI1r8jFW/X@kroah.com>
Date: Wed, 8 Mar 2023 18:57:13 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: linux-kernel@...r.kernel.org, Jason Gunthorpe <jgg@...pe.ca>,
Sakari Ailus <sakari.ailus@...ux.intel.com>,
Matthew Wilcox <willy@...radead.org>,
Jason Gunthorpe <jgg@...dia.com>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
"Rafael J . Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH] container_of: add type safety
On Wed, Mar 08, 2023 at 12:35:03PM -0500, Michael S. Tsirkin wrote:
> Using a wrong member in container_of will result in an error.
> No so for container_of_const - it is just a cast so will
> happily give you a wrong pointer.
>
> Use logic from container_of to add safety.
>
> Cc: Jason Gunthorpe <jgg@...pe.ca>
> Cc: Sakari Ailus <sakari.ailus@...ux.intel.com>
> Cc: Matthew Wilcox (Oracle) <willy@...radead.org>
> Cc: Jason Gunthorpe <jgg@...dia.com>
> Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Cc: Sakari Ailus <sakari.ailus@...ux.intel.com>
> Cc: Rafael J. Wysocki <rafael@...nel.org>
> Link: https://lore.kernel.org/r/20221205121206.166576-1-gregkh@linuxfoundation.org
That's the wrong link, that's not this patch, that was an old patch.
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
I did not sign off on this. NEVER do that, you just made a legal
statement in my name, why?
Why did you not sign off on it?
totally confused...
> ---
> include/linux/container_of.h | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/container_of.h b/include/linux/container_of.h
> index 1d898f9158b4..5d87faf72e0a 100644
> --- a/include/linux/container_of.h
> +++ b/include/linux/container_of.h
> @@ -29,10 +29,13 @@
> * @type: the type of the container struct this is embedded in.
> * @member: the name of the member within the struct.
> */
> -#define container_of_const(ptr, type, member) \
> +#define container_of_const(ptr, type, member) ({ \
> + static_assert(__same_type(*(ptr), ((type *)0)->member) || \
> + __same_type(*(ptr), void), \
> + "pointer type mismatch in container_of()"); \
Why is this needed because:
> _Generic(ptr, \
> const typeof(*(ptr)) *: ((const type *)container_of(ptr, type, member)),\
> default: ((type *)container_of(ptr, type, member)) \
container_of() is used here, so shouldn't the assert trigger there if
you get things wrong?
So why is this change needed at all?
thanks,
greg k-h
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