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SubjectRe: [PATCH v2 1/4] container_of: add container_of_const() that preserves const-ness of the pointer
Hi Greg,

On Mon, Dec 05, 2022 at 01:12:03PM +0100, Greg Kroah-Hartman wrote:
> container_of does not preserve the const-ness of a pointer that is
> passed into it, which can cause C code that passes in a const pointer to
> get a pointer back that is not const and then scribble all over the data
> in it. To prevent this, container_of_const() will preserve the const
> status of the pointer passed into it using the newly available _Generic()
> method.
>
> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
> Suggested-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
> v2: - removed one parameter, now matches container_of(), thanks to
> suggestion from Sakari
> - changed Jason's tag to suggested-by and reviewed-by
> - added Andy's tag

Thanks for the update. For the set:

Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>

>
> include/linux/container_of.h | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/include/linux/container_of.h b/include/linux/container_of.h
> index 2008e9f4058c..1d898f9158b4 100644
> --- a/include/linux/container_of.h
> +++ b/include/linux/container_of.h
> @@ -22,4 +22,17 @@
> "pointer type mismatch in container_of()"); \
> ((type *)(__mptr - offsetof(type, member))); })
>
> +/**
> + * container_of_const - cast a member of a structure out to the containing
> + * structure and preserve the const-ness of the pointer
> + * @ptr: the pointer to the member
> + * @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) \
> + _Generic(ptr, \
> + const typeof(*(ptr)) *: ((const type *)container_of(ptr, type, member)),\
> + default: ((type *)container_of(ptr, type, member)) \
> + )
> +
> #endif /* _LINUX_CONTAINER_OF_H */

--
Kind regards,

Sakari Ailus

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