From 64f6a5d1922bf6d2b2d845de20d4563a6f328e2d Mon Sep 17 00:00:00 2001 From: Greg Kroah-Hartman Date: Mon, 5 Dec 2022 13:12:03 +0100 Subject: [PATCH] container_of: add container_of_const() that preserves const-ness of the pointer 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 Suggested-by: Sakari Ailus Reviewed-by: Matthew Wilcox (Oracle) Reviewed-by: Jason Gunthorpe Reviewed-by: Andy Shevchenko Reviewed-by: Sakari Ailus Acked-by: Rafael J. Wysocki Link: https://lore.kernel.org/r/20221205121206.166576-1-gregkh@linuxfoundation.org Signed-off-by: Greg Kroah-Hartman --- 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 2008e9f..1d898f9 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 */ -- 2.7.4