Re: [PATCH] vfs: transitive upgrade restrictions for fds

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Mar 23, 2026 at 11:00:22PM +0100, Jori Koolstra wrote:
> Add upgrade restrictions to openat2(). Extend struct open_how to allow
> setting transitive restrictions on using file descriptors to open other
> files. A use case for this feature is to block services or containers
> from re-opening/upgrading an O_PATH file descriptor through e.g.
> /proc/<pid>/fd/<nr as O_WRONLY.
> 
> The idea for this features comes form the UAPI group kernel feature idea
> list [1].
> 
> [1] https://github.com/uapi-group/kernel-features?tab=readme-ov-file#upgrade-masks-in-openat2
> 
> Signed-off-by: Jori Koolstra <jkoolstra@xs4all.nl>
> ---
>  fs/file_table.c                  |  2 ++
>  fs/internal.h                    |  1 +
>  fs/namei.c                       | 38 ++++++++++++++++++++++++++++----
>  fs/open.c                        |  9 ++++++++
>  fs/proc/base.c                   | 24 ++++++++++++++------
>  fs/proc/fd.c                     |  6 ++++-
>  fs/proc/internal.h               |  4 +++-
>  include/linux/fcntl.h            |  6 ++++-
>  include/linux/fs.h               |  1 +
>  include/linux/namei.h            | 15 ++++++++++++-
>  include/uapi/asm-generic/fcntl.h |  4 ++++
>  include/uapi/linux/openat2.h     |  1 +
>  12 files changed, 96 insertions(+), 15 deletions(-)

Any chance to get a test for this as well to know if this keeps working
(or works at all)?

>  /*
>   * Helper to directly jump to a known parsed path from ->get_link,
>   * caller must have taken a reference to path beforehand.
>   */
> -int nd_jump_link(const struct path *path)
> +int nd_jump_link_how(const struct path *path, const struct jump_how how)

Shouldn't that be "const struct jump_how *how"?

Or do you really want to pass this structure on the stack?

thanks,

greg k-h