[PATCH v2 07/25] capability: provide a helper for converting vfs_caps to xattr for userspace

[Christian Brauner]

On Wed, Feb 21, 2024 at 03:24:38PM -0600, Seth Forshee (DigitalOcean) wrote:
> cap_inode_getsecurity() implements a handful of policies for capability
> xattrs read by userspace:
> 
>  - It returns EINVAL if the on-disk capability is in v1 format.
> 
>  - It masks off all bits in magic_etc except for the version and
>    VFS_CAP_FLAGS_EFFECTIVE.
> 
>  - v3 capabilities are converted to v2 format if the rootid returned to
>    userspace would be 0 or if the rootid corresponds to root in an
>    ancestor user namespace.
> 
>  - It returns EOVERFLOW for a v3 capability whose rootid does not map to
>    a valid id in current_user_ns() or to root in an ancestor namespace.
> 
> These policies must be maintained when converting vfs_caps to an xattr
> for userspace. Provide a vfs_caps_to_user_xattr() helper which will
> enforce these policies.
> 
> Signed-off-by: Seth Forshee (DigitalOcean) <sforshee at kernel.org>
> ---

Looks good,
Reviewed-by: Christian Brauner <brauner at kernel.org>