Re: [PATCH 03/10] fs: tweak fsuidgid_has_mapping()

[Amir Goldstein <amir73il@gmail.com>]

On Tue, Nov 23, 2021 at 3:29 PM Christian Brauner <brauner@kernel.org> wrote:
>
> From: Christian Brauner <christian.brauner@ubuntu.com>
>
> If the caller's fs{g,u}id aren't mapped in the mount's idmapping we can
> return early and skip the check whether the mapped fs{g,u}id also have a
> mapping in the filesystem's idmapping. If the fs{g,u}id aren't mapped in
> the mount's idmapping they consequently can't be mapped in the
> filesystem's idmapping. So there's no point in checking that.
>
> Cc: Seth Forshee <sforshee@digitalocean.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> CC: linux-fsdevel@vger.kernel.org
> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
> ---
Reviewed-by: Amir Goldstein <amir73il@gmail.com>

>  include/linux/fs.h | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index eb69e8b035fa..161b5936094e 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1695,10 +1695,18 @@ static inline void inode_fsgid_set(struct inode *inode,
>  static inline bool fsuidgid_has_mapping(struct super_block *sb,
>                                         struct user_namespace *mnt_userns)
>  {
> -       struct user_namespace *s_user_ns = sb->s_user_ns;
> +       struct user_namespace *fs_userns = sb->s_user_ns;
> +       kuid_t kuid;
> +       kgid_t kgid;
>
> -       return kuid_has_mapping(s_user_ns, mapped_fsuid(mnt_userns)) &&
> -              kgid_has_mapping(s_user_ns, mapped_fsgid(mnt_userns));
> +       kuid = mapped_fsuid(mnt_userns);
> +       if (!uid_valid(kuid))
> +               return false;
> +       kgid = mapped_fsgid(mnt_userns);
> +       if (!gid_valid(kgid))
> +               return false;
> +       return kuid_has_mapping(fs_userns, kuid) &&
> +              kgid_has_mapping(fs_userns, kgid);
>  }
>
>  extern struct timespec64 current_time(struct inode *inode);
> --
> 2.30.2
>