[Virtio-fs] [PATCH 1/3] posic_acl: Add a helper determine if SGID should be cleared

[Andreas Grünbacher]

Hi,

Am Fr., 19. März 2021 um 20:58 Uhr schrieb Vivek Goyal <vgoyal at redhat.com>:
> posix_acl_update_mode() determines what's the equivalent mode and if SGID
> needs to be cleared or not. I need to make use of this code in fuse
> as well. Fuse will send this information to virtiofs file server and
> file server will take care of clearing SGID if it needs to be done.
>
> Hence move this code in a separate helper so that more than one place
> can call into it.
>
> Cc: Jan Kara <jack at suse.cz>
> Cc: Andreas Gruenbacher <agruenba at redhat.com>
> Cc: Alexander Viro <viro at zeniv.linux.org.uk>
> Signed-off-by: Vivek Goyal <vgoyal at redhat.com>
> ---
>  fs/posix_acl.c            |  3 +--
>  include/linux/posix_acl.h | 11 +++++++++++
>  2 files changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/fs/posix_acl.c b/fs/posix_acl.c
> index f3309a7edb49..2d62494c4a5b 100644
> --- a/fs/posix_acl.c
> +++ b/fs/posix_acl.c
> @@ -684,8 +684,7 @@ int posix_acl_update_mode(struct user_namespace *mnt_userns,
>                 return error;
>         if (error == 0)
>                 *acl = NULL;
> -       if (!in_group_p(i_gid_into_mnt(mnt_userns, inode)) &&
> -           !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID))
> +       if (posix_acl_mode_clear_sgid(mnt_userns, inode))
>                 mode &= ~S_ISGID;
>         *mode_p = mode;
>         return 0;
> diff --git a/include/linux/posix_acl.h b/include/linux/posix_acl.h
> index 307094ebb88c..073c5e546de3 100644
> --- a/include/linux/posix_acl.h
> +++ b/include/linux/posix_acl.h
> @@ -59,6 +59,17 @@ posix_acl_release(struct posix_acl *acl)
>  }
>
>
> +static inline bool
> +posix_acl_mode_clear_sgid(struct user_namespace *mnt_userns,
> +                         struct inode *inode)
> +{
> +       if (!in_group_p(i_gid_into_mnt(mnt_userns, inode)) &&
> +           !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID))
> +               return true;
> +
> +       return false;

That's just

return !in_group_p(i_gid_into_mnt(mnt_userns, inode)) &&
    !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID);

The same pattern we have in posix_acl_update_mode also exists in
setattr_copy and inode_init_owner, and almost the same pattern exists
in setattr_prepare, so can this be cleaned up as well? The function
also isn't POSIX ACL specific, so the function name is misleading.

> +}
> +
>  /* posix_acl.c */
>
>  extern void posix_acl_init(struct posix_acl *, int);
> --
> 2.25.4

Thanks,
Andreas