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

[Christian Brauner <christian.brauner@canonical.com>]

On Fri, Mar 19, 2021 at 11:42:48PM +0100, Andreas Grünbacher wrote:
> Hi,
> 
> Am Fr., 19. März 2021 um 20:58 Uhr schrieb Vivek Goyal <vgoyal@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@suse.cz>
> > Cc: Andreas Gruenbacher <agruenba@redhat.com>
> > Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> > Signed-off-by: Vivek Goyal <vgoyal@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.

Good idea but that should probably be spun into a separate patchset that
only touches the vfs parts.

Christian