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

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Message-ID: <20210323093233.iyl4k6x432ytb72c@wittgenstein>
Date:   Tue, 23 Mar 2021 10:32:33 +0100
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Vivek Goyal <vgoyal@...hat.com>
Cc:     Christian Brauner <christian.brauner@...onical.com>,
        Andreas Grünbacher 
        <andreas.gruenbacher@...il.com>,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        virtio-fs@...hat.com, Miklos Szeredi <miklos@...redi.hu>,
        lhenriques@...e.de, dgilbert@...hat.com,
        Seth Forshee <seth.forshee@...onical.com>,
        Jan Kara <jack@...e.cz>,
        Andreas Gruenbacher <agruenba@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH 1/3] posic_acl: Add a helper determine if SGID should be
 cleared

On Mon, Mar 22, 2021 at 01:01:11PM -0400, Vivek Goyal wrote:
> On Sat, Mar 20, 2021 at 11:03:22AM +0100, Christian Brauner wrote:
> > 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@...hat.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@...e.cz>
> > > > Cc: Andreas Gruenbacher <agruenba@...hat.com>
> > > > Cc: Alexander Viro <viro@...iv.linux.org.uk>
> > > > Signed-off-by: Vivek Goyal <vgoyal@...hat.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.
> 
> IIUC, suggestion is that I should write a VFS helper (and not posix
> acl helper) and use that helper at other places too in the code. 

If there are other callers outside of acls (which should be iirc) then
yes.

> 
> I will do that and post in a separate patch series.

Yeah, I think that makes more sense to have this be a separate change
instead of putting it together with the fuse change if it touches more
than one place.

Thanks!
Christian