Re: [PATCH] nfsd: inherit required unset default acls from effective set

["Andreas Grünbacher" <andreas.gruenbacher@gmail.com>]

Am Mi., 19. Juli 2023 um 23:22 Uhr schrieb Andreas Grünbacher
<andreas.gruenbacher@gmail.com>:
>
> Hi Jeff,
>
> this patch seems useful, thanks.
>
> Am Mi., 19. Juli 2023 um 19:56 Uhr schrieb Jeff Layton <jlayton@kernel.org>:
> > A well-formed NFSv4 ACL will always contain OWNER@/GROUP@/EVERYONE@
> > ACEs, but there is no requirement for inheritable entries for those
> > entities. POSIX ACLs must always have owner/group/other entries, even for a
> > default ACL.
>
> NFSv4 ACLs actually don't *need* to have OWNER@/GROUP@/EVERYONE@
> entries; that's merely a result of translating POSIX ACLs (or file
> modes) to NFSv4 ACLs.
>
> > nfsd builds the default ACL from inheritable ACEs, but the current code
> > just leaves any unspecified ACEs zeroed out. The result is that adding a
> > default user or group ACE to an inode can leave it with unwanted deny
> > entries.
> >
> > For instance, a newly created directory with no acl will look something
> > like this:
> >
> >         # NFSv4 translation by server
> >         A::OWNER@:rwaDxtTcCy
> >         A::GROUP@:rxtcy
> >         A::EVERYONE@:rxtcy
> >
> >         # POSIX ACL of underlying file
> >         user::rwx
> >         group::r-x
> >         other::r-x
> >
> > ...if I then add new v4 ACE:
> >
> >         nfs4_setfacl -a A:fd:1000:rwx /mnt/local/test
> >
> > ...I end up with a result like this today:
> >
> >         user::rwx
> >         user:1000:rwx
> >         group::r-x
> >         mask::rwx
> >         other::r-x
> >         default:user::---
> >         default:user:1000:rwx
> >         default:group::---
> >         default:mask::rwx
> >         default:other::---
> >
> >         A::OWNER@:rwaDxtTcCy
> >         A::1000:rwaDxtcy
> >         A::GROUP@:rxtcy
> >         A::EVERYONE@:rxtcy
> >         D:fdi:OWNER@:rwaDx
> >         A:fdi:OWNER@:tTcCy
> >         A:fdi:1000:rwaDxtcy
> >         A:fdi:GROUP@:tcy
> >         A:fdi:EVERYONE@:tcy
> >
> > ...which is not at all expected. Adding a single inheritable allow ACE
> > should not result in everyone else losing access.
> >
> > The setfacl command solves a silimar issue by copying owner/group/other
> > entries from the effective ACL when none of them are set:
> >
> >     "If a Default ACL entry is created, and the  Default  ACL  contains  no
> >      owner,  owning group,  or  others  entry,  a  copy of the ACL owner,
> >      owning group, or others entry is added to the Default ACL.
> >
> > Having nfsd do the same provides a more sane result (with no deny ACEs
> > in the resulting set):
> >
> >         user::rwx
> >         user:1000:rwx
> >         group::r-x
> >         mask::rwx
> >         other::r-x
> >         default:user::rwx
> >         default:user:1000:rwx
> >         default:group::r-x
> >         default:mask::rwx
> >         default:other::r-x
> >
> >         A::OWNER@:rwaDxtTcCy
> >         A::1000:rwaDxtcy
> >         A::GROUP@:rxtcy
> >         A::EVERYONE@:rxtcy
> >         A:fdi:OWNER@:rwaDxtTcCy
> >         A:fdi:1000:rwaDxtcy
> >         A:fdi:GROUP@:rxtcy
> >         A:fdi:EVERYONE@:rxtcy
>
> This resulting NFSv4 ACL is still rather dull; we end up with an
> inherit-only entry for each effective entry. Those could all be
> combined, resulting in:
>
>          A:fd:OWNER@:rwaDxtTcCy
>          A:fd:1000:rwaDxtcy
>          A:fd:GROUP@:rxtcy
>          A:fd:EVERYONE@:rxtcy
>
> This will be the common case, so maybe matching entry pairs can either
> be recombined or not generated in the first place as a further
> improvement.
>
> > Link: https://bugzilla.redhat.com/show_bug.cgi?id=2136452
> > Reported-by: Ondrej Valousek <ondrej.valousek@diasemi.com>
> > Suggested-by: Andreas Gruenbacher <agruen@redhat.com>
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> >  fs/nfsd/nfs4acl.c | 32 +++++++++++++++++++++++++++++---
> >  1 file changed, 29 insertions(+), 3 deletions(-)
> >
> > diff --git a/fs/nfsd/nfs4acl.c b/fs/nfsd/nfs4acl.c
> > index 518203821790..64e45551d1b6 100644
> > --- a/fs/nfsd/nfs4acl.c
> > +++ b/fs/nfsd/nfs4acl.c
> > @@ -441,7 +441,8 @@ struct posix_ace_state_array {
> >   * calculated so far: */
> >
> >  struct posix_acl_state {
> > -       int empty;
> > +       bool empty;
> > +       unsigned char valid;
>
> Hmm, "valid" is a bitmask here but it only matters whether it is zero.
> Shouldn't a bool be good enough? Also, this variable indicates whether
> special "who" values are present (and which), so the name "valid"
> probably isn't the best choice.
>
> >         struct posix_ace_state owner;
> >         struct posix_ace_state group;
> >         struct posix_ace_state other;
> > @@ -457,7 +458,7 @@ init_state(struct posix_acl_state *state, int cnt)
> >         int alloc;
> >
> >         memset(state, 0, sizeof(struct posix_acl_state));
> > -       state->empty = 1;
> > +       state->empty = true;
> >         /*
> >          * In the worst case, each individual acl could be for a distinct
> >          * named user or group, but we don't know which, so we allocate
> > @@ -624,7 +625,7 @@ static void process_one_v4_ace(struct posix_acl_state *state,
> >         u32 mask = ace->access_mask;
> >         int i;
> >
> > -       state->empty = 0;
> > +       state->empty = false;
> >
> >         switch (ace2type(ace)) {
> >         case ACL_USER_OBJ:
> > @@ -633,6 +634,7 @@ static void process_one_v4_ace(struct posix_acl_state *state,
> >                 } else {
> >                         deny_bits(&state->owner, mask);
> >                 }
> > +               state->valid |= ACL_USER_OBJ;
> >                 break;
> >         case ACL_USER:
> >                 i = find_uid(state, ace->who_uid);
> > @@ -655,6 +657,7 @@ static void process_one_v4_ace(struct posix_acl_state *state,
> >                         deny_bits_array(state->users, mask);
> >                         deny_bits_array(state->groups, mask);
> >                 }
> > +               state->valid |= ACL_GROUP_OBJ;
> >                 break;
> >         case ACL_GROUP:
> >                 i = find_gid(state, ace->who_gid);
> > @@ -686,6 +689,7 @@ static void process_one_v4_ace(struct posix_acl_state *state,
> >                         deny_bits_array(state->users, mask);
> >                         deny_bits_array(state->groups, mask);
> >                 }
> > +               state->valid |= ACL_OTHER;
> >         }
> >  }
> >
> > @@ -726,6 +730,28 @@ static int nfs4_acl_nfsv4_to_posix(struct nfs4_acl *acl,
> >                 if (!(ace->flag & NFS4_ACE_INHERIT_ONLY_ACE))
> >                         process_one_v4_ace(&effective_acl_state, ace);
> >         }
> > +
> > +       /*
> > +        * At this point, the default ACL may have zeroed-out entries for owner,
> > +        * group and other. That usually results in a non-sensical resulting ACL
> > +        * that denies all access except to any ACE that was explicitly added.
> > +        *
> > +        * The setfacl command solves a similar problem with this logic:
> > +        *
> > +        * "If  a  Default  ACL  entry is created, and the Default ACL contains
> > +        *  no owner, owning group, or others entry,  a  copy of  the  ACL
> > +        *  owner, owning group, or others entry is added to the Default ACL."
> > +        *
> > +        * If none of the requisite ACEs were set, and some explicit user or group
> > +        * ACEs were, copy the requisite entries from the effective set.
> > +        */
> > +       if (!default_acl_state.valid &&
> > +           (default_acl_state.users->n || default_acl_state.groups->n)) {
> > +               default_acl_state.owner = effective_acl_state.owner;
> > +               default_acl_state.group = effective_acl_state.group;
> > +               default_acl_state.other = effective_acl_state.other;
> > +       }
> > +

The other thing I'm wondering about is whether it would make more
sense to fake up for missing entries individually as setfacl does:

http://git.savannah.nongnu.org/cgit/acl.git/tree/tools/do_set.c#n368

> >         *pacl = posix_state_to_acl(&effective_acl_state, flags);
> >         if (IS_ERR(*pacl)) {
> >                 ret = PTR_ERR(*pacl);
> >
> > ---
> > base-commit: 9d985ab8ed33176c3c0380b7de589ea2ae51a48d
> > change-id: 20230719-nfsd-acl-5ab61537e4e6
> >
> > Best regards,
> > --
> > Jeff Layton <jlayton@kernel.org>

Thanks,
Andreas