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

[Chuck Lever III]

> On Jul 19, 2023, at 1:49 PM, Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> 
> 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.
> 
> 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
> 
> Link: https://bugzilla.redhat.com/show_bug.cgi?id=2136452
> Reported-by: Ondrej Valousek <ondrej.valousek@xxxxxxxxxxx>
> Suggested-by: Andreas Gruenbacher <agruen@xxxxxxxxxx>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>

As you pointed out in the bug report, there is not much testing
infrastructure for NFSv4 ACLs. It will be hard to tell in
advance if this change results in a behavior regression.

On the other hand, I'm not sure we have a large cohort of
NFSv4 ACL users on Linux.

I can certainly apply this to nfsd-next at least for a few
weeks to see if anyone yelps.


> ---
> 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;
> 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;
> + }
> +
> *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@xxxxxxxxxx>
> 

--
Chuck Lever