Re: [PATCH v2] nfsd: inherit required unset default acls from effective set

[Chuck Lever]

On Mon, Jul 24, 2023 at 08:13:05AM -0400, Jeff Layton 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
> 
> Reported-by: Ondrej Valousek <ondrej.valousek@xxxxxxxxxxx>
> Closes: https://bugzilla.redhat.com/show_bug.cgi?id=2136452
> Suggested-by: Andreas Gruenbacher <agruenba@xxxxxxxxxx>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
> Changes in v2:
> - always set missing ACEs whenever default ACL has any ACEs that are
>   explicitly set. This better conforms to how setfacl works.
> - drop now-unneeded "empty" boolean
> - Link to v1: https://lore.kernel.org/r/20230719-nfsd-acl-v1-1-eb0faf3d2917@xxxxxxxxxx
> ---
>  fs/nfsd/nfs4acl.c | 32 ++++++++++++++++++++++++++++----
>  1 file changed, 28 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4acl.c b/fs/nfsd/nfs4acl.c
> index 518203821790..b931d4383517 100644
> --- a/fs/nfsd/nfs4acl.c
> +++ b/fs/nfsd/nfs4acl.c
> @@ -441,7 +441,7 @@ struct posix_ace_state_array {
>   * calculated so far: */
>  
>  struct posix_acl_state {
> -	int empty;
> +	unsigned char valid;
>  	struct posix_ace_state owner;
>  	struct posix_ace_state group;
>  	struct posix_ace_state other;
> @@ -457,7 +457,6 @@ init_state(struct posix_acl_state *state, int cnt)
>  	int alloc;
>  
>  	memset(state, 0, sizeof(struct posix_acl_state));
> -	state->empty = 1;
>  	/*
>  	 * 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
> @@ -500,7 +499,7 @@ posix_state_to_acl(struct posix_acl_state *state, unsigned int flags)
>  	 * and effective cases: when there are no inheritable ACEs,
>  	 * calls ->set_acl with a NULL ACL structure.
>  	 */
> -	if (state->empty && (flags & NFS4_ACL_TYPE_DEFAULT))
> +	if (!state->valid && (flags & NFS4_ACL_TYPE_DEFAULT))
>  		return NULL;
>  
>  	/*
> @@ -622,9 +621,10 @@ static void process_one_v4_ace(struct posix_acl_state *state,
>  				struct nfs4_ace *ace)
>  {
>  	u32 mask = ace->access_mask;
> +	short type = ace2type(ace);
>  	int i;
>  
> -	state->empty = 0;
> +	state->valid |= type;
>  
>  	switch (ace2type(ace)) {

Mechanical issue: the patch adds @type, but uses it just once.
The switch here also wants the value of ace2type(ace).


>  	case ACL_USER_OBJ:
> @@ -726,6 +726,30 @@ 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."
> +	 *
> +	 * Copy any missing ACEs from the effective set, if any ACEs were
> +	 * explicitly set.
> +	 */
> +	if (default_acl_state.valid) {
> +		if (!(default_acl_state.valid & ACL_USER_OBJ))
> +			default_acl_state.owner = effective_acl_state.owner;
> +		if (!(default_acl_state.valid & ACL_GROUP_OBJ))
> +			default_acl_state.group = effective_acl_state.group;
> +		if (!(default_acl_state.valid & ACL_OTHER))
> +			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: 7bfb36a2ee1d329a501ba4781db4145dc951c798
> change-id: 20230719-nfsd-acl-5ab61537e4e6
> 
> Best regards,
> -- 
> Jeff Layton <jlayton@xxxxxxxxxx>
> 

-- 
Chuck Lever