nfsd: allow setting acls with unenforceable DENYs

We've been refusing ACLs that DENY permissions that we can't effectively
deny.  (For example, we can't deny permission to read attributes.)

Andreas points out that any DENY of Window's "read", "write", or
"modify" permissions would trigger this.  That would be annoying.

So maybe we should be a little less paranoid, and ignore entirely the
permissions that are meaningless to us.
Reported-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4acl.c

@@ -499,43 +499,13 @@ static inline void add_to_mask(struct posix_acl_state *state, struct posix_ace_s
 	state->mask.allow |= astate->allow;
 }
 
-/*
- * Certain bits (SYNCHRONIZE, DELETE, WRITE_OWNER, READ/WRITE_NAMED_ATTRS,
- * READ_ATTRIBUTES, READ_ACL) are currently unenforceable and don't translate
- * to traditional read/write/execute permissions.
- *
- * It's problematic to reject acls that use certain mode bits, because it
- * places the burden on users to learn the rules about which bits one
- * particular server sets, without giving the user a lot of help--we return an
- * error that could mean any number of different things.  To make matters
- * worse, the problematic bits might be introduced by some application that's
- * automatically mapping from some other acl model.
- *
- * So wherever possible we accept anything, possibly erring on the side of
- * denying more permissions than necessary.
- *
- * However we do reject *explicit* DENY's of a few bits representing
- * permissions we could never deny:
- */
-
-static inline int check_deny(u32 mask, int isowner)
-{
-	if (mask & (NFS4_ACE_READ_ATTRIBUTES | NFS4_ACE_READ_ACL))
-		return -EINVAL;
-	if (!isowner)
-		return 0;
-	if (mask & (NFS4_ACE_WRITE_ATTRIBUTES | NFS4_ACE_WRITE_ACL))
-		return -EINVAL;
-	return 0;
-}
-
 static struct posix_acl *
 posix_state_to_acl(struct posix_acl_state *state, unsigned int flags)
 {
 	struct posix_acl_entry *pace;
 	struct posix_acl *pacl;
 	int nace;
-	int i, error = 0;
+	int i;
 
 	/*
 	 * ACLs with no ACEs are treated differently in the inheritable
@@ -560,17 +530,11 @@ posix_state_to_acl(struct posix_acl_state *state, unsigned int flags)
 
 	pace = pacl->a_entries;
 	pace->e_tag = ACL_USER_OBJ;
-	error = check_deny(state->owner.deny, 1);
-	if (error)
-		goto out_err;
 	low_mode_from_nfs4(state->owner.allow, &pace->e_perm, flags);
 
 	for (i=0; i < state->users->n; i++) {
 		pace++;
 		pace->e_tag = ACL_USER;
-		error = check_deny(state->users->aces[i].perms.deny, 0);
-		if (error)
-			goto out_err;
 		low_mode_from_nfs4(state->users->aces[i].perms.allow,
 					&pace->e_perm, flags);
 		pace->e_uid = state->users->aces[i].uid;
@@ -579,18 +543,12 @@ posix_state_to_acl(struct posix_acl_state *state, unsigned int flags)
 
 	pace++;
 	pace->e_tag = ACL_GROUP_OBJ;
-	error = check_deny(state->group.deny, 0);
-	if (error)
-		goto out_err;
 	low_mode_from_nfs4(state->group.allow, &pace->e_perm, flags);
 	add_to_mask(state, &state->group);
 
 	for (i=0; i < state->groups->n; i++) {
 		pace++;
 		pace->e_tag = ACL_GROUP;
-		error = check_deny(state->groups->aces[i].perms.deny, 0);
-		if (error)
-			goto out_err;
 		low_mode_from_nfs4(state->groups->aces[i].perms.allow,
 					&pace->e_perm, flags);
 		pace->e_gid = state->groups->aces[i].gid;
@@ -605,15 +563,9 @@ posix_state_to_acl(struct posix_acl_state *state, unsigned int flags)
 
 	pace++;
 	pace->e_tag = ACL_OTHER;
-	error = check_deny(state->other.deny, 0);
-	if (error)
-		goto out_err;
 	low_mode_from_nfs4(state->other.allow, &pace->e_perm, flags);
 
 	return pacl;
-out_err:
-	posix_acl_release(pacl);
-	return ERR_PTR(error);
 }
 
 static inline void allow_bits(struct posix_ace_state *astate, u32 mask)