OpenLDAP配置MemberOf overlay时因权限不足无法加载数据库overlay的问题求助

我在编译安装的OpenLDAP 2.5.16上配置MemberOf overlay时遇到了权限问题，麻烦大家帮忙看看哪里出错了。

我是从源码编译的OpenLDAP 2.5.16，编译时加了--with-memberof选项，目前基础的数据库配置看起来是正常的：

执行slapcat查看配置库信息，得到以下内容：

dn: olcDatabase={1}mdb,cn=config
objectClass: olcDatabaseConfig
objectClass: olcMdbConfig
olcDatabase: {1}mdb
olcSuffix: dc=contoso,dc=com
olcAccess: {0}to attrs=userPassword  by anonymous auth  by self write  by * none
olcAccess: {1}to *  by dn.base="cn=admin,dc=contoso,dc=com" write  by self write  by * none
olcAddContentAcl: FALSE
olcLastMod: TRUE
olcLastBind: FALSE
olcMaxDerefDepth: 15
olcReadOnly: FALSE
olcRootDN: cn=admin,dc=contoso,dc=com
olcRootPW:: LKSkwema9kajkw32==

接下来我尝试给数据库添加MemberOf overlay，写了一个add_memberoff.ldif文件：

dn: olcOverlay=memberof,olcDatabase={1}mdb,cn=config
objectClass: olcOverlayConfig
objectClass: olcMemberOf
olcOverlay: memberof
olcMemberOfRefint: TRUE

然后用以下命令添加这个配置：

bin/ldapadd -x -D "cn=admin,dc=contoso,dc=com" -W -f add_memberoff.ldif

结果报错了：

adding new entry "olcOverlay=memberof,olcDatabase={1}mdb,cn=config"
ldap_add: Insufficient access (50)

查看OpenLDAP日志，相关内容如下：

65dca351.151db256 0x7eff2ffff6c0 conn=1028 fd=14 ACCEPT from IP=127.0.0.1:38524 (IP=0.0.0.0:389)
65dca351.151e9d47 0x7eff34c016c0 conn=1028 op=0 BIND dn="cn=admin,dc=contoso,dc=com" method=128
65dca351.1520796e 0x7eff34c016c0 conn=1028 op=0 BIND dn="cn=admin,dc=contoso,dc=com" mech=SIMPLE bind_ssf=0 ssf=0
65dca351.15219d56 0x7eff34c016c0 conn=1028 op=0 RESULT tag=97 err=0 qtime=0.000009 etime=0.000216 text=
65dca351.1523bd83 0x7eff2ffff6c0 conn=1028 op=1 ADD dn="olcOverlay=memberof,olcDatabase={1}mdb,cn=config"
65dca351.1524555d 0x7eff2ffff6c0 => access_allowed: add access to "olcOverlay=memberof,olcDatabase={1}mdb,cn=config" "entry" requested
65dca351.152486ca 0x7eff2ffff6c0 => acl_get: [1] attr entry
65dca351.1524a3c8 0x7eff2ffff6c0 => acl_mask: access to entry "olcOverlay=memberof,olcDatabase={1}mdb,cn=config", attr "entry" requested
65dca351.1524b9ef 0x7eff2ffff6c0 => acl_mask: to all values by "cn=admin,dc=contoso,dc=com", (=0)
65dca351.1524d378 0x7eff2ffff6c0 <= check a_dn_pat: *
65dca351.1524f2cf 0x7eff2ffff6c0 <= acl_mask: [1] applying none(=0) (stop)
65dca351.15250d85 0x7eff2ffff6c0 <= acl_mask: [1] mask: none(=0)
65dca351.1525270d 0x7eff2ffff6c0 => slap_access_allowed: add access denied by none(=0)
65dca351.15253c3d 0x7eff2ffff6c0 => access_allowed: no more rules
65dca351.15258f10 0x7eff2ffff6c0 conn=1028 op=1 RESULT tag=105 err=50 qtime=0.000009 etime=0.000137 text=
65dca351.1526fba1 0x7eff34c016c0 conn=1028 op=2 UNBIND
65dca351.152a5b85 0x7eff34c016c0 conn=1028 fd=14 closed

我实在搞不清楚哪里出问题了，有没有大佬能指点一下？

备注：内容来源于stack exchange，提问作者Smok