CentOS - Nov 2018 - sssd ldap_user_search_base filters with '#' characters in names

I'm trying to craft an ldap search filter for use with 
ldap_user_search_base in sssd.conf which is using Actice Directory (AD) 
as the back end on CentOS 7 clients

The filter looks for users that are memberOf a particular group - 
however, the group name start with a '#' character - i.e. in AD, the 
group name is listed as something like '#ABC XYZ'

But when I set ldap_user_search_base to something like:

  ldap_user_search_base = 
OU=Users,DC=Example,DC=com?subtree?(memberOf=CN=#ABC 
XYZ,OU=Groups,DC=Example,DC=com)

then 'getent passwd user' fails to return anything (for 'user'
that is
in that group)

However, when using the above syntax with a group name that doesn't 
start with a '#' character, then things work as expected

When I use ldapsearch, it reports that the user is a memberOf:

  memberOf: CN=\#ABC XYZ,OU=Groups,DC=Example,DC=com

But using the '\' in sssd.conf for the search filter cause sssd to error
with 'Invalid search filter' in the logs

Escaping the Escape ('\\') also gives 'Invalid search filter'

Does anyone know how to 'escape' special characters in search filters in
sssd.conf ?

Thanks

James Pearson

James Pearson wrote:
> 
> I'm trying to craft an ldap search filter for use with
> ldap_user_search_base in sssd.conf which is using Actice Directory (AD)
> as the back end on CentOS 7 clients
> 
> The filter looks for users that are memberOf a particular group -
> however, the group name start with a '#' character - i.e. in AD,
the
> group name is listed as something like '#ABC XYZ'
> 
> But when I set ldap_user_search_base to something like:
> 
>    ldap_user_search_base >
OU=Users,DC=Example,DC=com?subtree?(memberOf=CN=#ABC
> XYZ,OU=Groups,DC=Example,DC=com)
> 
> then 'getent passwd user' fails to return anything (for
'user' that is
> in that group)
> 
> However, when using the above syntax with a group name that doesn't
> start with a '#' character, then things work as expected
> 
> When I use ldapsearch, it reports that the user is a memberOf:
> 
>    memberOf: CN=\#ABC XYZ,OU=Groups,DC=Example,DC=com
> 
> But using the '\' in sssd.conf for the search filter cause sssd to
error
> with 'Invalid search filter' in the logs
> 
> Escaping the Escape ('\\') also gives 'Invalid search
filter'
> 
> Does anyone know how to 'escape' special characters in search
filters in
> sssd.conf ?
After going round in circles for a while - I managed to get this working

Turns out you can use the hexadecimal code for characters in an LDAP 
filter/search path/whatever - which is escaped via '\' followed by 2 
hexadecimal characters - so the following works:

  memberOf: CN=\5C#ABC XYZ,OU=Groups,DC=Example,DC=com

i.e. 5C is the character code for '\'

This also explains why I was getting 'Invalid search filter' previously,
as my use of '\' was followed by invalid hexadecimal characters ...

James Pearson