idmap_script — Samba's idmap_script Backend for Winbind
The idmap_script plugin is a substitute for the idmap_tdb2 backend used by winbindd for storing SID/uid/gid mapping tables in clustered environments with Samba and CTDB. It is a read only backend that uses a script to perform mapping.
It was developed out of the idmap_tdb2 back end and does not store SID/uid/gid mappings in a TDB, since the winbind_cache tdb will store the mappings once they are provided.
Defines the available matching uid and gid range for which the backend is authoritative.
This option can be used to configure an external program for performing id mappings.
The tdb2 idmap backend supports an external program for performing id mappings
through the smb.conf option
idmap config * : script or
its deprecated legacy form
idmap : script.
The mappings obtained by the script are then stored in the idmap tdb2 database instead of mappings created by the incrementing id counters. It is therefore important that the script covers the complete range of SIDs that can be passed in for SID to Unix ID mapping, since otherwise SIDs unmapped by the script might get mapped to IDs that had previously been mapped by the script.
The script should accept the following command line options.
SIDTOID S-1-xxxx IDTOSID UID xxxx IDTOSID GID xxxx IDTOSID XID xxxx
And it should return one of the following responses as a single line of text.
UID:yyyy GID:yyyy XID:yyyy SID:ssss ERR:yyyy
XID indicates that the ID returned should be both a UID and a GID. That is, it requests an ID_TYPE_BOTH, but it is ultimately up to the script whether or not it can honor that request. It can choose to return a UID or a GID mapping only.
This example shows how script is used as a the default idmap backend using an external program via the script parameter:
[global] idmap config * : backend = script idmap config * : range = 1000000-2000000 idmap config * : script = /usr/local/samba/bin/idmap_script.sh
This shows a simple script to partially perform the task:
#!/bin/sh # # Uncomment this if you want some logging #echo $@ >> /tmp/idmap.sh.log if [ "$1" == "SIDTOID" ] then # Note. The number returned has to be within the range defined #echo "Sending UID:1000005" >> /tmp/idmap.sh.log echo "UID:1000005" exit 0 else #echo "Sending ERR: No idea what to do" >> /tmp/idmap.sh.log echo "ERR: No idea what to do" exit 1 fi
Clearly, this script is not enough, as it should probably use wbinfo to determine if an incoming SID is a user or group SID and then look up the mapping in a table or use some other mechanism for mapping SIDs to UIDs and etc.
Please be aware that the script is called with the
_NO_WINBINDD environment variable set to 1. This prevents
recursive calls into winbind from the script both via
explicit calls to wbinfo and via implicit calls via
nss_winbind. For example a call to
could trigger such an infinite recursion.
It is safe to call
wbinfo -n and
wbinfo -s from within an idmap script. To
do so, the script must unset the _NO_WINBINDD environment
variable right before the call to
and set it to 1 again right after
has returned to protect against the recursion.