getgroups() reads through all group sources

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Environment

SUSE Linux Enterprise Server 10 SP1
SUSE Linux Enterprise Server 10

Situation

/etc/nsswitch.conf has been modified to get group information from more than one source, for example:

group: files [SUCCESS=return] ldap

However, despite the group of a user requested exists in /etc/group, the other source (LDAP, in this case) gets requested as well. This could lead to programs like id, which call getgroups(2), hang for quite a while if the LDAP server isn't ready, or programs that execute initgroups(3) to not start up correctly (for example, OpenLDAP itself.)

Resolution

Use [!NOTFOUND=return] instead of [SUCCESS=return] to stop accessing the following modules.

Additional Information

When looking for additional group ownership of a user, a SUCCESS status of a libnss_* module would stop the search as soon as one group is found in that module. However, additional groups may be present in the other modules, thus the module returns a different (undocumented) return code instead ofSUCCESSin this case. The negated NOTFOUND catches this reliably. Please note that all groups of a user must be specified completely in one of the sources, not spreaded among them, otherwise the user would have incomplete group ownerships.

Disclaimer

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