Description of problem:

The pam_access.so module reads access rules from the access.conf file.

When parsing each whitespace-separated strings in the user/group field in access.conf, pam_access checks for user@host patterns and @netgroup patterns before checking whether the first and last characters are '(' and ')', respectively.

This is an error, for multiple reasons.

First, the access.conf(5) man page states:

> To differentiate user entries from group entries, group entries should be
> written with brackets, e.g.  (group).

This implies that using (group) overrides any other interpretation of the string "group" except a group name, but the behavior of the code does not honor this override.

But more importantly, it makes it IMPOSSIBLE to specify a group that contains an '@' character. E.g.:

+ : (linux-managers@example.org) : ALL

Because the parsing checks for '@' characters before looking for the '(group)' override, the '(linux-managers@example.org)' string is parsed as a user@hostname, instead of as a group:

pam_access(sshd:account): login_access: user=someuser, from=somehost.example.org, file=/etc/security/access.conf
pam_access(sshd:account): line 16: +  :  (linux-managers@example.org)  :  ALL
pam_access(sshd:account): list_match: list= (linux-managers@example.org) , item=someuser
pam_access(sshd:account): user_match: tok=(linux-managers@example.org), item=someuser
pam_access(sshd:account): user_match: tok=(linux-managers, item=someuser
pam_access(sshd:account): string_match: tok=(linux-managers, item=someuser
pam_access(sshd:account): user_match=0, "someuser"

Not being able to use '@' characters in group names breaks sites that are using sssd(8) and use the sss database for user and group lookups. While sites that use only a single domain can leave off the @domain part, in the case where sssd(8) is using multiple domains, users and groups *MUST* be fully-qualified as user@domain and group@domain, respectively, to disambiguate which domain is being referred to.

Fortunately, the fix for this bug is very simple: change the user_match() function in modules/pam_access/pam_access.c to test for the '(group)' construct first, before attempting to split on '@' characters. I'll attach a patch momentarily.

Version-Release number of selected component (if applicable):

pam-1.1.8-12.el7_1.1.x86_64

How reproducible:

On an sssd-enabled system, attempt to grant access via a fully-qualified group@domain entry in /etc/security/access.conf.