Man page "sshd_config" ambiguousness
reuti at staff.uni-marburg.de
Wed Mar 29 22:02:15 AEDT 2017
Defining in "sshd_config" one or more of the possible entries DenyUsers, AllowUsers, DenyGroups, and AllowGroups it turns out, that all of these must be satisfied to grant access. I found many entries on the web clearly stating that it's essentially an intersection of the sets AllowGroups and AlowUsers and not an union. While I can live with this fact when it's the intended behavior, I wonder why the man page explaining these entries was never adjusted. I mean:
$ man sshd_config
[…] The allow/deny directives are processed in the following order: DenyUsers, AllowUsers, DenyGroups, and finally AllowGroups.
For me this always sounded like having an effect one usually find in firewalls: the first matching rule will deny or allow access, and the fall through case must be defined as a special rule.
But it's not the case. While I understand that internal to the `sshd` daemon one must handle one constraint after the other, the behavior for the user (and the user is here is an admin setting it up) is more like:
$ man sshd_config
[…] The allow/deny directives (if present) DenyUsers, AllowUsers, DenyGroups, and AllowGroups will all be checked and a user will be granted access only, if all files permit this. By default a user is permitted to login, unless one or both of the files AllowUsers and AllowGroups is present, where all users not being listed therein are denied access.
I would really like to see an update man page to avoid the confusion which AFAICS many trapped into.
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