Identification ensures that a user is who he or she claims to be (for example, a unique username). Authentication proves the identity of the user (for example, with a password or keys).
Systems that need authentication must use a configurable standard library developed for this purpose, such as a pluggable authentication module (PAM).
A PAM environment consists of the following components:
PAM provides a framework for you to use within a system; for example, if you use username and password to authenticate users, you can use PAM to prompt for those credentials.
PAM simplifies the task of choosing which algorithm or database to use for authentication. To configure a system that has been configured to use PAM (and make use of the PAM framework), you edit a text file to specify what PAM needs to do.
The framework also simplifies the task of changing which algorithm or database to use. By editing the PAM configuration file to change which shared object file the PAM library invokes, you can change how your system authenticates users without changing its code.
The OpenPAM framework is integrated with QNX Neutrino to support authentication and identification for the QNX Neutrino utilities that use it.
The login utility is one example of a QNX Neutrino utility that is PAM-aware and supported by the PAM framework. Under the PAM framework, the login command is dependent on the PAM library and loads libpam.so. The PAM library, in turn, opens the PAM modules explicitly referenced in the PAM configuration file.
PAM modules (pam_*.so) are usually located in one or more of the following directories, but they can be kept elsewhere:
If you plan to keep the PAM modules in a different directory, use the confstr value _CS_PAMLIB to override the default search paths and indicate where to find them. If you override the default directories, you must specify a single path. Multiple search paths are not permitted.
setconf _CS_PAMLIB /system/lib/pamEnsure that the permissions of the PAM module paths and the module files themselves exclude write (w) permission for group and other.
Without the PAM framework in place, a login sequence typically checks /etc/passwd (and checks the shadow file /etc/shadow, if a password is set) to get a user entry and set credentials.
PAM configuration files are usually located in one or more of the following directories, but they may instead be kept elsewhere:
If you plan to keep the PAM configuration files in a different directory, use the confstr value _CS_PAMCONF to override the default search paths and indicate where to find them. If you are overriding the default directories, you must specify a single path; multiple search paths are not permitted.
setconf _CS_PAMCONF /system/etc/pam.d
The directory may contain multiple PAM configuration files to support a range of security policies beyond authentication. For example, the login service would look for the configuration file /etc/pam.d/login or /usr/local/etc/pam.d/login if the default paths are used.
If no filename matches the service name (binary name) that the application registered, the service looks instead for a file named other in the search paths for the PAM configuration files.
Configuration commands are stacked in the PAM configuration file to create a chain. They are processed in top-down order by libpam. The configuration file specifies facilities, control flags, modules (shared object files) and optional arguments using the following syntax:
facility control_flag module arguments
For example:
auth required pam_qnx.so auth required pam_radius.so account required pam_permit.so
You specify the facility with one of the following values:
Facility | Task | Functions |
---|---|---|
account | Account management | pam_acct_mgmt |
password | Password management | pam_chauthtok |
auth | Authentication | pam_authenticate and pam_setcred |
session | Session management | pam_open_session and pam_close_session |
The control flags describe what happens if a function of the indicated type succeeds or fails. The PAM facilities each support the following control flags:
Flag | Purpose |
---|---|
binding | If the module fails and is part of a chain, the chain executes and the request is denied. Success breaks the chain. |
required | If the module fails and is part of a chain, the chain executes and the request is denied. Success does not break the chain. |
requisite | If the module fails and is part of a chain, the chain is broken. Success does not break the chain. |
sufficient | Failure does not break the chain. If the module succeeds with no prior failures in the chain, the chain is broken. |
optional | The result is ignored. |
For example:
auth sufficient pam_rootok.so auth optional pam_motd.so nullok auth requisite pam_qnx.so nullok
or
password requisite pam_qnx.so nullok account requisite pam_qnx.so nullok
QNX Neutrino supports the following modules:
Module | Description | Example |
---|---|---|
pam_deny.so | Always returns failure. |
Permit all logins but deny any attempts to change a password: /etc/pam.d/passwd: auth requisite pam_permit.so account requisite pam_permit.so session requisite pam_permit.so password requisite pam_deny.so |
pam_echo.so | Displays a message. Fails if the message file does not exist. |
Print a message from a file: /etc/pam.d/passwd: password optional pam_echo.so file=/path/good-password.txt |
pam_exec.so | Runs a command. Fails if the command does not run. |
Runs a command after each local password change: /etc/pam.d/passwd: password optional pam_exec.so /path/command |
pam_mac.so | Determines the type that should be associated with the user and switches to it if a security policy is loaded. | Configure PAM for ssh, making use of the
allow_mac_policy option (to avoid having to change any
configuration based on whether a security policy is used or not):
auth requisite pam_qnx.so account requisite pam_qnx.so session requisite pam_qnx.so session requisite pam_mac.so allow_no_policy password requisite pam_qnx.so |
pam_permit.so | Always returns success. | Log in as any user without being prompted for a password:
/etc/pam.d/login: auth requisite pam_permit.so account requisite pam_permit.so session requisite pam_permit.so password requisite pam_permit.so |
pam_qnx.so | Behavior is comparable to previous QNX versions. | Provide legacy behavior:
/etc/pam.d/login: auth requisite pam_qnx.so nullok account requisite pam_qnx.so nullok session requisite pam_qnx.so nullok password requisite pam_qnx.so nullok |
pam_radius.so | Authenticate on RADIUS protocol. | Authenticate the SSH server request from the RADIUS
server:
/etc/pam.d/sshd: auth sufficient pam_radius.so |
pam_rootok.so | Always returns success for the superuser. | Check for UID 0:
auth sufficient pam_rootok.so |
pam_self.so | Returns success if the target user's UID matches the current UID. | Self authentication:
auth requisite pam_self.so |
pam_ftpusers.so | Returns success if the user is listed in /etc/ftpusers. | Account management:
account required pam_ftpusers.so |
pam_group.so | Accepts or rejects users based on their membership in a particular group. | Permit only members of the admin group to login:
auth requisite pam_group.so account required pam_group.so group=admin |
The following QNX Neutrino utilities are PAM-aware and supported by the PAM framework:
The following pseudocode provides an example of how to integrate PAM functions into your system:
pam_start("service name", ...) if returns -1 go to "no PAM") otherwise: auth acctmgmt chauthtok setcred opensession ... closesession pam_end
The following code provides an example of how to integrate PAM functions into your system for login:
# apply additional groups as specified in groups.conf auth optional pam_group.so # use standard un*x validation, allow blank passwords auth required pam_qnx.so nullok # deny on failure auth requisite pam_deny.so password required pam_qnx.so nullok password requisite pam_deny.so account required pam_qnx.so nullok account requisite pam_deny.so session required pam_qnx.so nullok session requisite pam_deny.so
The following code provides an example of how to integrate PAM functions into your system for su:
# root can su with no auth auth sufficient pam_rootok.so # use standard un*x validation, allow blank passwords auth required pam_qnx.so nullok # deny on failure auth requisite pam_deny.so account required pam_qnx.so nullok account requisite pam_deny.so session required pam_qnx.so nullok session requisite pam_deny.so # no password facility
Since OpenPAM and the PAM modules use syslogd to log errors, you can use the following steps to use syslogd for debugging:
*.* /dev/slog
Now you should be able to see PAM error messages using slog2info.
Use this section to troubleshoot your PAM configuration.
Invalid password database
To troubleshoot an invalid password database, check:
A valid set up looks like this:
File | User | Group | Permissions |
---|---|---|---|
/etc/passwd | root | root | 0644 |
/etc/shadow | root | root | 0600 |
/etc/group | root | root | 0644 |
The following commands may help you find the information you need to change:
ls -ld /etc/passwd ls -ld /etc/shadow ls -ld /etc/group cat /etc/passwd cat /etc/shadow cat /etc/group
Incorrect permissions or ownership of utilities
To troubleshoot incorrect permissions or ownership of utilities, check that:
A valid set up looks like this:
Utility | User | Group | Permissions |
---|---|---|---|
login | root | root | 4755 |
passwd | root | root | 4755 |
su | root | root | 4755 |
sshd | root | root | 0755 |
The following commands may help you find the information that you need to change:
ls -ld /etc ls -ld /etc/pam.d ls -l /etc/pam.d ls -ld /etc/pam.d/login ls -ld /etc/pam.d/passwd ls -ld /etc/pam.d/su ls -ld /etc/pam.d/sshd ls -ld /etc/pam.d/ftpd ls -ld /etc/pam.d/sshd ls -ld /etc/pam.d/racoon grep auth /etc/pam.d/* grep password /etc/pam.d/* grep account /etc/pam.d/* grep session /etc/pam.d/*
Incorrect PAM configuration files
To troubleshoot incorrect PAM configuration files, check that:
A valid set up looks like this:
Filepath | User | Group | Permissions |
---|---|---|---|
/etc | root | root | 0755 |
/etc/pam.d | root | root | 0755 |
/etc/pam.d/* | root | root | 0644 |
The following commands may help you find the information you need to change:
ls -ld /etc ls -ld /etc/pam.d ls -l /etc/pam.d ls -ld /etc/pam.d/login ls -ld /etc/pam.d/passwd ls -ld /etc/pam.d/su ls -ld /etc/pam.d/sshd ls -ld /etc/pam.d/ftpd ls -ld /etc/pam.d/sshd ls -ld /etc/pam.d/racoon grep auth /etc/pam.d/* grep password /etc/pam.d/* grep account /etc/pam.d/* grep session /etc/pam.d/*
Missing PAM modules
To troubleshoot missing PAM modules, check that:
Directory or module | User | Group | Permissions |
---|---|---|---|
/user | root | root | 755 |
/user/lib | root | root | 755 |
/user/lib/pam_*.so.2 | root | root | 755 |
The following commands may help you find which modules are missing and determine which directory permissions need to change:
ls -ld /usr ls -ld /usr/lib ls -ld /usr/lib/pam_deny.so ls -ld /usr/lib/pam_echo.so ls -ld /usr/lib/pam_exec.so ls -ld /usr/lib/pam_ftpusers.so ls -ld /usr/lib/pam_group.so ls -ld /usr/lib/pam_permit.so ls -ld /usr/lib/pam_qnx.so ls -ld /usr/lib/pam_radius.so ls -ld /usr/lib/pam_rootok.so ls -ld /usr/lib/pam_self.so