Known annotations

The org.freedesktop.policykit.exec.path annotation is used by the pkexec program shipped with polkit - see the pkexec(1) man page for details.

The org.freedesktop.policykit.imply annotation (its value is a string containing a space-separated list of action identifiers) can be used to define meta actions. The way it works is that if a subject is authorized for an action with this annotation, then it is also authorized for any action specified by the annotation. A typical use of this annotation is when defining an UI shell with a single lock button that should unlock multiple actions from distinct mechanisms.

The org.freedesktop.policykit.owner annotation can be used to define a set of users who can query whether a client is authorized to perform this action. If this annotation is not specified, then only root can query whether a client running as a different user is authorized for an action. The value of this annotation is a string containing a space-separated list of PolkitIdentity entries, for example "unix-user:42 unix-user:colord". A typical use of this annotation is for a daemon process that runs as a system user rather than root.

The Polkit type

The following methods are available on the polkit object:

void addRule(polkit.Result function(action, subject) {...});

void addAdminRule(string[] function(action, subject) {...});

void log(string message);

string spawn(string[] argv);

The addRule() method is used for adding a function that may be called whenever an authorization check for action and subject is performed. Functions are called in the order they have been added until one of the functions returns a value. Hence, to add an authorization rule that is processed before other rules, put it in a file in /etc/polkit-1/rules.d with a name that sorts before other rules files, for example 00-early-checks.rules. Each function should return a value from polkit.Result

polkit.Result = {
    NO              : "no",
    YES             : "yes",
    AUTH_SELF       : "auth_self",
    AUTH_SELF_KEEP  : "auth_self_keep",
    AUTH_ADMIN      : "auth_admin",
    AUTH_ADMIN_KEEP : "auth_admin_keep",
    NOT_HANDLED     : null
};

corresponding to the values that can be used as defaults. If the function returns polkit.Result.NOT_HANDLED, null, undefined or does not return a value at all, the next user function is tried.

Keep in mind that if polkit.Result.AUTH_SELF_KEEP or polkit.Result.AUTH_ADMIN_KEEP is returned, authorization checks for the same action identifier and subject will succeed (that is, return polkit.Result.YES) for the next brief period (e.g. five minutes) even if the variables passed along with the check are different. Therefore, if the result of an authorization rule depend on such variables, it should not use the "*_KEEP" constants (if similar functionality is required, the authorization rule can easily implement temporary authorizations using the Date[9] type for timestamps).

The addAdminRule() method is used for adding a function that may be called whenever administrator authentication is required. The function is used to specify what identities may be used for administrator authentication for the authorization check identified by action and subject. Functions added are called in the order they have been added until one of the functions returns a value. Each function should return an array of strings where each string is of the form "unix-group:<group>", "unix-netgroup:<netgroup>" or "unix-user:<user>". If the function returns null, undefined or does not return a value at all, the next function is tried.

There is no guarantee that a function registered with addRule() or addAdminRule() is ever called - for example an early rules file could register a function that always returns a value, hence ensuring that functions added later are never called.

If user-provided code takes a long time to execute, an exception will be thrown which normally results in the function being terminated (the current limit is 15 seconds). This is used to catch runaway scripts. If the duktape JavaScript backend is compiled in, instead of mozjs, no exception will be thrown—the script will be killed right away (same timeout).

The spawn() method spawns an external helper identified by the argument vector argv and waits for it to terminate. If an error occurs or the helper doesn't exit normally with exit code 0, an exception is thrown. If the helper does not exit within 10 seconds, it is killed. Otherwise, the program's standard output is returned as a string. The spawn() method should be used sparingly as helpers may take a very long or indeterminate amount of time to complete and no other authorization check can be handled while the helper is running. Note that the spawned programs will run as the unprivileged polkitd system user.

The log() method writes the given message to the system logger prefixed with the JavaScript filename and line number. Log entries are emitted using the LOG_AUTHPRIV flag meaning that the log entries usually ends up in the file /var/log/secure. The log() method is usually only used when debugging rules. The Action and Subject types has suitable toString() methods defined for easy logging, for example,

polkit.addRule(function(action, subject) {
    if (action.id == "org.freedesktop.policykit.exec") {
        polkit.log("action=" + action);
        polkit.log("subject=" + subject);
    }
});

will produce the following when the user runs 'pkexec -u bateman bash -i' from a shell:

May 24 14:28:50 thinkpad polkitd[32217]: /etc/polkit-1/rules.d/10-test.rules:3: action=[Action id='org.freedesktop.policykit.exec' command_line='/usr/bin/bash -i' program='/usr/bin/bash' user='bateman' user.gecos='Patrick Bateman' user.display='Patrick Bateman (bateman)']
May 24 14:28:50 thinkpad polkitd[32217]: /etc/polkit-1/rules.d/10-test.rules:4: subject=[Subject pid=1352 user='davidz' groups=davidz,wheel, seat='seat0' session='1' local=true active=true]

The Action type

The action parameter passed to user functions is an object with information about the action being checked. It is of type Action and has the following attribute:

string id

The following methods are available on the Action type:

string lookup(string key);

The lookup() method is used to lookup the polkit variables passed from the mechanism. For example, the pkexec(1) mechanism sets the variable program which can be obtained in JavaScript using the expression action.lookup("program"). If there is no value for the given key, then undefined is returned.

Consult the documentation for each mechanism for what variables are available for each action.

The Subject type

The subject parameter passed to user functions is an object with information about the process being checked. It is of type Subject and has the following attributes

int pid

string user

string[] groups

string seat

string session

string system_unit

boolean local

boolean no_new_privileges

boolean active

The following methods are available on the Subject type:

boolean isInGroup(string groupName);

boolean isInNetGroup(string netGroupName);

The isInGroup() method can be used to check if the subject is in a given group and isInNetGroup() can be used to check if the subject is in a given netgroup.

Authorization Rules Examples

Allow all users in the admin group to perform user administration without changing policy for other users:

polkit.addRule(function(action, subject) {
    if (action.id == "org.freedesktop.accounts.user-administration" &&
        subject.isInGroup("admin")) {
        return polkit.Result.YES;
    }
});

Define administrative users to be the users in the wheel group:

polkit.addAdminRule(function(action, subject) {
    return ["unix-group:wheel"];
});

Forbid users in group children to change hostname configuration (that is, any action with an identifier starting with org.freedesktop.hostname1.) and allow anyone else to do it after authenticating as themselves:

polkit.addRule(function(action, subject) {
    if (action.id.indexOf("org.freedesktop.hostname1.") == 0) {
        if (subject.isInGroup("children")) {
            return polkit.Result.NO;
        } else {
            return polkit.Result.AUTH_SELF_KEEP;
        }
    }
});

Run an external helper to determine if the current user may reboot the system:

polkit.addRule(function(action, subject) {
    if (action.id.indexOf("org.freedesktop.login1.reboot") == 0) {
        try {
            // user-may-reboot exits with success (exit code 0)
            // only if the passed username is authorized
            polkit.spawn(["/opt/company/bin/user-may-reboot",
                          subject.user]);
            return polkit.Result.YES;
        } catch (error) {
            // Nope, but do allow admin authentication
            return polkit.Result.AUTH_ADMIN;
        }
    }
});

The following example shows how the authorization decision can depend on variables passed by the pkexec(1) mechanism:

polkit.addRule(function(action, subject) {
    if (action.id == "org.freedesktop.policykit.exec" &&
        action.lookup("program") == "/usr/bin/cat") {
        return polkit.Result.AUTH_ADMIN;
    }
});

The following example shows another use of variables passed from the mechanism. In this case, the mechanism is UDisks[10] which defines a set of actions and variables[11] that is used to match on:

// Allow users in group 'engineers' to perform any operation on
// some drives without having to authenticate
//
polkit.addRule(function(action, subject) {
    if (action.id.indexOf("org.freedesktop.udisks2.") == 0 &&
        action.lookup("drive.vendor") == "SEAGATE" &&
        action.lookup("drive.model") == "ST3300657SS" &&
        subject.isInGroup("engineers")) {
            return polkit.Result.YES;
        }
    }
});

Allow all processes running as part of the admin.service systemd system unit to perform user administration, as long as they cannot gain new privileges:

polkit.addRule(function(action, subject) {
    if (action.id == "org.freedesktop.accounts.user-administration" &&
        subject.system_unit == "admin.service" &&
        subject.no_new_privileges) {
        return polkit.Result.YES;
    }
});