Plugin configuration¶

sudo supports a plugin architecture for security policies and input/output logging. Third parties can develop and distribute their own policy and I/O logging plugins to work seamlessly with the sudo front end. Plugins are dynamically loaded based on the contents of sudo.conf.

A Plugin line consists of the Plugin keyword, followed by the symbol_name and the path to the dynamic shared object that contains the plugin. The symbol_name is the name of the struct policy_plugin or struct io_plugin symbol contained in the plugin. The path may be fully qualified or relative. If not fully qualified, it is relative to the directory specified by the plugin_dir Path setting, which defaults to /usr/libexec/sudo. In other words:

Plugin sudoers_policy sudoers.so

is equivalent to:

Plugin sudoers_policy /usr/libexec/sudo/sudoers.so

If the plugin was compiled statically into the sudo binary instead of being installed as a dynamic shared object, the path should be specified without a leading directory, as it does not actually exist in the file system. For example:

Plugin sudoers_policy sudoers.so

Starting with sudo 1.8.5, any additional parameters after the path are passed as arguments to the plugin's open function. For example, to override the compile-time default sudoers file mode:

Plugin sudoers_policy sudoers.so sudoers_mode=0440

See the sudoers(5) manual for a list of supported arguments.

The same dynamic shared object may contain multiple plugins, each with a different symbol name. The file must be owned by uid 0 and only writable by its owner. Because of ambiguities that arise from composite policies, only a single policy plugin may be specified. This limitation does not apply to I/O plugins.

If no sudo.conf file is present, or if it contains no Plugin lines, the sudoers plugin will be used as the default security policy and for I/O logging (if enabled by the policy). This is equivalent to the following:

Plugin sudoers_policy sudoers.so
Plugin sudoers_io sudoers.so

For more information on the sudo plugin architecture, see the sudo_plugin(5) manual.

Path settings¶

A Path line consists of the Path keyword, followed by the name of the path to set and its value. For example:

Path noexec /usr/libexec/sudo/sudo_noexec.so
Path askpass /usr/X11R6/bin/ssh-askpass

If no path name is specified, features relying on the specified setting will be disabled. Disabling Path settings is only supported in sudo version 1.8.16 and higher.

The following plugin-agnostic paths may be set in the /etc/sudo.conf file:

askpass

The fully qualified path to a helper program used to read the user's password when no terminal is available. This may be the case when sudo is executed from a graphical (as opposed to text-based) application. The program specified by askpass should display the argument passed to it as the prompt and write the user's password to the standard output. The value of askpass may be overridden by the SUDO_ASKPASS environment variable.

devsearch

An ordered, colon-separated search path of directories to look in for device nodes. This is used when mapping the process's tty device number to a device name on systems that do not provide such a mechanism. Sudo will not recurse into sub-directories. If terminal devices may be located in a sub-directory of /dev, that path must be explicitly listed in devsearch. The default value is: /dev/pts:/dev/vt:/dev/term:/dev/zcons:/dev/pty:/dev

This option is ignored on systems that support either the devname() or _ttyname_dev() functions, for example BSD, macOS and Solaris.

noexec

The fully-qualified path to a shared library containing wrappers for the execl(), execle(), execlp(), exect(), execv(), execve(), execvP(), execvp(), execvpe(), fexecve(), popen(), posix_spawn(), posix_spawnp(), system(), and wordexp() library functions that prevent the execution of further commands. This is used to implement the noexec functionality on systems that support LD_PRELOAD or its equivalent. The default value is: /usr/libexec/sudo/sudo_noexec.so.

plugin_dir

The default directory to use when searching for plugins that are specified without a fully qualified path name. The default value is /usr/libexec/sudo.

sesh

The fully-qualified path to the sesh binary. This setting is only used when sudo is built with SELinux support. The default value is /usr/libexec/sudo/sesh.

Other settings¶

The sudo.conf file also supports the following front end settings:

disable_coredump

Core dumps of sudo itself are disabled by default to prevent the disclosure of potentially sensitive information. To aid in debugging sudo crashes, you may wish to re-enable core dumps by setting “disable_coredump” to false in sudo.conf as follows:

Set disable_coredump false

All modern operating systems place restrictions on core dumps from setuid processes like sudo so this option can be enabled without compromising security. To actually get a sudo core file you will likely need to enable core dumps for setuid processes. On BSD and Linux systems this is accomplished in the sysctl command. On Solaris, the coreadm command is used to configure core dump behavior.

This setting is only available in sudo version 1.8.4 and higher.

group_source

sudo passes the invoking user's group list to the policy and I/O plugins. On most systems, there is an upper limit to the number of groups that a user may belong to simultaneously (typically 16 for compatibility with NFS). On systems with the getconf(1) utility, running:

getconf NGROUPS_MAX

will return the maximum number of groups.

However, it is still possible to be a member of a larger number of groups--they simply won't be included in the group list returned by the kernel for the user. Starting with sudo version 1.8.7, if the user's kernel group list has the maximum number of entries, sudo will consult the group database directly to determine the group list. This makes it possible for the security policy to perform matching by group name even when the user is a member of more than the maximum number of groups.

The group_source setting allows the administrator to change this default behavior. Supported values for group_source are:

static

Use the static group list that the kernel returns. Retrieving the group list this way is very fast but it is subject to an upper limit as described above. It is “static” in that it does not reflect changes to the group database made after the user logs in. This was the default behavior prior to sudo 1.8.7.

dynamic

Always query the group database directly. It is “dynamic” in that changes made to the group database after the user logs in will be reflected in the group list. On some systems, querying the group database for all of a user's groups can be time consuming when querying a network-based group database. Most operating systems provide an efficient method of performing such queries. Currently, sudo supports efficient group queries on AIX, BSD, HP-UX, Linux and Solaris.

adaptive

Only query the group database if the static group list returned by the kernel has the maximum number of entries. This is the default behavior in sudo 1.8.7 and higher.

For example, to cause sudo to only use the kernel's static list of groups for the user:

Set group_source static

This setting is only available in sudo version 1.8.7 and higher.

max_groups

The maximum number of user groups to retrieve from the group database. Values less than one will be ignored. This setting is only used when querying the group database directly. It is intended to be used on systems where it is not possible to detect when the array to be populated with group entries is not sufficiently large. By default, sudo will allocate four times the system's maximum number of groups (see above) and retry with double that number if the group database query fails. However, some systems just return as many entries as will fit and do not indicate an error when there is a lack of space.

This setting is only available in sudo version 1.8.7 and higher.

probe_interfaces

By default, sudo will probe the system's network interfaces and pass the IP address of each enabled interface to the policy plugin. This makes it possible for the plugin to match rules based on the IP address without having to query DNS. On Linux systems with a large number of virtual interfaces, this may take a non-negligible amount of time. If IP-based matching is not required, network interface probing can be disabled as follows:

Set probe_interfaces false

This setting is only available in sudo version 1.8.10 and higher.

Debug flags¶

sudo versions 1.8.4 and higher support a flexible debugging framework that can help track down what sudo is doing internally if there is a problem.

A Debug line consists of the Debug keyword, followed by the name of the program (or plugin) to debug (sudo, visudo, sudoreplay, sudoers), the debug file name and a comma-separated list of debug flags. The debug flag syntax used by sudo and the sudoers plugin is subsystem@priority but a plugin is free to use a different format so long as it does not include a comma (‘,’).

For example:

Debug sudo /var/log/sudo_debug all@warn,plugin@info

would log all debugging statements at the warn level and higher in addition to those at the info level for the plugin subsystem.

As of sudo 1.8.12, multiple Debug entries may be specified per program. Older versions of sudo only support a single Debug entry per program. Plugin-specific Debug entries are also supported starting with sudo 1.8.12 and are matched by either the base name of the plugin that was loaded (for example sudoers.so) or by the plugin's fully-qualified path name. Previously, the sudoers plugin shared the same Debug entry as the sudo front end and could not be configured separately.

The following priorities are supported, in order of decreasing severity: crit, err, warn, notice, diag, info, trace and debug. Each priority, when specified, also includes all priorities higher than it. For example, a priority of notice would include debug messages logged at notice and higher.

The priorities trace and debug also include function call tracing which logs when a function is entered and when it returns. For example, the following trace is for the get_user_groups() function located in src/sudo.c:

sudo[123] -> get_user_groups @ src/sudo.c:385
sudo[123] <- get_user_groups @ src/sudo.c:429 := groups=10,0,5

When the function is entered, indicated by a right arrow ‘->’, the program, process ID, function, source file and line number are logged. When the function returns, indicated by a left arrow ‘<-’, the same information is logged along with the return value. In this case, the return value is a string.

The following subsystems are used by the sudo front-end:

all

matches every subsystem

args

command line argument processing

conv

user conversation

edit

sudoedit

event

event subsystem

exec

command execution

main

sudo main function

netif

network interface handling

pcomm

communication with the plugin

plugin

plugin configuration

pty

pseudo-tty related code

selinux

SELinux-specific handling

util

utility functions

utmp

utmp handling

The sudoers(5) plugin includes support for additional subsystems.