.\"
.\" Copyright (c) 2010-2015 Todd C. Miller <Todd.Miller@courtesan.com>
.\"
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.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
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.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\" ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.Dd November 20, 2015
.Dt SUDO 5
.Os Sudo 1.8.16
.Sh NAME
.Nm sudo.conf
.Nd configuration for sudo front end
.Sh DESCRIPTION
The
.Nm sudo.conf
file is used to configure the
.Nm sudo
front end.
It specifies the security policy and I/O logging plugins, debug flags
as well as plugin-agnostic path names and settings.
.Pp
The
.Nm
file supports the following directives, described in detail below.
.Bl -tag -width 8n
.It Plugin
a security policy or I/O logging plugin
.It Path
a plugin-agnostic path
.It Set
a front end setting, such as
.Em disable_coredump
or
.Em group_source
.It Debug
debug flags to aid in debugging
.Nm sudo ,
.Nm sudoreplay ,
.Nm visudo ,
and the
.Nm sudoers
plugin.
.El
.Pp
The pound sign
.Pq Ql #
is used to indicate a comment.
Both the comment character and any text after it, up to the end of
the line, are ignored.
.Pp
Long lines can be continued with a backslash
.Pq Ql \e
as the last character on the line.
Note that leading white space is removed from the beginning of lines
even when the continuation character is used.
.Pp
Non-comment lines that don't begin with
.Li Plugin ,
.Li Path ,
.Li Debug ,
or
.Li Set
are silently ignored.
.Pp
The
.Nm
file is always parsed in the
.Dq Li C
locale.
.Ss Plugin configuration
.Nm 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
.Nm sudo
front end.
Plugins are dynamically loaded based on the contents of
.Nm .
.Pp
A
.Li Plugin
line consists of the
.Li Plugin
keyword, followed by the
.Em symbol_name
and the
.Em path
to the dynamic shared object that contains the plugin.
The
.Em symbol_name
is the name of the
.Li struct policy_plugin
or
.Li struct io_plugin
symbol contained in the plugin.
The
.Em path
may be fully qualified or relative.
If not fully qualified, it is relative to the directory
specified by the
.Em plugin_dir
.Li Path
setting, which defaults to
.Pa /usr/lib/sudo .
In other words:
.Bd -literal -offset indent
Plugin sudoers_policy sudoers.so
.Ed
.Pp
is equivalent to:
.Bd -literal -offset indent
Plugin sudoers_policy /usr/lib/sudo/sudoers.so
.Ed
.Pp
If the plugin was compiled statically into the
.Nm sudo
binary instead of being installed as a dynamic shared object, the
.Em path
should be specified without a leading directory,
as it does not actually exist in the file system.
For example:
.Bd -literal -offset indent
Plugin sudoers_policy sudoers.so
.Ed
.Pp
Starting with
.Nm sudo
1.8.5, any additional parameters after the
.Em path
are passed as arguments to the plugin's
.Em open
function.
For example, to override the compile-time default sudoers file mode:
.Bd -literal -offset indent
Plugin sudoers_policy sudoers.so sudoers_mode=0440
.Ed
.Pp
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.
.Pp
If no
.Nm
file is present, or if it contains no
.Li Plugin
lines, the
.Nm 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:
.Bd -literal -offset indent
Plugin sudoers_policy sudoers.so
Plugin sudoers_io sudoers.so
.Ed
.Pp
For more information on the
.Nm sudo
plugin architecture, see the
.Xr sudo_plugin 8
manual.
.Ss Path settings
A
.Li Path
line consists of the
.Li Path
keyword, followed by the name of the path to set and its value.
For example:
.Bd -literal -offset indent
Path noexec /usr/lib/sudo/sudo_noexec.so
Path askpass /usr/X11R6/bin/ssh-askpass
.Ed
.Pp
If no path name is specified, features relying on the specified
setting will be disabled.
Disabling
.Li Path
settings is only supported in
.Nm sudo
version 1.8.16 and higher.
.Pp
The following plugin-agnostic paths may be set in the
.Pa /etc/sudo.conf
file:
.Bl -tag -width 8n
.It 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
.Nm sudo
is executed from a graphical (as opposed to text-based) application.
The program specified by
.Em askpass
should display the argument passed to it as the prompt and write
the user's password to the standard output.
The value of
.Em askpass
may be overridden by the
.Ev SUDO_ASKPASS
environment variable.
.It noexec
The fully-qualified path to a shared library containing dummy
versions of the
.Fn execl ,
.Fn execle ,
.Fn execlp ,
.Fn exect ,
.Fn execv ,
.Fn execve ,
.Fn execvP ,
.Fn execvp ,
.Fn execvpe ,
.Fn fexecve ,
.Fn popen ,
.Fn posix_spawn ,
.Fn posix_spawnp ,
and
.Fn system
library functions that just return an error.
This is used to implement the
.Em noexec
functionality on systems that support
.Ev LD_PRELOAD
or its equivalent.
The default value is:
.Pa /usr/lib/sudo/sudo_noexec.so .
.It plugin_dir
The default directory to use when searching for plugins
that are specified without a fully qualified path name.
The default value is
.Pa /usr/lib/sudo .
.It sesh
The fully-qualified path to the
.Nm sesh
binary.
This setting is only used when
.Nm sudo
is built with SELinux support.
The default value is
.Pa /usr/lib/sudo/sesh .
.El
.Ss Other settings
The
.Nm
file also supports the following front end settings:
.Bl -tag -width 8n
.It disable_coredump
Core dumps of
.Nm sudo
itself are disabled by default to prevent the disclosure of potentially
sensitive information.
To aid in debugging
.Nm sudo
crashes, you may wish to re-enable core dumps by setting
.Dq disable_coredump
to false in
.Nm
as follows:
.Bd -literal -offset indent
Set disable_coredump false
.Ed
.Pp
All modern operating systems place restrictions on core dumps
from setuid processes like
.Nm sudo
so this option can be enabled without compromising security.
To actually get a
.Nm sudo
core file you will likely need to enable core dumps for setuid processes.
On BSD and Linux systems this is accomplished in the
.Xr sysctl
command.
On Solaris, the
.Xr coreadm
command is used to configure core dump behavior.
.Pp
This setting is only available in
.Nm sudo
version 1.8.4 and higher.
.It group_source
.Nm 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
.Xr getconf 1
utility, running:
.Dl getconf NGROUPS_MAX
will return the maximum number of groups.
.Pp
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
.Nm sudo
version 1.8.7, if the user's kernel group list has the maximum number
of entries,
.Nm 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.
.Pp
The
.Em group_source
setting allows the administrator to change this default behavior.
Supported values for
.Em group_source
are:
.Bl -tag -width 8n
.It 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
.Dq 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
.Nm sudo
1.8.7.
.It dynamic
Always query the group database directly.
It is
.Dq 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,
.Nm sudo
supports efficient group queries on AIX, BSD, HP-UX, Linux and
Solaris.
.It 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
.Nm sudo
1.8.7 and higher.
.El
.Pp
For example, to cause
.Nm sudo
to only use the kernel's static list of groups for the user:
.Bd -literal -offset indent
Set group_source static
.Ed
.Pp
This setting is only available in
.Nm sudo
version 1.8.7 and higher.
.It 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,
.Nm 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.
.Pp
This setting is only available in
.Nm sudo
version 1.8.7 and higher.
.It probe_interfaces
By default,
.Nm 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:
.Bd -literal -offset indent
Set probe_interfaces false
.Ed
.Pp
This setting is only available in
.Nm sudo
version 1.8.10 and higher.
.El
.Ss Debug flags
.Nm sudo
versions 1.8.4 and higher support a flexible debugging framework
that can help track down what
.Nm sudo
is doing internally if there is a problem.
.Pp
A
.Li Debug
line consists of the
.Li Debug
keyword, followed by the name of the program (or plugin) to debug
.Pq Nm sudo , Nm visudo , Nm sudoreplay , Nm sudoers ,
the debug file name and a comma-separated list of debug flags.  The
debug flag syntax used by
.Nm sudo
and the
.Nm sudoers
plugin is
.Em subsystem Ns @ Ns Em priority
but a plugin is free to use a different format so long as it does
not include a comma
.Pq Ql \&, .
.Pp
For example:
.Bd -literal -offset indent
Debug sudo /var/log/sudo_debug all@warn,plugin@info
.Ed
.Pp
would log all debugging statements at the
.Em warn
level and higher in addition to those at the
.Em info
level for the plugin subsystem.
.Pp
As of
.Nm sudo
1.8.12, multiple
.Li Debug
entries may be specified per program.
Older versions of
.Nm sudo
only support a single
.Li Debug
entry per program.
Plugin-specific
.Li Debug
entries are also supported starting with
.Nm sudo
1.8.12 and are matched by either the base name of the plugin that was loaded
(for example
.Li sudoers.so )
or by the plugin's fully-qualified path name.
Previously, the
.Nm sudoers
plugin shared the same
.Li Debug
entry as the
.Nm sudo
front end and could not be configured separately.
.Pp
The following priorities are supported, in order of decreasing severity:
.Em crit , err , warn , notice , diag , info , trace
and
.Em debug .
Each priority, when specified, also includes all priorities higher
than it.  For example, a priority of
.Em notice
would include debug messages logged at
.Em notice
and higher.
.Pp
The priorities
.Em trace
and
.Em 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:
.Bd -literal -offset indent
sudo[123] -> get_user_groups @ src/sudo.c:385
sudo[123] <- get_user_groups @ src/sudo.c:429 := groups=10,0,5
.Ed
.Pp
When the function is entered, indicated by a right arrow
.Ql -> ,
the program, process ID, function, source file and line number
are logged.
When the function returns, indicated by a left arrow
.Ql <- ,
the same information is logged along with the return value.
In this case, the return value is a string.
.Pp
The following subsystems are used by the
.Nm sudo
front-end:
.Bl -tag -width Fl
.It Em all
matches every subsystem
.It Em args
command line argument processing
.It Em conv
user conversation
.It Em edit
sudoedit
.It Em event
event subsystem
.It Em exec
command execution
.It Em main
.Nm sudo
main function
.It Em netif
network interface handling
.It Em pcomm
communication with the plugin
.It Em plugin
plugin configuration
.It Em pty
pseudo-tty related code
.It Em selinux
SELinux-specific handling
.It Em util
utility functions
.It Em utmp
utmp handling
.El
.Pp
The
.Xr sudoers 5
plugin includes support for additional subsystems.
.Sh FILES
.Bl -tag -width 24n
.It Pa /etc/sudo.conf
.Nm sudo
front end configuration
.El
.Sh EXAMPLES
.Bd -literal
#
# Default /etc/sudo.conf file
#
# Format:
#   Plugin plugin_name plugin_path plugin_options ...
#   Path askpass /path/to/askpass
#   Path noexec /path/to/sudo_noexec.so
#   Debug sudo /var/log/sudo_debug all@warn
#   Set disable_coredump true
#
# The plugin_path is relative to /usr/lib/sudo unless
#   fully qualified.
# The plugin_name corresponds to a global symbol in the plugin
#   that contains the plugin interface structure.
# The plugin_options are optional.
#
# The sudoers plugin is used by default if no Plugin lines are
# present.
Plugin sudoers_policy sudoers.so
Plugin sudoers_io sudoers.so

#
# Sudo askpass:
#
# An askpass helper program may be specified to provide a graphical
# password prompt for "sudo -A" support.  Sudo does not ship with
# its own askpass program but can use the OpenSSH askpass.
#
# Use the OpenSSH askpass
#Path askpass /usr/X11R6/bin/ssh-askpass
#
# Use the Gnome OpenSSH askpass
#Path askpass /usr/libexec/openssh/gnome-ssh-askpass

#
# Sudo noexec:
#
# Path to a shared library containing dummy versions of the execv(),
# execve() and fexecve() library functions that just return an error.
# This is used to implement the "noexec" functionality on systems that
# support C<LD_PRELOAD> or its equivalent.
# The compiled-in value is usually sufficient and should only be
# changed if you rename or move the sudo_noexec.so file.
#
#Path noexec /usr/lib/sudo/sudo_noexec.so

#
# Core dumps:
#
# By default, sudo disables core dumps while it is executing
# (they are re-enabled for the command that is run).
# To aid in debugging sudo problems, you may wish to enable core
# dumps by setting "disable_coredump" to false.
#
#Set disable_coredump false

#
# User groups:
#
# Sudo passes the user's group list to the policy plugin.
# If the user is a member of the maximum number of groups (usually 16),
# sudo will query the group database directly to be sure to include
# the full list of groups.
#
# On some systems, this can be expensive so the behavior is configurable.
# The "group_source" setting has three possible values:
#   static   - use the user's list of groups returned by the kernel.
#   dynamic  - query the group database to find the list of groups.
#   adaptive - if user is in less than the maximum number of groups.
#              use the kernel list, else query the group database.
#
#Set group_source static
.Ed
.Sh SEE ALSO
.Xr sudoers 5 ,
.Xr sudo 8 ,
.Xr sudo_plugin 8
.Sh HISTORY
See the HISTORY file in the
.Nm sudo
distribution (https://www.sudo.ws/history.html) for a brief
history of sudo.
.Sh AUTHORS
Many people have worked on
.Nm sudo
over the years; this version consists of code written primarily by:
.Bd -ragged -offset indent
.An Todd C. Miller
.Ed
.Pp
See the CONTRIBUTORS file in the
.Nm sudo
distribution (https://www.sudo.ws/contributors.html) for an
exhaustive list of people who have contributed to
.Nm sudo .
.Sh BUGS
If you feel you have found a bug in
.Nm sudo ,
please submit a bug report at https://bugzilla.sudo.ws/
.Sh SUPPORT
Limited free support is available via the sudo-users mailing list,
see https://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or
search the archives.
.Sh DISCLAIMER
.Nm sudo
is provided
.Dq AS IS
and any express or implied warranties, including, but not limited
to, the implied warranties of merchantability and fitness for a
particular purpose are disclaimed.
See the LICENSE file distributed with
.Nm sudo
or https://www.sudo.ws/license.html for complete details.
