Provided by: sudo-ldap_1.9.15p5-3ubuntu5.24.04.1_amd64 
NAME
sudo_logsrv.proto — Sudo log server protocol
DESCRIPTION
Starting with version 1.9.0, sudo supports sending event and I/O logs to a log server. The protocol used
is written in Google's Protocol Buffers domain specific language. The “EXAMPLES” section includes a
complete description of the protocol in Protocol Buffers format.
Because there is no way to determine message boundaries when using Protocol Buffers, the wire size of
each message is sent immediately preceding the message itself as a 32-bit unsigned integer in network
byte order. This is referred to as “length-prefix framing” and is how Google suggests handling the lack
of message delimiters.
The protocol is made up of two basic messages, ClientMessage and ServerMessage, described below. The
server must accept messages up to two megabytes in size. The server may return an error if the client
tries to send a message larger than two megabytes.
Client Messages
A ClientMessage is a container used to encapsulate all the possible message types a client may send to
the server.
message ClientMessage {
oneof type {
AcceptMessage accept_msg = 1;
RejectMessage reject_msg = 2;
ExitMessage exit_msg = 3;
RestartMessage restart_msg = 4;
AlertMessage alert_msg = 5;
IoBuffer ttyin_buf = 6;
IoBuffer ttyout_buf = 7;
IoBuffer stdin_buf = 8;
IoBuffer stdout_buf = 9;
IoBuffer stderr_buf = 10;
ChangeWindowSize winsize_event = 11;
CommandSuspend suspend_event = 12;
ClientHello hello_msg = 13;
}
}
The different ClientMessage sub-messages the client may sent to the server are described below.
TimeSpec
message TimeSpec {
int64 tv_sec = 1;
int32 tv_nsec = 2;
}
A TimeSpec is the equivalent of a POSIX struct timespec, containing seconds and nanoseconds members. The
tv_sec member is a 64-bit integer to support dates after the year 2038.
InfoMessage
message InfoMessage {
message StringList {
repeated string strings = 1;
}
message NumberList {
repeated int64 numbers = 1;
}
string key = 1;
oneof value {
int64 numval = 2;
string strval = 3;
StringList strlistval = 4;
NumberList numlistval = 5;
}
}
An InfoMessage is used to represent information about the invoking user as well as the execution
environment the command runs in the form of key-value pairs. The key is always a string but the value
may be a 64-bit integer, a string, an array of strings, or an array of 64-bit integers. The event log
data is composed of InfoMessage entries. See the “EVENT LOG VARIABLES” section for more information.
ClientHello hello_msg
message ClientHello {
string client_id = 1;
}
A ClientHello message consists of client information that may be sent to the server when the client first
connects.
client_id
A free-form client description. This usually includes the name and version of the client
implementation.
AcceptMessage accept_msg
message AcceptMessage {
TimeSpec submit_time = 1;
repeated InfoMessage info_msgs = 2;
bool expect_iobufs = 3;
}
An AcceptMessage is sent by the client when a command is allowed by the security policy. It contains the
following members:
submit_time
The wall clock time when the command was submitted to the security policy.
info_msgs
An array of InfoMessage describing the user who submitted the command as well as the execution
environment of the command. This information is used to generate an event log entry and may also
be used by server to determine where and how the I/O log is stored.
expect_iobufs
Set to true if the server should expect IoBuffer messages to follow (for I/O logging) or false if
the server should only store the event log.
If an AcceptMessage is sent, the client must not send a RejectMessage or RestartMessage.
RejectMessage reject_msg
message RejectMessage {
TimeSpec submit_time = 1;
string reason = 2;
repeated InfoMessage info_msgs = 3;
}
A RejectMessage is sent by the client when a command is denied by the security policy. It contains the
following members:
submit_time
The wall clock time when the command was submitted to the security policy.
reason The reason the security policy gave for denying the command.
info_msgs
An array of InfoMessage describing the user who submitted the command as well as the execution
environment of the command. This information is used to generate an event log entry.
If a RejectMessage is sent, the client must not send an AcceptMessage or RestartMessage.
ExitMessage exit_msg
message ExitMessage {
TimeSpec run_time = 1;
int32 exit_value = 2;
bool dumped_core = 3;
string signal = 4;
string error = 5;
}
An ExitMessage is sent by the client after the command has exited or has been terminated by a signal. It
contains the following members:
run_time
The total amount of elapsed time since the command started, calculated using a monotonic clock
where possible. This is not the wall clock time.
exit_value
The command's exit value in the range 0-255.
dumped_core
True if the command was terminated by a signal and dumped core.
signal If the command was terminated by a signal, this is set to the name of the signal without the
leading “SIG”. For example, INT, TERM, KILL, SEGV.
error A message from the client indicating that the command was terminated unexpectedly due to an
error.
When performing I/O logging, the client should wait for a commit_point corresponding to the final
IoBuffer before closing the connection unless the final commit_point has already been received.
RestartMessage restart_msg
message RestartMessage {
string log_id = 1;
TimeSpec resume_point = 2;
}
A RestartMessage is sent by the client to resume sending an existing I/O log that was previously
interrupted. It contains the following members:
log_id The the server-side name for an I/O log that was previously sent to the client by the server.
This may be a path name on the server or some other kind of server-side identifier.
resume_point
The point in time after which to resume the I/O log. This is in the form of a TimeSpec
representing the amount of time since the command started, not the wall clock time. The
resume_point should correspond to a commit_point previously sent to the client by the server. If
the server receives a RestartMessage containing a resume_point it has not previously seen, an
error will be returned to the client and the connection will be dropped.
If a RestartMessage is sent, the client must not send an AcceptMessage or RejectMessage.
AlertMessage alert_msg
message AlertMessage {
TimeSpec alert_time = 1;
string reason = 2;
repeated InfoMessage info_msgs = 3;
}
An AlertMessage is sent by the client to indicate a problem detected by the security policy while the
command is running that should be stored in the event log. It contains the following members:
alert_time
The wall clock time when the alert occurred.
reason The reason for the alert.
info_msgs
An optional array of InfoMessage describing the user who submitted the command as well as the
execution environment of the command. This information is used to generate an event log entry.
IoBuffer ttyin_buf | ttyout_buf | stdin_buf | stdout_buf | stderr_buf
message IoBuffer {
TimeSpec delay = 1;
bytes data = 2;
}
An IoBuffer is used to represent data from terminal input, terminal output, standard input, standard
output, or standard error. It contains the following members:
delay The elapsed time since the last record in the form of a TimeSpec. The delay should be calculated
using a monotonic clock where possible.
data The binary I/O log data from terminal input, terminal output, standard input, standard output, or
standard error.
ChangeWindowSize winsize_event
message ChangeWindowSize {
TimeSpec delay = 1;
int32 rows = 2;
int32 cols = 3;
}
A ChangeWindowSize message is sent by the client when the terminal running the command changes size. It
contains the following members:
delay The elapsed time since the last record in the form of a TimeSpec. The delay should be calculated
using a monotonic clock where possible.
rows The new number of terminal rows.
cols The new number of terminal columns.
CommandSuspend suspend_event
message CommandSuspend {
TimeSpec delay = 1;
string signal = 2;
}
A CommandSuspend message is sent by the client when the command is either suspended or resumed. It
contains the following members:
delay The elapsed time since the last record in the form of a TimeSpec. The delay should be calculated
using a monotonic clock where possible.
signal The signal name without the leading “SIG”. For example, STOP, TSTP, CONT.
Server Messages
A ServerMessage is a container used to encapsulate all the possible message types the server may send to
a client.
message ServerMessage {
oneof type {
ServerHello hello = 1;
TimeSpec commit_point = 2;
string log_id = 3;
string error = 4;
string abort = 5;
}
}
The different ServerMessage sub-messages the server may sent to the client are described below.
ServerHello hello
message ServerHello {
string server_id = 1;
string redirect = 2;
repeated string servers = 3;
bool subcommands = 4;
}
The ServerHello message consists of server information sent when the client first connects. It contains
the following members:
server_id
A free-form server description. Usually this includes the name and version of the implementation
running on the log server. This member is always present.
redirect
A host and port separated by a colon (‘’): that the client should connect to instead. The host
may be a host name, an IPv4 address, or an IPv6 address in square brackets. This may be used for
server load balancing. The server will disconnect after sending the ServerHello when it includes
a redirect.
servers
A list of other known log servers. This can be used to implement log server redundancy and
allows the client to discover all other log servers simply by connecting to one known server.
This member may be omitted when there is only a single log server.
subcommands
If set, the server supports logging additional commands during a session. The client may send an
AcceptMessage or RejectMessage when sudo is running in intercept mode. In this mode, commands
spawned from the initial command authorized by sudo are subject to policy restrictions and/or are
logged. If subcommands is false, the client must not attempt to log additional commands.
TimeSpec commit_point
A periodic time stamp sent by the server to indicate when I/O log buffers have been committed to storage.
This message is not sent after every IoBuffer but rather at a server-configurable interval. When the
server receives an ExitMessage, it will respond with a commit_point corresponding to the last received
IoBuffer before closing the connection.
string log_id
The server-side ID of the I/O log being stored, sent in response to an AcceptMessage where expect_iobufs
is true.
string error
A fatal server-side error. The server will close the connection after sending the error message.
string abort
An abort message from the server indicates that the client should kill the command and terminate the
session. It may be used to implement simple server-side policy. The server will close the connection
after sending the abort message.
Protocol flow of control
The expected protocol flow is as follows:
1. Client connects to the first available server. If the client is configured to use TLS, a TLS
handshake will be attempted.
2. Client sends ClientHello. This is currently optional but allows the server to detect a non-TLS
connection on the TLS port.
3. Server sends ServerHello.
4. Client responds with either AcceptMessage, RejectMessage, or RestartMessage.
5. If client sent a AcceptMessage with expect_iobufs set, server creates a new I/O log and responds
with a log_id.
6. Client sends zero or more IoBuffer messages.
7. Server periodically responds to IoBuffer messages with a commit_point.
8. Client sends an ExitMessage when the command exits or is killed.
9. Server sends the final commit_point if one is pending.
10. Server closes the connection. After receiving the final commit_point, the client shuts down its
side of the TLS connection if TLS is in use, and closes the connection.
11. Server shuts down its side of the TLS connection if TLS is in use, and closes the connection.
At any point, the server may send an error or abort message to the client at which point the server will
close the connection. If an abort message is received, the client should terminate the running command.
EVENT LOG VARIABLES
AcceptMessage, AlertMessage and RejectMessage classes contain an array of InfoMessage that should contain
information about the user who submitted the command as well as information about the execution
environment of the command if it was accepted.
Some variables have a client, run, or submit prefix. These prefixes are used to eliminate ambiguity for
variables that could apply to the client program, the user submitting the command, or the command being
run. Variables with a client prefix pertain to the program performing the connection to the log server,
for example sudo. Variables with a run prefix pertain to the command that the user requested be run.
Variables with a submit prefix pertain to the user submitting the request (the user running sudo).
The following InfoMessage entries are required:
Key Type Description
command string command that was submitted
runuser string name of user the command was run as
submithost string name of host the command was submitted on
submituser string name of user submitting the command
The following InfoMessage entries are recognized, but not required:
Key Type Description
clientargv StringList client's original argument vector
clientpid int64 client's process ID
clientppid int64 client's parent process ID
clientsid int64 client's terminal session ID
columns int64 number of columns in the terminal
lines int64 number of lines in the terminal
runargv StringList argument vector of command to run
runchroot string root directory of command to run
runcwd string running command's working directory
runenv StringList the running command's environment
rungid int64 primary group-ID of the command
rungids NumberList supplementary group-IDs for the command
rungroup string primary group name of the command
rungroups StringList supplementary group names for the command
runuid int64 run user's user-ID
submitcwd string submit user's current working directory
submitenv StringList the submit user's environment
submitgid int64 submit user's primary group-ID
submitgids NumberList submit user's supplementary group-IDs
submitgroup string submitting user's primary group name
submitgroups StringList submit user's supplementary group names
submituid int64 submit user's user-ID
ttyname string the terminal the command was submitted from
The server must accept other variables not listed above but may ignore them.
EXAMPLES
The Protocol Buffers description of the log server protocol, using “proto3” syntax, is included in full
below.
syntax = "proto3";
/*
* Client message to the server. Messages on the wire are
* prefixed with a 32-bit size in network byte order.
*/
message ClientMessage {
oneof type {
AcceptMessage accept_msg = 1;
RejectMessage reject_msg = 2;
ExitMessage exit_msg = 3;
RestartMessage restart_msg = 4;
AlertMessage alert_msg = 5;
IoBuffer ttyin_buf = 6;
IoBuffer ttyout_buf = 7;
IoBuffer stdin_buf = 8;
IoBuffer stdout_buf = 9;
IoBuffer stderr_buf = 10;
ChangeWindowSize winsize_event = 11;
CommandSuspend suspend_event = 12;
}
}
/* Equivalent of POSIX struct timespec */
message TimeSpec {
int64 tv_sec = 1; /* seconds */
int32 tv_nsec = 2; /* nanoseconds */
}
/* I/O buffer with keystroke data */
message IoBuffer {
TimeSpec delay = 1; /* elapsed time since last record */
bytes data = 2; /* keystroke data */
}
/*
* Key/value pairs, like Privilege Manager struct info.
* The value may be a number, a string, or a list of strings.
*/
message InfoMessage {
message StringList {
repeated string strings = 1;
}
message NumberList {
repeated int64 numbers = 1;
}
string key = 1;
oneof value {
int64 numval = 2;
string strval = 3;
StringList strlistval = 4;
NumberList numlistval = 5;
}
}
/*
* Event log data for command accepted by the policy.
*/
message AcceptMessage {
TimeSpec submit_time = 1; /* when command was submitted */
repeated InfoMessage info_msgs = 2; /* key,value event log data */
bool expect_iobufs = 3; /* true if I/O logging enabled */
}
/*
* Event log data for command rejected by the policy.
*/
message RejectMessage {
TimeSpec submit_time = 1; /* when command was submitted */
string reason = 2; /* reason command was rejected */
repeated InfoMessage info_msgs = 3; /* key,value event log data */
}
/* Message sent by client when command exits. */
/* Might revisit runtime and use end_time instead */
message ExitMessage {
TimeSpec run_time = 1; /* total elapsed run time */
int32 exit_value = 2; /* 0-255 */
bool dumped_core = 3; /* true if command dumped core */
string signal = 4; /* signal name if killed by signal */
string error = 5; /* if killed due to other error */
}
/* Alert message, policy module-specific. */
message AlertMessage {
TimeSpec alert_time = 1; /* time alert message occurred */
string reason = 2; /* policy alert error string */
repeated InfoMessage info_msgs = 3; /* key,value event log data */
}
/* Used to restart an existing I/O log on the server. */
message RestartMessage {
string log_id = 1; /* ID of log being restarted */
TimeSpec resume_point = 2; /* resume point (elapsed time) */
}
/* Window size change event. */
message ChangeWindowSize {
TimeSpec delay = 1; /* elapsed time since last record */
int32 rows = 2; /* new number of rows */
int32 cols = 3; /* new number of columns */
}
/* Command suspend/resume event. */
message CommandSuspend {
TimeSpec delay = 1; /* elapsed time since last record */
string signal = 2; /* signal that caused suspend/resume */
}
/*
* Server messages to the client. Messages on the wire are
* prefixed with a 32-bit size in network byte order.
*/
message ServerMessage {
oneof type {
ServerHello hello = 1; /* server hello message */
TimeSpec commit_point = 2; /* cumulative time of records stored */
string log_id = 3; /* ID of server-side I/O log */
string error = 4; /* error message from server */
string abort = 5; /* abort message, kill command */
}
}
/* Hello message from server when client connects. */
message ServerHello {
string server_id = 1; /* free-form server description */
string redirect = 2; /* optional redirect if busy */
repeated string servers = 3; /* optional list of known servers */
}
SEE ALSO
sudo_logsrvd.conf(5), sudoers(5), sudo(8), sudo_logsrvd(8)
Protocol Buffers, https://developers.google.com/protocol-buffers/.
AUTHORS
Many people have worked on sudo over the years; this version consists of code written primarily by:
Todd C. Miller
See the CONTRIBUTORS.md file in the sudo distribution (https://www.sudo.ws/about/contributors/) for an
exhaustive list of people who have contributed to sudo.
BUGS
If you believe you have found a bug in sudo, you can submit a bug report at https://bugzilla.sudo.ws/
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.
DISCLAIMER
sudo is provided “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.md file distributed with sudo or https://www.sudo.ws/about/license/ for complete details.
Sudo 1.9.15p5 September 13, 2022 SUDO_LOGSRV.PROTO(5)