Ubuntu Manpage: sudoers_timestamp — Sudoers Time Stamp Format

Provided by: sudo_1.9.9-1ubuntu2.4_amd64

NAME

     sudoers_timestamp — Sudoers Time Stamp Format

DESCRIPTION

The sudoers plugin uses per-user time stamp files for credential caching. Once a user has
been authenticated, they may use sudo without a password for a short period of time (15
minutes unless overridden by the timestamp_timeout option). By default, sudoers uses a
separate record for each terminal, which means that a user's login sessions are
authenticated separately. The timestamp_type option can be used to select the type of time
stamp record sudoers will use.

A multi-record time stamp file format was introduced in sudo 1.8.10 that uses a single file
per user. Previously, a separate file was used for each user and terminal combination
unless tty-based time stamps were disabled. The new format is extensible and records of
multiple types and versions may coexist within the same file.

All records, regardless of type or version, begin with a 16-bit version number and a 16-bit
record size.

Time stamp records have the following structure:

/* Time stamp entry types */
#define TS_GLOBAL 0x01 /* not restricted by tty or ppid */
#define TS_TTY 0x02 /* restricted by tty */
#define TS_PPID 0x03 /* restricted by ppid */
#define TS_LOCKEXCL 0x04 /* special lock record */

/* Time stamp flags */
#define TS_DISABLED 0x01 /* entry disabled */
#define TS_ANYUID 0x02 /* ignore uid, only valid in key */

struct timestamp_entry {
unsigned short version; /* version number */
unsigned short size; /* entry size */
unsigned short type; /* TS_GLOBAL, TS_TTY, TS_PPID */
unsigned short flags; /* TS_DISABLED, TS_ANYUID */
uid_t auth_uid; /* uid to authenticate as */
pid_t sid; /* session ID associated with tty/ppid */
struct timespec start_time; /* session/ppid start time */
struct timespec ts; /* time stamp (CLOCK_MONOTONIC) */
union {
dev_t ttydev; /* tty device number */
pid_t ppid; /* parent pid */
} u;
};

The timestamp_entry struct fields are as follows:

version
The version number of the timestamp_entry struct. New entries are created with a
version number of 2. Records with different version numbers may coexist in the same
file but are not inter-operable.

size The size of the record in bytes.

type The record type, currently TS_GLOBAL, TS_TTY, or TS_PPID.

flags
Zero or more record flags which can be bit-wise ORed together. Supported flags are
TS_DISABLED, for records disabled via sudo -k and TS_ANYUID, which is used only when
matching records.

auth_uid
The user-ID that was used for authentication. Depending on the value of the rootpw,
runaspw and targetpw options, the user-ID may be that of the invoking user, the root
user, the default runas user or the target user.

sid The ID of the user's terminal session, if present. The session ID is only used when
matching records of type TS_TTY.

start_time
The start time of the session leader for records of type TS_TTY or of the parent
process for records of type TS_PPID. The start_time is used to help prevent re-use of
a time stamp record after a user has logged out. Not all systems support a method to
easily retrieve a process's start time. The start_time field was added in sudoers
version 1.8.22 for the second revision of the timestamp_entry struct.

ts The actual time stamp. A monotonic time source (which does not move backward) is used
if the system supports it. Where possible, sudoers uses a monotonic timer that
increments even while the system is suspended. The value of ts is updated each time a
command is run via sudo. If the difference between ts and the current time is less
than the value of the timestamp_timeout option, no password is required.

u.ttydev
The device number of the terminal associated with the session for records of type
TS_TTY.

u.ppid
The ID of the parent process for records of type TS_PPID.

LOCKING

     In sudoers versions 1.8.10 through 1.8.14, the entire time stamp file was locked for
     exclusive access when reading or writing to the file.  Starting in sudoers 1.8.15,
     individual records are locked in the time stamp file instead of the entire file and the lock
     is held for a longer period of time.  This scheme is described below.

     The first record in the time stamp file is of type TS_LOCKEXCL and is used as a lock record
     to prevent more than one sudo process from adding a new record at the same time.  Once the
     desired time stamp record has been located or created (and locked), the TS_LOCKEXCL record
     is unlocked.  The lock on the individual time stamp record, however, is held until
     authentication is complete.  This allows sudoers to avoid prompting for a password multiple
     times when it is used more than once in a pipeline.

     Records of type TS_GLOBAL cannot be locked for a long period of time since doing so would
     interfere with other sudo processes.  Instead, a separate lock record is used to prevent
     multiple sudo processes using the same terminal (or parent process ID) from prompting for a
     password as the same time.

HISTORY

Originally, sudo used a single zero-length file per user and the file's modification time
was used as the time stamp. Later versions of sudo added restrictions on the ownership of
the time stamp files and directory as well as checks on the validity of the time stamp
itself. Notable changes were introduced in the following sudo versions:

1.4.0
Support for tty-based time stamp file was added by appending the terminal name to the
time stamp file name.

1.6.2
The time stamp file was replaced by a per-user directory which contained any tty-based
time stamp files.

1.6.3p2
The target user name was added to the time stamp file name when the targetpw option
was set.

1.7.3
Information about the terminal device was stored in tty-based time stamp files for
validity checks. This included the terminal device numbers, inode number and, on
systems where it was not updated when the device was written to, the inode change
time. This helped prevent re-use of the time stamp file after logout.

1.8.6p7
The terminal session ID was added to tty-based time stamp files to prevent re-use of
the time stamp by the same user in a different terminal session. It also helped
prevent re-use of the time stamp file on systems where the terminal device's inode
change time was updated by writing.

1.8.10
A new, multi-record time stamp file format was introduced that uses a single file per
user. The terminal device's change time was not included since most systems now
update the change time after a write is performed as required by POSIX.

1.8.15
Individual records are locked in the time stamp file instead of the entire file and
the lock is held until authentication is complete.

1.8.22
The start time of the terminal session leader or parent process is now stored in non-
global time stamp records. This prevents re-use of the time stamp file after logout
in most cases.

Support was added for the kernel-based tty time stamps available in OpenBSD which do
not use an on-disk time stamp file.

AUTHORS

     Many people have worked on sudo over the years; this version consists of code written
     primarily by:

           Todd C. Miller

     See the CONTRIBUTORS file in the sudo distribution (https://www.sudo.ws/contributors.html)
     for an exhaustive list of people who have contributed to sudo.

BUGS

     If you feel you have found a bug in sudo, please 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 file distributed with sudo or https://www.sudo.ws/license.html
     for complete details.