table of contents
SUDO_PLUGIN(5) | File Formats Manual | SUDO_PLUGIN(5) |
NAME¶
sudo_plugin
— Sudo
Plugin API
DESCRIPTION¶
Starting with version 1.8, sudo
supports a
plugin API for policy and session logging. Plugins may be compiled as
dynamic shared objects (the default on systems that support them) or
compiled statically into the sudo
binary itself. By
default, the sudoers
policy plugin and an associated
I/O logging plugin are used. Via the plugin API,
sudo
can be configured to use alternate policy
and/or I/O logging plugins provided by third parties. The plugins to be used
are specified in the sudo.conf(5) file.
The API is versioned with a major and minor number. The minor version number is incremented when additions are made. The major number is incremented when incompatible changes are made. A plugin should be check the version passed to it and make sure that the major version matches.
The plugin API is defined by the
sudo_plugin.h
header file.
Policy plugin API¶
A policy plugin must declare and populate a
policy_plugin
struct in the global scope. This
structure contains pointers to the functions that implement the
sudo
policy checks. The name of the symbol should be
specified in sudo.conf(5) along with a path to the plugin
so that sudo
can load it.
struct policy_plugin { #define SUDO_POLICY_PLUGIN 1 unsigned int type; /* always SUDO_POLICY_PLUGIN */ unsigned int version; /* always SUDO_API_VERSION */ int (*open)(unsigned int version, sudo_conv_t conversation, sudo_printf_t plugin_printf, char * const settings[], char * const user_info[], char * const user_env[], char * const plugin_options[]); void (*close)(int exit_status, int error); int (*show_version)(int verbose); int (*check_policy)(int argc, char * const argv[], char *env_add[], char **command_info[], char **argv_out[], char **user_env_out[]); int (*list)(int argc, char * const argv[], int verbose, const char *list_user); int (*validate)(void); void (*invalidate)(int remove); int (*init_session)(struct passwd *pwd, char **user_env[]); void (*register_hooks)(int version, int (*register_hook)(struct sudo_hook *hook)); void (*deregister_hooks)(int version, int (*deregister_hook)(struct sudo_hook *hook)); };
The policy_plugin struct has the following fields:
- type
- The
type
field should always be set to SUDO_POLICY_PLUGIN. - version
- The
version
field should be set toSUDO_API_VERSION
.This allows
sudo
to determine the API version the plugin was built against. - open
-
int (*open)(unsigned int version, sudo_conv_t conversation, sudo_printf_t plugin_printf, char * const settings[], char * const user_info[], char * const user_env[], char * const plugin_options[]);
Returns 1 on success, 0 on failure, -1 if a general error occurred, or -2 if there was a usage error. In the latter case,
sudo
will print a usage message before it exits. If an error occurs, the plugin may optionally call theconversation
() orplugin_printf
() function withSUDO_CONF_ERROR_MSG
to present additional error information to the user.The function arguments are as follows:
- version
- The version passed in by
sudo
allows the plugin to determine the major and minor version number of the plugin API supported bysudo
. - conversation
- A pointer to the
conversation
() function that can be used by the plugin to interact with the user (see below). Returns 0 on success and -1 on failure. - plugin_printf
- A pointer to a
printf
()-style function that may be used to display informational or error messages (see below). Returns the number of characters printed on success and -1 on failure. - settings
- A vector of user-supplied
sudo
settings in the form of “name=value” strings. The vector is terminated by aNULL
pointer. These settings correspond to flags the user specified when runningsudo
. As such, they will only be present when the corresponding flag has been specified on the command line.When parsing settings, the plugin should split on the first equal sign (‘
=
’) since the name field will never include one itself but the value might.- bsdauth_type=string
- Authentication type, if specified by the
-a
flag, to use on systems where BSD authentication is supported. - closefrom=number
- If specified, the user has requested via the
-C
flag thatsudo
close all files descriptors with a value of number or higher. The plugin may optionally pass this, or another value, back in the command_info list. - debug_flags=string
- A debug file path name followed by a space and a comma-separated
list of debug flags that correspond to the plugin's
Debug
entry in sudo.conf(5), if there is one. The flags are passed to the plugin exactly as they appear in sudo.conf(5). The syntax used bysudo
and thesudoers
plugin is subsystem@priority but a plugin is free to use a different format so long as it does not include a comma (‘,
’). Prior tosudo
1.8.12, there was no way to specify plugin-specific debug_flags so the value was always the same as that used by thesudo
front end and did not include a path name, only the flags themselves. As of version 1.7 of the plugin interface,sudo
will only pass debug_flags if sudo.conf(5) contains a plugin-specificDebug
entry. - debug_level=number
- This setting has been deprecated in favor of debug_flags.
- ignore_ticket=bool
- Set to true if the user specified the
-k
flag along with a command, indicating that the user wishes to ignore any cached authentication credentials. implied_shell to true. This allowssudo
with no arguments to be used similarly to su(1). If the plugin does not to support this usage, it may return a value of -2 from thecheck_policy
() function, which will causesudo
to print a usage message and exit. - implied_shell=bool
- If the user does not specify a program on the command line,
sudo
will pass the plugin the path to the user's shell and set - login_class=string
- BSD login class to use when setting resource limits and nice
value, if specified by the
-c
flag. - login_shell=bool
- Set to true if the user specified the
-i
flag, indicating that the user wishes to run a login shell. - max_groups=int
- The maximum number of groups a user may belong to. This will only be present if there is a corresponding setting in sudo.conf(5).
- network_addrs=list
- A space-separated list of IP network addresses and netmasks in the
form “addr/netmask”, e.g.
“192.168.1.2/255.255.255.0”. The address and netmask
pairs may be either IPv4 or IPv6, depending on what the operating
system supports. If the address contains a colon
(‘
:
’), it is an IPv6 address, else it is IPv4. - noninteractive=bool
- Set to true if the user specified the
-n
flag, indicating thatsudo
should operate in non-interactive mode. The plugin may reject a command run in non-interactive mode if user interaction is required. - plugin_dir=string
- The default plugin directory used by the
sudo
front end. This is the default directory set at compile time and may not correspond to the directory the running plugin was loaded from. It may be used by a plugin to locate support files. - plugin_path=string
- The path name of plugin loaded by the
sudo
front end. The path name will be a fully-qualified unless the plugin was statically compiled intosudo
. - preserve_environment=bool
- Set to true if the user specified the
-E
flag, indicating that the user wishes to preserve the environment. - preserve_groups=bool
- Set to true if the user specified the
-P
flag, indicating that the user wishes to preserve the group vector instead of setting it based on the runas user. - progname=string
- The command name that sudo was run as, typically “sudo” or “sudoedit”.
- prompt=string
- The prompt to use when requesting a password, if specified via the
-p
flag. - remote_host=string
- The name of the remote host to run the command on, if specified
via the
-h
option. Support for running the command on a remote host is meant to be implemented via a helper program that is executed in place of the user-specified command. Thesudo
front end is only capable of executing commands on the local host. Only available starting with API version 1.4. - run_shell=bool
- Set to true if the user specified the
-s
flag, indicating that the user wishes to run a shell. - runas_group=string
- The group name or gid to run the command as, if specified via the
-g
flag. - runas_user=string
- The user name or uid to run the command as, if specified via the
-u
flag. - selinux_role=string
- SELinux role to use when executing the command, if specified by
the
-r
flag. - selinux_type=string
- SELinux type to use when executing the command, if specified by
the
-t
flag. - set_home=bool
- Set to true if the user specified the
-H
flag. If true, set theHOME
environment variable to the target user's home directory. - sudoedit=bool
- Set to true when the
-e
flag is is specified or if invoked assudoedit
. The plugin shall substitute an editor into argv in thecheck_policy
() function or return -2 with a usage error if the plugin does not support sudoedit. For more information, see the check_policy section. - timeout=string
- User-specified command timeout. Not all plugins support command timeouts and the ability for the user to set a timeout may be restricted by policy. The format of the timeout string is plugin-specific.
Additional settings may be added in the future so the plugin should silently ignore settings that it does not recognize.
- user_info
- A vector of information about the user running the command in the form
of “name=value” strings. The vector is terminated by a
NULL
pointer.When parsing user_info, the plugin should split on the first equal sign (‘
=
’) since the name field will never include one itself but the value might.- cols=int
- The number of columns the user's terminal supports. If there is no terminal device available, a default value of 80 is used.
- cwd=string
- The user's current working directory.
- egid=gid_t
- The effective group ID of the user invoking
sudo
. - euid=uid_t
- The effective user ID of the user invoking
sudo
. - gid=gid_t
- The real group ID of the user invoking
sudo
. - groups=list
- The user's supplementary group list formatted as a string of comma-separated group IDs.
- host=string
- The local machine's hostname as returned by the gethostname(2) system call.
- lines=int
- The number of lines the user's terminal supports. If there is no terminal device available, a default value of 24 is used.
- pgid=int
- The ID of the process group that the running
sudo
process is a member of. Only available starting with API version 1.2. - pid=int
- The process ID of the running
sudo
process. Only available starting with API version 1.2. - plugin_options
- Any (non-comment) strings immediately after the plugin path are
passed as arguments to the plugin. These arguments are split on a
white space boundary and are passed to the plugin in the form of a
NULL
-terminated array of strings. If no arguments were specified, plugin_options will be theNULL
pointer.NOTE: the plugin_options parameter is only available starting with API version 1.2. A plugin must check the API version specified by the
sudo
front end before using plugin_options. Failure to do so may result in a crash. - ppid=int
- The parent process ID of the running
sudo
process. Only available starting with API version 1.2. - sid=int
- The session ID of the running
sudo
process or 0 ifsudo
is not part of a POSIX job control session. Only available starting with API version 1.2. - tcpgid=int
- The ID of the foreground process group associated with the
terminal device associated with the
sudo
process or -1 if there is no terminal present. Only available starting with API version 1.2. - tty=string
- The path to the user's terminal device. If the user has no
terminal device associated with the session, the value will be
empty, as in “
tty=
”. - uid=uid_t
- The real user ID of the user invoking
sudo
. - umask=octal
- The invoking user's file creation mask. Only available starting with API version 1.10.
- user=string
- The name of the user invoking
sudo
.
- user_env
- The user's environment in the form of a
NULL
-terminated vector of “name=value” strings.When parsing user_env, the plugin should split on the first equal sign (‘
=
’) since the name field will never include one itself but the value might.
- close
-
void (*close)(int exit_status, int error);
The
close
() function is called when the command being run bysudo
finishes.The function arguments are as follows:
- exit_status
- The command's exit status, as returned by the
wait(2) system call. The value of
exit_status
is undefined iferror
is non-zero. - error
- If the command could not be executed, this is set to the value of
errno
set by the execve(2) system call. The plugin is responsible for displaying error information via theconversation
() orplugin_printf
() function. If the command was successfully executed, the value oferror
is 0.
If no
close
() function is defined, no I/O logging plugins are loaded, and neither the timeout not use_pty options are set in thecommand_info
list, thesudo
front end may execute the command directly instead of running it as a child process. - show_version
-
int (*show_version)(int verbose);
The
show_version
() function is called bysudo
when the user specifies the-V
option. The plugin may display its version information to the user via theconversation
() orplugin_printf
() function usingSUDO_CONV_INFO_MSG
. If the user requests detailed version information, the verbose flag will be set. - check_policy
-
int (*check_policy)(int argc, char * const argv[] char *env_add[], char **command_info[], char **argv_out[], char **user_env_out[]);
The
check_policy
() function is called bysudo
to determine whether the user is allowed to run the specified commands.If the sudoedit option was enabled in the settings array passed to the
open
() function, the user has requested sudoedit mode. sudoedit is a mechanism for editing one or more files where an editor is run with the user's credentials instead of with elevated privileges.sudo
achieves this by creating user-writable temporary copies of the files to be edited and then overwriting the originals with the temporary copies after editing is complete. If the plugin supports sudoedit, it should choose the editor to be used, potentially from a variable in the user's environment, such asEDITOR
, and include it in argv_out (note that environment variables may include command line flags). The files to be edited should be copied from argv into argv_out, separated from the editor and its arguments by a “--
” element. The “--
” will be removed bysudo
before the editor is executed. The plugin should also set sudoedit=true in the command_info list.The
check_policy
() function returns 1 if the command is allowed, 0 if not allowed, -1 for a general error, or -2 for a usage error or if sudoedit was specified but is unsupported by the plugin. In the latter case,sudo
will print a usage message before it exits. If an error occurs, the plugin may optionally call theconversation
() orplugin_printf
() function withSUDO_CONF_ERROR_MSG
to present additional error information to the user.The function arguments are as follows:
- argc
- The number of elements in argv, not counting the
final
NULL
pointer. - argv
- The argument vector describing the command the user wishes to run, in
the same form as what would be passed to the
execve(2) system call. The vector is terminated by a
NULL
pointer. - env_add
- Additional environment variables specified by the user on the command
line in the form of a
NULL
-terminated vector of “name=value” strings. The plugin may reject the command if one or more variables are not allowed to be set, or it may silently ignore such variables.When parsing env_add, the plugin should split on the first equal sign (‘
=
’) since the name field will never include one itself but the value might. - command_info
- Information about the command being run in the form of
“name=value” strings. These values are used by
sudo
to set the execution environment when running a command. The plugin is responsible for creating and populating the vector, which must be terminated with aNULL
pointer. The following values are recognized bysudo
:- chroot=string
- The root directory to use when running the command.
- closefrom=number
- If specified,
sudo
will close all files descriptors with a value of number or higher. - command=string
- Fully qualified path to the command to be executed.
- cwd=string
- The current working directory to change to when executing the command.
- exec_background=bool
- By default,
sudo
runs a command as the foreground process as long assudo
itself is running in the foreground. When exec_background is enabled and the command is being run in a pty (due to I/O logging or the use_pty setting), the command will be run as a background process. Attempts to read from the controlling terminal (or to change terminal settings) will result in the command being suspended with theSIGTTIN
signal (orSIGTTOU
in the case of terminal settings). If this happens whensudo
is a foreground process, the command will be granted the controlling terminal and resumed in the foreground with no user intervention required. The advantage of initially running the command in the background is thatsudo
need not read from the terminal unless the command explicitly requests it. Otherwise, any terminal input must be passed to the command, whether it has required it or not (the kernel buffers terminals so it is not possible to tell whether the command really wants the input). This is different from historic sudo behavior or when the command is not being run in a pty.For this to work seamlessly, the operating system must support the automatic restarting of system calls. Unfortunately, not all operating systems do this by default, and even those that do may have bugs. For example, macOS fails to restart the
tcgetattr
() andtcsetattr
() system calls (this is a bug in macOS). Furthermore, because this behavior depends on the command stopping with theSIGTTIN
orSIGTTOU
signals, programs that catch these signals and suspend themselves with a different signal (usuallySIGTOP
) will not be automatically foregrounded. Some versions of the linux su(1) command behave this way. Because of this, a plugin should not set exec_background unless it is explicitly enabled by the administrator and there should be a way to enabled or disable it on a per-command basis.This setting has no effect unless I/O logging is enabled or use_pty is enabled.
- execfd=number
- If specified,
sudo
will use the fexecve(2) system call to execute the command instead of execve(2). The specified number must refer to an open file descriptor. - iolog_compress=bool
- Set to true if the I/O logging plugins, if any, should compress the log data. This is a hint to the I/O logging plugin which may choose to ignore it.
- iolog_group=string
- The group that will own newly created I/O log files and directories. This is a hint to the I/O logging plugin which may choose to ignore it.
- iolog_mode=octal
- The file permission mode to use when creating I/O log files and directories. This is a hint to the I/O logging plugin which may choose to ignore it.
- iolog_user=string
- The user that will own newly created I/O log files and directories. This is a hint to the I/O logging plugin which may choose to ignore it.
- iolog_path=string
- Fully qualified path to the file or directory in which I/O log is to be stored. This is a hint to the I/O logging plugin which may choose to ignore it. If no I/O logging plugin is loaded, this setting has no effect.
- iolog_stdin=bool
- Set to true if the I/O logging plugins, if any, should log the standard input if it is not connected to a terminal device. This is a hint to the I/O logging plugin which may choose to ignore it.
- iolog_stdout=bool
- Set to true if the I/O logging plugins, if any, should log the standard output if it is not connected to a terminal device. This is a hint to the I/O logging plugin which may choose to ignore it.
- iolog_stderr=bool
- Set to true if the I/O logging plugins, if any, should log the standard error if it is not connected to a terminal device. This is a hint to the I/O logging plugin which may choose to ignore it.
- iolog_ttyin=bool
- Set to true if the I/O logging plugins, if any, should log all terminal input. This only includes input typed by the user and not from a pipe or redirected from a file. This is a hint to the I/O logging plugin which may choose to ignore it.
- iolog_ttyout=bool
- Set to true if the I/O logging plugins, if any, should log all terminal output. This only includes output to the screen, not output to a pipe or file. This is a hint to the I/O logging plugin which may choose to ignore it.
- login_class=string
- BSD login class to use when setting resource limits and nice value (optional). This option is only set on systems that support login classes.
- nice=int
- Nice value (priority) to use when executing the command. The nice value, if specified, overrides the priority associated with the login_class on BSD systems.
- noexec=bool
- If set, prevent the command from executing other programs.
- preserve_fds=list
- A comma-separated list of file descriptors that should be preserved, regardless of the value of the closefrom setting. Only available starting with API version 1.5.
- preserve_groups=bool
- If set,
sudo
will preserve the user's group vector instead of initializing the group vector based onrunas_user
. - runas_egid=gid
- Effective group ID to run the command as. If not specified, the value of runas_gid is used.
- runas_euid=uid
- Effective user ID to run the command as. If not specified, the value of runas_uid is used.
- runas_gid=gid
- Group ID to run the command as.
- runas_groups=list
- The supplementary group vector to use for the command in the form of a comma-separated list of group IDs. If preserve_groups is set, this option is ignored.
- runas_uid=uid
- User ID to run the command as.
- selinux_role=string
- SELinux role to use when executing the command.
- selinux_type=string
- SELinux type to use when executing the command.
- set_utmp=bool
- Create a utmp (or utmpx) entry when a pseudo-tty is allocated. By default, the new entry will be a copy of the user's existing utmp entry (if any), with the tty, time, type and pid fields updated.
- sudoedit=bool
- Set to true when in sudoedit mode. The plugin
may enable sudoedit mode even if
sudo
was not invoked assudoedit
. This allows the plugin to perform command substitution and transparently enable sudoedit when the user attempts to run an editor. - sudoedit_checkdir=bool
- Set to false to disable directory writability checks in
sudoedit
. By default,sudoedit
1.8.16 and higher will check all directory components of the path to be edited for writability by the invoking user. Symbolic links will not be followed in writable directories andsudoedit
will refuse to edit a file located in a writable directory. These restrictions are not enforced whensudoedit
is run by root. The sudoedit_follow option can be set to false to disable this check. Only available starting with API version 1.8. - sudoedit_follow=bool
- Set to true to allow
sudoedit
to edit files that are symbolic links. By default,sudoedit
1.8.15 and higher will refuse to open a symbolic link. The sudoedit_follow option can be used to restore the older behavior and allowsudoedit
to open symbolic links. Only available starting with API version 1.8. - timeout=int
- Command timeout. If non-zero then when the timeout expires the command will be killed.
- umask=octal
- The file creation mask to use when executing the command.
- use_pty=bool
- Allocate a pseudo-tty to run the command in, regardless of whether
or not I/O logging is in use. By default,
sudo
will only run the command in a pty when an I/O log plugin is loaded. - utmp_user=string
- User name to use when constructing a new utmp (or utmpx) entry
when
set_utmp
is enabled. This option can be used to set the user field in the
utmp entry to the user the command runs as rather than the
invoking user. If not set,
sudo
will base the new entry on the invoking user's existing entry.
Unsupported values will be ignored.
- argv_out
- The
NULL
-terminated argument vector to pass to the execve(2) system call when executing the command. The plugin is responsible for allocating and populating the vector. - user_env_out
- The
NULL
-terminated environment vector to use when executing the command. The plugin is responsible for allocating and populating the vector.
- list
-
int (*list)(int verbose, const char *list_user, int argc, char * const argv[]);
List available privileges for the invoking user. Returns 1 on success, 0 on failure and -1 on error. On error, the plugin may optionally call the
conversation
() orplugin_printf
() function withSUDO_CONF_ERROR_MSG
to present additional error information to the user.Privileges should be output via the
conversation
() orplugin_printf
() function usingSUDO_CONV_INFO_MSG
,- verbose
- Flag indicating whether to list in verbose mode or not.
- list_user
- The name of a different user to list privileges for if the policy
allows it. If
NULL
, the plugin should list the privileges of the invoking user. - argc
- The number of elements in argv, not counting the
final
NULL
pointer. - argv
- If non-
NULL
, an argument vector describing a command the user wishes to check against the policy in the same form as what would be passed to the execve(2) system call. If the command is permitted by the policy, the fully-qualified path to the command should be displayed along with any command line arguments.
- validate
-
int (*validate)(void);
The
validate
() function is called whensudo
is run with the-v
flag. For policy plugins such assudoers
that cache authentication credentials, this function will validate and cache the credentials.The
validate
() function should beNULL
if the plugin does not support credential caching.Returns 1 on success, 0 on failure and -1 on error. On error, the plugin may optionally call the
conversation
() orplugin_printf
() function withSUDO_CONF_ERROR_MSG
to present additional error information to the user. - invalidate
-
void (*invalidate)(int remove);
The
invalidate
() function is called whensudo
is called with the-k
or-K
flag. For policy plugins such assudoers
that cache authentication credentials, this function will invalidate the credentials. If the remove flag is set, the plugin may remove the credentials instead of simply invalidating them.The
invalidate
() function should beNULL
if the plugin does not support credential caching. - init_session
-
int (*init_session)(struct passwd *pwd, char **user_envp[);
The
init_session
() function is called beforesudo
sets up the execution environment for the command. It is run in the parentsudo
process and before any uid or gid changes. This can be used to perform session setup that is not supported by command_info, such as opening the PAM session. Theclose
() function can be used to tear down the session that was opened byinit_session
.The pwd argument points to a passwd struct for the user the command will be run as if the uid the command will run as was found in the password database, otherwise it will be
NULL
.The user_env argument points to the environment the command will run in, in the form of a
NULL
-terminated vector of “name=value” strings. This is the same string passed back to the front end via the Policy Plugin's user_env_out parameter. If theinit_session
() function needs to modify the user environment, it should update the pointer stored in user_env. The expected use case is to merge the contents of the PAM environment (if any) with the contents of user_env. NOTE: the user_env parameter is only available starting with API version 1.2. A plugin must check the API version specified by thesudo
front end before using user_env. Failure to do so may result in a crash.Returns 1 on success, 0 on failure and -1 on error. On error, the plugin may optionally call the
conversation
() orplugin_printf
() function withSUDO_CONF_ERROR_MSG
to present additional error information to the user. - register_hooks
-
void (*register_hooks)(int version, int (*register_hook)(struct sudo_hook *hook));
The
register_hooks
() function is called by the sudo front end to register any hooks the plugin needs. If the plugin does not support hooks,register_hooks
should be set to theNULL
pointer.The version argument describes the version of the hooks API supported by the
sudo
front end.The
register_hook
() function should be used to register any supported hooks the plugin needs. It returns 0 on success, 1 if the hook type is not supported and -1 if the major version instruct hook
does not match the front end's major hook API version.See the Hook function API section below for more information about hooks.
NOTE: the
register_hooks
() function is only available starting with API version 1.2. If thesudo
front end doesn't support API version 1.2 or higher,register_hooks
will not be called. - deregister_hooks
-
void (*deregister_hooks)(int version, int (*deregister_hook)(struct sudo_hook *hook));
The
deregister_hooks
() function is called by the sudo front end to deregister any hooks the plugin has registered. If the plugin does not support hooks,deregister_hooks
should be set to theNULL
pointer.The version argument describes the version of the hooks API supported by the
sudo
front end.The
deregister_hook
() function should be used to deregister any hooks that were put in place by theregister_hook
() function. If the plugin tries to deregister a hook that the front end does not support,deregister_hook
will return an error.See the Hook function API section below for more information about hooks.
NOTE: the
deregister_hooks
() function is only available starting with API version 1.2. If thesudo
front end doesn't support API version 1.2 or higher,deregister_hooks
will not be called.
/* Plugin API version major/minor. */ #define SUDO_API_VERSION_MAJOR 1 #define SUDO_API_VERSION_MINOR 2 #define SUDO_API_MKVERSION(x, y) ((x << 16) | y) #define SUDO_API_VERSION SUDO_API_MKVERSION(SUDO_API_VERSION_MAJOR,\ SUDO_API_VERSION_MINOR) /* Getters and setters for API version */ #define SUDO_API_VERSION_GET_MAJOR(v) ((v) >> 16) #define SUDO_API_VERSION_GET_MINOR(v) ((v) & 0xffff) #define SUDO_API_VERSION_SET_MAJOR(vp, n) do { \ *(vp) = (*(vp) & 0x0000ffff) | ((n) << 16); \ } while(0) #define SUDO_API_VERSION_SET_MINOR(vp, n) do { \ *(vp) = (*(vp) & 0xffff0000) | (n); \ } while(0)
I/O plugin API¶
struct io_plugin { #define SUDO_IO_PLUGIN 2 unsigned int type; /* always SUDO_IO_PLUGIN */ unsigned int version; /* always SUDO_API_VERSION */ int (*open)(unsigned int version, sudo_conv_t conversation, sudo_printf_t plugin_printf, char * const settings[], char * const user_info[], char * const command_info[], int argc, char * const argv[], char * const user_env[], char * const plugin_options[]); void (*close)(int exit_status, int error); /* wait status or error */ int (*show_version)(int verbose); int (*log_ttyin)(const char *buf, unsigned int len); int (*log_ttyout)(const char *buf, unsigned int len); int (*log_stdin)(const char *buf, unsigned int len); int (*log_stdout)(const char *buf, unsigned int len); int (*log_stderr)(const char *buf, unsigned int len); void (*register_hooks)(int version, int (*register_hook)(struct sudo_hook *hook)); void (*deregister_hooks)(int version, int (*deregister_hook)(struct sudo_hook *hook)); int (*change_winsize)(unsigned int lines, unsigned int cols); };
When an I/O plugin is loaded, sudo
runs
the command in a pseudo-tty. This makes it possible to log the input and
output from the user's session. If any of the standard input, standard
output or standard error do not correspond to a tty,
sudo
will open a pipe to capture the I/O for logging
before passing it on.
The log_ttyin function receives the raw user input
from the terminal device (note that this will include input even when echo
is disabled, such as when a password is read). The log_ttyout function
receives output from the pseudo-tty that is suitable for replaying the
user's session at a later time. The
log_stdin
(),
log_stdout
() and
log_stderr
() functions are only called if the
standard input, standard output or standard error respectively correspond to
something other than a tty.
Any of the logging functions may be set to the
NULL
pointer if no logging is to be performed. If
the open function returns 0, no I/O will be sent to the plugin.
If a logging function returns an error (-1), the running command will be terminated and all of the plugin's logging functions will be disabled. Other I/O logging plugins will still receive any remaining input or output that has not yet been processed.
If an input logging function rejects the data by returning 0, the command will be terminated and the data will not be passed to the command, though it will still be sent to any other I/O logging plugins. If an output logging function rejects the data by returning 0, the command will be terminated and the data will not be written to the terminal, though it will still be sent to any other I/O logging plugins.
The io_plugin struct has the following fields:
- type
- The
type
field should always be set toSUDO_IO_PLUGIN
. - version
- The
version
field should be set toSUDO_API_VERSION
.This allows
sudo
to determine the API version the plugin was built against. - open
-
int (*open)(unsigned int version, sudo_conv_t conversation, sudo_printf_t plugin_printf, char * const settings[], char * const user_info[], int argc, char * const argv[], char * const user_env[], char * const plugin_options[]);
The
open
() function is run before thelog_ttyin
(),log_ttyout
(),log_stdin
(),log_stdout
(),log_stderr
(), orshow_version
() functions are called. It is only called if the version is being requested or if the policy plugin'scheck_policy
() function has returned successfully. It returns 1 on success, 0 on failure, -1 if a general error occurred, or -2 if there was a usage error. In the latter case,sudo
will print a usage message before it exits. If an error occurs, the plugin may optionally call theconversation
() orplugin_printf
() function withSUDO_CONF_ERROR_MSG
to present additional error information to the user.The function arguments are as follows:
- version
- The version passed in by
sudo
allows the plugin to determine the major and minor version number of the plugin API supported bysudo
. - conversation
- A pointer to the
conversation
() function that may be used by theshow_version
() function to display version information (seeshow_version
() below). Theconversation
() function may also be used to display additional error message to the user. Theconversation
() function returns 0 on success and -1 on failure. - plugin_printf
- A pointer to a
printf
()-style function that may be used by theshow_version
() function to display version information (see show_version below). Theplugin_printf
() function may also be used to display additional error message to the user. Theplugin_printf
() function returns number of characters printed on success and -1 on failure. - settings
- A vector of user-supplied
sudo
settings in the form of “name=value” strings. The vector is terminated by aNULL
pointer. These settings correspond to flags the user specified when runningsudo
. As such, they will only be present when the corresponding flag has been specified on the command line.When parsing settings, the plugin should split on the first equal sign (‘
=
’) since the name field will never include one itself but the value might.See the Policy plugin API section for a list of all possible settings.
- user_info
- A vector of information about the user running the command in the form
of “name=value” strings. The vector is terminated by a
NULL
pointer.When parsing user_info, the plugin should split on the first equal sign (‘
=
’) since the name field will never include one itself but the value might.See the Policy plugin API section for a list of all possible strings.
- argc
- The number of elements in argv, not counting the
final
NULL
pointer. - argv
- If non-
NULL
, an argument vector describing a command the user wishes to run in the same form as what would be passed to the execve(2) system call. - user_env
- The user's environment in the form of a
NULL
-terminated vector of “name=value” strings.When parsing user_env, the plugin should split on the first equal sign (‘
=
’) since the name field will never include one itself but the value might. - plugin_options
- Any (non-comment) strings immediately after the plugin path are
treated as arguments to the plugin. These arguments are split on a
white space boundary and are passed to the plugin in the form of a
NULL
-terminated array of strings. If no arguments were specified, plugin_options will be theNULL
pointer.NOTE: the plugin_options parameter is only available starting with API version 1.2. A plugin must check the API version specified by the
sudo
front end before using plugin_options. Failure to do so may result in a crash.
- close
-
void (*close)(int exit_status, int error);
The
close
() function is called when the command being run bysudo
finishes.The function arguments are as follows:
- exit_status
- The command's exit status, as returned by the
wait(2) system call. The value of
exit_status
is undefined iferror
is non-zero. - error
- If the command could not be executed, this is set to the value of
errno
set by the execve(2) system call. If the command was successfully executed, the value oferror
is 0.
- show_version
-
int (*show_version)(int verbose);
The
show_version
() function is called bysudo
when the user specifies the-V
option. The plugin may display its version information to the user via theconversation
() orplugin_printf
() function usingSUDO_CONV_INFO_MSG
. If the user requests detailed version information, the verbose flag will be set. - log_ttyin
-
int (*log_ttyin)(const char *buf, unsigned int len);
The
log_ttyin
() function is called whenever data can be read from the user but before it is passed to the running command. This allows the plugin to reject data if it chooses to (for instance if the input contains banned content). Returns 1 if the data should be passed to the command, 0 if the data is rejected (which will terminate the running command) or -1 if an error occurred.The function arguments are as follows:
- buf
- The buffer containing user input.
- len
- The length of buf in bytes.
- log_ttyout
-
int (*log_ttyout)(const char *buf, unsigned int len);
The
log_ttyout
() function is called whenever data can be read from the command but before it is written to the user's terminal. This allows the plugin to reject data if it chooses to (for instance if the output contains banned content). Returns 1 if the data should be passed to the user, 0 if the data is rejected (which will terminate the running command) or -1 if an error occurred.The function arguments are as follows:
- buf
- The buffer containing command output.
- len
- The length of buf in bytes.
- log_stdin
-
int (*log_stdin)(const char *buf, unsigned int len);
The
log_stdin
() function is only used if the standard input does not correspond to a tty device. It is called whenever data can be read from the standard input but before it is passed to the running command. This allows the plugin to reject data if it chooses to (for instance if the input contains banned content). Returns 1 if the data should be passed to the command, 0 if the data is rejected (which will terminate the running command) or -1 if an error occurred.The function arguments are as follows:
- buf
- The buffer containing user input.
- len
- The length of buf in bytes.
- log_stdout
-
int (*log_stdout)(const char *buf, unsigned int len);
The
log_stdout
() function is only used if the standard output does not correspond to a tty device. It is called whenever data can be read from the command but before it is written to the standard output. This allows the plugin to reject data if it chooses to (for instance if the output contains banned content). Returns 1 if the data should be passed to the user, 0 if the data is rejected (which will terminate the running command) or -1 if an error occurred.The function arguments are as follows:
- buf
- The buffer containing command output.
- len
- The length of buf in bytes.
- log_stderr
-
int (*log_stderr)(const char *buf, unsigned int len);
The
log_stderr
() function is only used if the standard error does not correspond to a tty device. It is called whenever data can be read from the command but before it is written to the standard error. This allows the plugin to reject data if it chooses to (for instance if the output contains banned content). Returns 1 if the data should be passed to the user, 0 if the data is rejected (which will terminate the running command) or -1 if an error occurred.The function arguments are as follows:
- buf
- The buffer containing command output.
- len
- The length of buf in bytes.
- register_hooks
- See the Policy plugin API
section for a description of
register_hooks
. - deregister_hooks
- See the Policy plugin API
section for a description of
deregister_hooks.
- change_winsize
-
int (*change_winsize)(unsigned int lines, unsigned int cols);
The
change_winsize
() function is called whenever the window size of the terminal changes from the initial values specified in theuser_info
list. It returns 1 on success, 0 on failure, -1 if an error occurred (which will terminate the running command).
Same as for the Policy plugin API.
Signal handlers¶
The sudo
front end installs default signal
handlers to trap common signals while the plugin functions are run. The
following signals are trapped by default before the command is executed:
If a fatal signal is received before the command is
executed, sudo
will call the plugin's
close
()
function with an exit status of 128 plus the value of the signal that was
received. This allows for consistent logging of commands killed by a signal
for plugins that log such information in their
close
() function. An exception to this is
SIGPIPE
, which is ignored until the command is
executed.
A plugin may temporarily install its own signal handlers but must restore the original handler before the plugin function returns.
Hook function API¶
Beginning with plugin API version 1.2, it is possible to install
hooks for certain functions called by the sudo
front
end.
Currently, the only supported hooks relate to the handling of
environment variables. Hooks can be used to intercept attempts to get, set,
or remove environment variables so that these changes can be reflected in
the version of the environment that is used to execute a command. A future
version of the API will support hooking internal
sudo
front end functions as well.
Hook structure
Hooks in sudo
are described by the
following structure:
typedef int (*sudo_hook_fn_t)(); struct sudo_hook { unsigned int hook_version; unsigned int hook_type; sudo_hook_fn_t hook_fn; void *closure; };
The sudo_hook
structure has the following
fields:
- hook_version
- The
hook_version
field should be set toSUDO_HOOK_VERSION
. - hook_type
- The
hook_type
field may be one of the following supported hook types:SUDO_HOOK_SETENV
- The C library setenv(3) function. Any registered
hooks will run before the C library implementation. The
hook_fn
field should be a function that matches the following typedef:typedef int (*sudo_hook_fn_setenv_t)(const char *name, const char *value, int overwrite, void *closure);
If the registered hook does not match the typedef the results are unspecified.
SUDO_HOOK_UNSETENV
- The C library unsetenv(3) function. Any registered
hooks will run before the C library implementation. The
hook_fn
field should be a function that matches the following typedef:typedef int (*sudo_hook_fn_unsetenv_t)(const char *name, void *closure);
SUDO_HOOK_GETENV
- The C library getenv(3) function. Any registered
hooks will run before the C library implementation. The
hook_fn
field should be a function that matches the following typedef:typedef int (*sudo_hook_fn_getenv_t)(const char *name, char **value, void *closure);
If the registered hook does not match the typedef the results are unspecified.
SUDO_HOOK_PUTENV
- The C library putenv(3) function. Any registered
hooks will run before the C library implementation. The
hook_fn
field should be a function that matches the following typedef:typedef int (*sudo_hook_fn_putenv_t)(char *string, void *closure);
If the registered hook does not match the typedef the results are unspecified.
- hook_fn
- sudo_hook_fn_t hook_fn;
The
hook_fn
field should be set to the plugin's hook implementation. The actual function arguments will vary depending on thehook_type
(seehook_type
above). In all cases, theclosure
field ofstruct sudo_hook
is passed as the last function parameter. This can be used to pass arbitrary data to the plugin's hook implementation.The function return value may be one of the following:
SUDO_HOOK_RET_ERROR
- The hook function encountered an error.
SUDO_HOOK_RET_NEXT
- The hook completed without error, go on to the next hook (including
the native implementation if applicable). For example, a
getenv(3) hook might return
SUDO_HOOK_RET_NEXT
if the specified variable was not found in the private copy of the environment. SUDO_HOOK_RET_STOP
- The hook completed without error, stop processing hooks for this
invocation. This can be used to replace the native implementation. For
example, a
setenv
hook that operates on a private copy of the environment but leavesenviron
unchanged.
Note that it is very easy to create an infinite loop when hooking C library functions. For example, a getenv(3) hook that calls the snprintf(3) function may create a loop if the snprintf(3) implementation calls getenv(3) to check the locale. To prevent this, you may wish to use a static variable in the hook function to guard against nested calls. For example:
static int in_progress = 0; /* avoid recursion */ if (in_progress) return SUDO_HOOK_RET_NEXT; in_progress = 1; ... in_progress = 0; return SUDO_HOOK_RET_STOP;
Hook API Version Macros
/* Hook API version major/minor */ #define SUDO_HOOK_VERSION_MAJOR 1 #define SUDO_HOOK_VERSION_MINOR 0 #define SUDO_HOOK_VERSION SUDO_API_MKVERSION(SUDO_HOOK_VERSION_MAJOR,\ SUDO_HOOK_VERSION_MINOR)
For getters and setters see the Policy plugin API.
Remote command execution¶
The sudo
front end does not have native
support for running remote commands. However, starting with
sudo
1.8.8, the -h
option
may be used to specify a remote host that is passed to the policy plugin. A
plugin may also accept a
runas_user
in the form of “user@hostname” which will work with older
versions of sudo
. It is anticipated that remote
commands will be supported by executing a “helper” program.
The policy plugin should setup the execution environment such that the
sudo
front end will run the helper which, in turn,
will connect to the remote host and run the command.
For example, the policy plugin could utilize
ssh
to perform remote command execution. The helper
program would be responsible for running ssh
with
the proper options to use a private key or certificate that the remote host
will accept and run a program on the remote host that would setup the
execution environment accordingly.
Note that remote sudoedit
functionality
must be handled by the policy plugin, not sudo
itself as the front end has no knowledge that a remote command is being
executed. This may be addressed in a future revision of the plugin API.
Conversation API¶
If the plugin needs to interact with the user, it may do so via
the
conversation
()
function. A plugin should not attempt to read directly from the standard
input or the user's tty (neither of which are guaranteed to exist). The
caller must include a trailing newline in msg
if one
is to be printed.
A
printf
()-style
function is also available that can be used to display informational or
error messages to the user, which is usually more convenient for simple
messages where no use input is required.
Conversation function structures
The conversation function takes as arguments pointers to the following structures:
struct sudo_conv_message { #define SUDO_CONV_PROMPT_ECHO_OFF 0x0001 /* do not echo user input */ #define SUDO_CONV_PROMPT_ECHO_ON 0x0002 /* echo user input */ #define SUDO_CONV_ERROR_MSG 0x0003 /* error message */ #define SUDO_CONV_INFO_MSG 0x0004 /* informational message */ #define SUDO_CONV_PROMPT_MASK 0x0005 /* mask user input */ #define SUDO_CONV_PROMPT_ECHO_OK 0x1000 /* flag: allow echo if no tty */ int msg_type; int timeout; const char *msg; }; #define SUDO_CONV_REPL_MAX 255 struct sudo_conv_reply { char *reply; }; typedef int (*sudo_conv_callback_fn_t)(int signo, void *closure); struct sudo_conv_callback { unsigned int version; void *closure; sudo_conv_callback_fn_t on_suspend; sudo_conv_callback_fn_t on_resume; };
Pointers to the
conversation
()
and printf
()-style functions are passed in to the
plugin's open
() function when the plugin is
initialized. The following type definitions can be used in the declaration
of the open
() function:
typedef int (*sudo_conv_t)(int num_msgs, const struct sudo_conv_message msgs[], struct sudo_conv_reply replies[], struct sudo_conv_callback *callback); typedef int (*sudo_printf_t)(int msg_type, const char *fmt, ...);
To use the
conversation
()
function, the plugin must pass an array of
sudo_conv_message
and
sudo_conv_reply
structures. There must be a
struct sudo_conv_message
and struct
sudo_conv_reply
for each message in the conversation. The
struct sudo_conv_callback
pointer, if not
NULL
, should contain function pointers to be called
when the sudo
process is suspended and/or resumed
during conversation input. The on_suspend and
on_resume functions are called with the signal that
caused sudo
to be suspended and the
closure pointer from the struct
sudo_conv_callback
. These functions should return 0 on success and -1
on error. On error, the conversation will end and the conversation function
will return a value of -1. The intended use is to allow the plugin to
release resources, such as locks, that should not be held indefinitely while
suspended and then reacquire them when the process is resumed. Note that the
functions are not actually invoked from within a signal handler.
The plugin is responsible for freeing the reply
buffer located in each struct sudo_conv_reply
, if it
is not NULL
.
SUDO_CONV_REPL_MAX
represents the maximum length of
the reply buffer (not including the trailing NUL character). In practical
terms, this is the longest password sudo
will
support. It is also useful as a maximum value for the
memset_s
()
function when clearing passwords filled in by the conversation function.
The
printf
()-style
function uses the same underlying mechanism as the
conversation
() function but only supports
SUDO_CONV_INFO_MSG
and
SUDO_CONV_ERROR_MSG
for the
msg_type
parameter. It can be more convenient than using the
conversation
() function if no user reply is needed
and supports standard printf
() escape sequences.
See the sample plugin for an example of the
conversation
()
function usage.
Sudoers group plugin API¶
The sudoers
plugin supports its own plugin
interface to allow non-Unix group lookups. This can be used to query a group
source other than the standard Unix group database. Two sample group plugins
are bundled with sudo
,
group_file
and
system_group,
are detailed in sudoers(5). Third party group plugins
include a QAS AD plugin available from Quest Software.
A group plugin must declare and populate a
sudoers_group_plugin
struct in the global scope.
This structure contains pointers to the functions that implement plugin
initialization, cleanup and group lookup.
struct sudoers_group_plugin { unsigned int version; int (*init)(int version, sudo_printf_t sudo_printf, char *const argv[]); void (*cleanup)(void); int (*query)(const char *user, const char *group, const struct passwd *pwd); };
The sudoers_group_plugin
struct has the
following fields:
- version
- The
version
field should be set to GROUP_API_VERSION.This allows
sudoers
to determine the API version the group plugin was built against. - init
-
int (*init)(int version, sudo_printf_t plugin_printf, char *const argv[]);
The
init
() function is called after sudoers has been parsed but before any policy checks. It returns 1 on success, 0 on failure (or if the plugin is not configured), and -1 if a error occurred. If an error occurs, the plugin may call theplugin_printf
() function withSUDO_CONF_ERROR_MSG
to present additional error information to the user.The function arguments are as follows:
- version
- The version passed in by
sudoers
allows the plugin to determine the major and minor version number of the group plugin API supported bysudoers
. - plugin_printf
- A pointer to a
printf
()-style function that may be used to display informational or error message to the user. Returns the number of characters printed on success and -1 on failure. - argv
- A
NULL
-terminated array of arguments generated from the group_plugin option in sudoers. If no arguments were given, argv will beNULL
.
- cleanup
-
void (*cleanup)();
The
cleanup
() function is called whensudoers
has finished its group checks. The plugin should free any memory it has allocated and close open file handles. - query
-
int (*query)(const char *user, const char *group, const struct passwd *pwd);
The
query
() function is used to ask the group plugin whether user is a member of group.The function arguments are as follows:
- user
- The name of the user being looked up in the external group database.
- group
- The name of the group being queried.
- pwd
- The password database entry for user, if any. If
user is not present in the password database,
pwd will be
NULL
.
/* Sudoers group plugin version major/minor */ #define GROUP_API_VERSION_MAJOR 1 #define GROUP_API_VERSION_MINOR 0 #define GROUP_API_VERSION ((GROUP_API_VERSION_MAJOR << 16) | \ GROUP_API_VERSION_MINOR)
PLUGIN API CHANGELOG¶
The following revisions have been made to the Sudo Plugin API.
- Version 1.0
- Initial API version.
- Version 1.1 (sudo 1.8.0)
- The I/O logging plugin's
open
() function was modified to take thecommand_info
list as an argument. - Version 1.2 (sudo 1.8.5)
- The Policy and I/O logging plugins'
open
() functions are now passed a list of plugin parameters if any are specified in sudo.conf(5).A simple hooks API has been introduced to allow plugins to hook in to the system's environment handling functions.
The
init_session
Policy plugin function is now passed a pointer to the user environment which can be updated as needed. This can be used to merge in environment variables stored in the PAM handle before a command is run. - Version 1.3 (sudo 1.8.7)
- Support for the exec_background entry has been added to
the
command_info
list.The max_groups and plugin_dir entries were added to the
settings
list.The
version
() andclose
() functions are now optional. Previously, a missingversion
() orclose
() function would result in a crash. If no policy pluginclose
() function is defined, a defaultclose
() function will be provided by thesudo
front end that displays a warning if the command could not be executed.The
sudo
front end now installs default signal handlers to trap common signals while the plugin functions are run. - Version 1.4 (sudo 1.8.8)
- The
remote_host
entry was added to the
settings
list. - Version 1.5 (sudo 1.8.9)
- The
preserve_fds
entry was added to the
command_info
list. - Version 1.6 (sudo 1.8.11)
- The behavior when an I/O logging plugin returns an error (-1) has changed.
Previously, the
sudo
front end took no action when thelog_ttyin
(),log_ttyout
(),log_stdin
(),log_stdout
(), orlog_stderr
() function returned an error.The behavior when an I/O logging plugin returns 0 has changed. Previously, output from the command would be displayed to the terminal even if an output logging function returned 0.
- Version 1.7 (sudo 1.8.12)
- The
plugin_path
entry was added to the
settings
list.The debug_flags entry now starts with a debug file path name and may occur multiple times if there are multiple plugin-specific Debug lines in the sudo.conf(5) file.
- Version 1.8 (sudo 1.8.15)
- The sudoedit_checkdir and
sudoedit_follow entries were added to the
command_info
list. The default value of sudoedit_checkdir was changed to true in sudo 1.8.16.The sudo conversation function now takes a pointer to a
struct sudo_conv_callback
as its fourth argument. Thesudo_conv_t
definition has been updated to match. The plugin must specify that it supports plugin API version 1.8 or higher to receive a conversation function pointer that supports this argument. - Version 1.9 (sudo 1.8.16)
- The execfd entry
was added to the
command_info
list. - Version 1.10 (sudo 1.8.19)
- The umask entry
was added to the
user_info
list. The iolog_group, iolog_mode, and iolog_user entries were added to thecommand_info
list. - Version 1.11 (sudo 1.8.20)
- The timeout entry was added to the
settings
list. - Version 1.12 (sudo 1.8.21)
- The
change_winsize
field was added to the io_plugin struct.
SEE ALSO¶
AUTHORS¶
Many people have worked on sudo
over the
years; this version consists of code written primarily by:
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.
March 21, 2018 | Sudo 1.8.23 |