sup
is a very small and secure c application. it is designed to run as
root (with suid bit on) to facilitate the privilege escalation of users
to execute certain programs as superuser.
all settings in sup are hard-coded at compile time. sup is very
portable and self-contained, designed for production use as a static
binary. sup is a sort of hard-coded sudo
: it is an ideal companion
for artisans building small containers and embedded systems.
sup’s new homepage is sup.dyne.org
sup code can be read and reviewed on-line
stable releases can be downloaded from files.dyne.org/sup
releases are signed with the maintainer’s keys
the develpment version of sup can be found at git.devuan.org/jaromil/sup
of course there is also a github mirror
as you may have realised already, sup is so minimal that all its documentation is written lowercase. it was originally written in 2009 by pancake of nopcode.org and maintained until 2011 as part of the suckless tools. in 2016 sup is being adopted by jaromil of dyne.org, extending its features to support static build with musl-libc and hardcoded sha256 hashing of binary files.
sup’s configuration resides in config.h
and should be set before
building. here below an intuitive example:
// sup's configuration file
// need sup to be re-compiled for any change to be effective
/// un/comment flags below to remove functionalities
#define HASH 1
#define DAEMON 1
// #define DEBUG 1
#ifndef FLAGSONLY
#define USER 1000
#define GROUP -1
#define SETUID 0
#define SETGID 0
#define CHROOT ""
#define CHRDIR ""
static struct rule_t rules[] = {
// allow user to run these programs when found at a specific path location
{ USER, GROUP, "whoami", "/usr/bin/whoami", "" },
{ USER, GROUP, "ifconfig", "/sbin/ifconfig", "" },
{ USER, GROUP, "ls", "/bin/ls", "" },
{ USER, GROUP, "wifi", "/root/wifi.sh", "" },
// allow to run id when found with matching hash anywhere in PATH
{ USER, GROUP, "id", "*", "db533b77fc9e262209a46e0f.." },
// allow to run any program found in PATH
{ USER, GROUP, "*", "*"},
{ 0 }, // end of configuration
};
#endif
fields are organized as follows:
| USER | GROUP | binary name | binary path | hash (optional) |
USER
is the numeric id (UID) of the user authorized to execute the
binary as superuserGROUP
is the numeric group (GID) of the user authorized to execute
the binary as superuser (use -1 for none)binary name
is the command to run with setuid/setgid
, e.g., ls
binary path
is the path to the program, e.g., /bin/ls
hash
can be computed before build using sha256sum
(from GNU coreutils)binary name
and binary path
accept the wildcard character *
to
mean any executable, and anywhere in PATH, respectively.
running sup -l
will display the compiled-in configuration.
sup requires a c compiler and the gnu make tool to be built.
a simple make
command will build a sup binary good enough for
evaluation purposes, with dynamic links to the libm
and libc
libraries installed system-wide.
for production use, sup should be built as a static binary: this is
easily done by first installing musl-libc
in its default location
(/usr/local/musl
) and then using the make musl
command inside sup.
sup consists of 3 files:
sup.c
is the main sourceconfig.h
is the configuration, hardcoded at compile timesha256.c
is optional and provides the hashing functionality if
# define HASH 1
is set.sup is written in ansi c with posix1.b compliance for gnu/linux and
bsd systems. it uses setuid/gid
for privilege escalation and
execv()
to launch processes as superuser. daemon mode uses fork()
to send processes in the background with NOTTY
and stdin/out/err
file descriptors set to /dev/null
.
it does not make sense to have a sup package. sup is configured at build-time and its built binaries are specific to the task they have been built and set suid for. sup is a tool for people distributing containers, online services, embedded devices, and such.
sup is different from doas
, because doas
is
configured at runtime.
same reason as above, sudo
is configured at runtime.
sup is made so that people (or scripts) don’t have to type passwords
every time they need to execute something they are entitled to execute
as superusers. with su
one has to type the root password every time.
also scripts won’t work without interaction.
this new code hasn’t been grinded by the merry folks at suckless yet, but pancake has acknowledged this development and, having left maintainance, is happy to hand it over to jaromil.
sup is copyleft software licensed as gnu lesser public license (lgplv3). when compiled with hashing capability, its license turns into gnu gplv2+ because of the sha256 component.
sup is copyleft (c) 2009-2011 by pancake of nopcode.org
. (c) 2016 by jaromil of dyne.org
the fips-180-2 sha-256 implementation optionally included in sup is
copyleft (c) 2001-2003 by christophe cevine