dear devuaneers, suckless hackers and friends of simplicity In the past days we are working hard on Devuan, but also on our dyne.org project Dowse whose prototype is based on an RPi version of Devuan.
Thinkering on the security model in Dowse and other projects, parazyd found the 'sup' tool to be ideal: originally written by the good folks at suckless.org, its minimalist approach to privilege escalation is enlightening in its simplicity. Basically sup is an hard-coded sudo. I adopted the software (wrote a mail to pancake, pending response) and proceeded improving some things: added musl-libc production build capability to defend the binary from LD_SO_PRELOAD attacks and also added the optional sha256 hash check of binary files. in the hope it will be useful, sup is available here (LGPLv3) https://git.devuan.org/jaromil/sup to stay up to date with future releases, one can also keep an eye here http://freshcode.club/projects/sup and for those who prefer github is mirrored also here https://github.com/dyne/sup here below I paste the README, happy hacking ----- # sup ## a "small is beautiful" tool for UNIX privilege escalation 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. the latest version of sup can be found on https://git.devuan.org/jaromil/sup and on its mirrors at dyne.org and github.com. ## why are you whispering? 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 [http://www.musl-libc.org/](musl-libc) and hardcoded sha256 hashing of binary files. ## configure sup's configuration resides in config.h and should be set before building. here below an intuitive example ```c #define USER 1000 #define GROUP -1 #define SETUID 0 #define SETGID 0 #define CHROOT "" #define CHRDIR "" #define HASH 1 #define ENFORCE 1 static struct rule_t rules[] = { // allow user to run these programs when found in 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 in PATH with matching hash { USER, GROUP, "id", "*", "db533b77fc9e262209a46e0f.." }, // allow to run any program found in PATH { USER, GROUP, "*", "*"}, { 0 }, // end of configuration }; ``` Fields are organized as following: | UID | GUID | binary name | binary path | hash (optional) | - `UID` is the numeric id which must own the binary for authorized execution - `GID` is the numeric group id which must own the binary for authorized execution (can be -1 for none) - `hash` can be computed before build using sha256sum (GNU coreutils) using `sup -l` the configuration can be displayed at runtime. ## build 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 and then using the `make musl` command. ## technical details sup consists of 3 files: sup.c is the main source and config.h is the configuration, hardcoded at compile time. sha256.c is optional and provides the hashing functionality if the define HASH is set. sup is written in ANSI C with POSIX1.b compliancy for GNU/Linux and BSD systems. it uses `setuid/gid` for privilege escalation and `execv()` to launch processes as superuser. ## licensing 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 Devine ``` -- Denis Roio aka Jaromil http://Dyne.org think &do tank CTO and co-founder free/open source developer 加密 6113 D89C A825 C5CE DD02 C872 73B3 5DA5 4ACB 7D10 _______________________________________________ Dng mailing list Dng@lists.dyne.org https://mailinglists.dyne.org/cgi-bin/mailman/listinfo/dng
