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access -- authenticator for Unix systems.
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This is access - authenticator for Unix systems and powerful privilege separator, privilege manager and privilege automation tool. The aim of access is to extend authentication options on classic and modern Unix and Unix-like systems as well as to ease switching of privileges between users, separate the roles and limit untrusted users to only permitted commands. It's like well-known sudo, but access extends the original idea behind it, as well as fixes some fatal flaws which were in original sudo. FEATURES access has many features which make it unique. Below is a short overview list. - aims to be very portable, even to legacy and crippled systems, - can run on systems where no password database is defined or present, - uses simple hierarchical rule system akin iptables one: rules parsed as they specified, from top to bottom, in one single pass, - offers possibilities to specify all Unix credentials beyond simple uid:gid pair, - rules are very precise about both invoker and target users identities: privileges can be specified down to single gid marker present/absent in grouplist, - offers possibility to specify arbitrary environment variables, and to reset them back, - offers possibilities to set working directory, chroot directory, - offers possibility to log everything required to trace the invoker, - offers possibility to lock only to one program invocation per single uid, so brute force is made impossible at all, - logging can be disabled per rule, both failed attempts and successful ones separately, - logging is possible to separate file or to syslog, if supported by platform, - it is possible to match patterns either with basic fnmatch, with extended regular expressions or simple case sensitive strings comparison. - passwords can be asked for: invoker user itself, destination user, superuser, per rule defined hash or not asked (bypass password asking) at all, - very precise about environment inside which the target program runs, - always obeys superuser: superuser is an exempt in access, - may detach current tty from target program on systems which support injecting arbitrary characters (including CR/NL) into current terminal session, so TIOCSTI tty ioctl attacks will not be possible. - offers possibility to run an external program which "audits" the invoker intent and judges about it, altering access's own decision, - offers possibility to run an external password asking program: a GUI dialog or text mode one, - offers a separate setuid server to support setuid crippled systems like android, - gives users ability to discover other users public credentials with embedded commands, - customised password prompts and deny messages, - setting environment variables from config file per rule or multiple rules, - offers an embedded password testers to verify users passwords, - offers an embedded tool to generate password hashes, - offers a basic su(1) embedded implementation, - can be configured to emulate su(1) transparently, and freely supports BSD "wheel" group, - provides a base of portable and well tested code: tf1024, getpasswd, various standard safe function wrappers, - can be readily used as a sudo(8) replacement, yet both are completely incompatible ... - was tested and ported to: Linux, Free/Net/OpenBSD, OS X, Solaris, Haiku, Syllable, Ancient C89 Linux, Android, Raspberry PI, MIPS Linux routers and more, ... and many more, because the full list will be too long for this document. INSTALLATION Installation should be simple. You need to look into Makefile and config.h and make sure that options for your platform are correct. You may also need to edit port.h header file, or directly alter some definitions in access.h header file to match your taste and needs. You will need a C compiler installed. Your C compiler must support C89 language constructs, or better. Usually, modern systems have a gcc C compiler. access development is also done using gcc compiler, although older version. You will need a GNU make. Version 3.81 was used. Older could also work, but this is untested. Then just run % make , wait for process to complete. To install access binary, run # make install as superuser, or copy result "access" executable to any place you want, then give it setuid bit: # chmod u+s /path/to/access Note that "make install" sets this bit automatically for you. It is recommended that you will give access setuid bit. Others mechanisms like Linux file system capabilities can also work, but they too limited and ugly. Author will never recommend them. access does not test, report or refuse to run nor detect "special cases", or "untrusted systems". In fact, access does not care about target operating system or platform. If it was compiled successfully, then it will probably work. access only assumes that provided runtime environment is POSIX compatible. access only tries to detect a special permissions on it's config file. access also assumes at least POSIX.1-2001 and C99 compatibility of runtime environment. Optionally it can be ported to pure old C89 systems, or "impaired" systems with incomplete or broken standard conformance, such as android, with help of included "ports". CONFIGURATION access does not require any configuration if it will be run only by superuser. But to be sure that no privileges are being hijacked, ensure creating an empty /etc/access.conf file owned by 0:0 and mode 0600, or remove a setuid bit from access binary. To configure access in a multiuser environment for usage by multiple users, please read included "access.conf.5" manual page, or it's text variant. To see command line options accepted by access, run it with "-h", or read included "access.8" manual page (or it's text variant). PROTECTION Installing access binary as world setuid executable is sufficient. You should not make it readable by anyone other than superuser. However, you can further limit access to the tool by creating a special group, for example, named "access", then running these commands: # chown 0:access /path/to/access # chmod 4710 /path/to/access (do not exit superuser shell until you will test you can get back in another tty) Since that, only users belonging to "access" group able to run access itself, and then only access will authenticate them, if told to. I recommend this approach on desktop systems, but with only change that, instead of creating a special group, one can set group to the main system user's primary group. access tries to detect that it's config file is well protected. It checks it for readability by other users and ensures that only superuser has access to this file and this file is owned by superuser. However access cannot detect that it's binary file is well protected too, because there is no portable way of finding a binary for itself. When logging to file, access ensures that log file is protected, so only superuser can read it. SEE ALSO The main documentation for this program is stored in "access.8" and "access.conf.5" manual pages. AUTHORS access was written by Andrey Rys (firstname.lastname@example.org). LICENSE MIT/X11 permissive. See COPYRIGHT file. DISCLAIMER This tool is a _proof of concept_. It does not claim security bug cleanliness. You take full responsibility by using it, not the authors of the tool. There is NO WARRANTY of any kind for this program, it's parts or derivatives.