as_root - an ultra-minimalist alternative to sudo

About as_root

as_root is an ultra-minimalist alternative to sudo.

as_root's command line interface differs from sudo. For example, to use run shutdown -h now via sudo, you would run the command:

$  sudo  shutdown  -h  now

Whereas with as_root, you simply run the command:

$  shutdown  -h  now

In other words, you don't need to type as_root. This is possible because you install as_root as follows:

$  musl-gcc  -static  as_root.c  -o /tmp/as_root
$  sudo  mkdir  /usr/as_root                         #  You may use some other directory, if you prefer.
$  sudo  cp  /tmp/as_root  /usr/as_root/as_root
$  sudo  chown  root:$GROUP  /usr/as_root/as_root    #  Users in $GROUP will be able to run as_root.
$  sudo  chmod  450  /usr/as_root/as_root            #  Make as_root group-executable. 
$  sudo  chmod  u+s  /usr/as_root/as_root            #  Set the set-user-id bit.
$  sudo  ln  -s  as_root  /usr/as_root/shutdown      #  Create symlinks pointing to as_root.

Then you would add /usr/as_root to your PATH before other directories.

Consequently, when you run shutdown -h now, it is /usr/as_root/as_root that runs.

as_root will check if its argv matches one of the patterns specified in the ALLOW global variable.

If argv matches an ALLOW pattern, then as_root will execv() the command with elevated privileges.

If argv matches none of the ALLOW patterns, then as_root will drop privileges and still execv() the command with normal privileges. (This, too, is different from sudo.)

I wrote as_root because btrfs (and other commands) provide status information about the system. I wanted to access this status information as a non-root user. In other words, I typically use as_root to access status information, and not to make changes to the system.

Patterns are stored in the ALLOW string. The ALLOW string is compiled into as_root. There is no configuration file.

Patterns are separated by the newline character ('\n'). Arguments within a patteren are separated by one or more spaces (' ').

There are three special arguments that may be used in a pattern:

• ARG will match any one argument.
• PLUS will match one or more arguments.
• STAR will match zero or more arguments.

A single PLUS or STAR should be used only at the end of a pattern. (Using a PLUS or STAR in the middle of a pattern is not supported and will result in silent false positive pattern matches.)