Practical (closer to the classical Linux one) way to use (automate) SUDO for CygWin

Question

Being able to use sudo commands in CygWin is useful, and faster than opening an elevated shell:

Luis@Kenobi /cygdrive/c/Users/Luis
$ net user /add TestUser
System error 5.
Access denied.

Luis@Kenobi /cygdrive/c/Users/Luis
$ sudo net user /add TestUser
Command completed successfully.

As shown above, you can run Windows commands/scripts too, just as Linux. For me is neat; works on remote (SSH) consoles and allows to combine Windows/Linux commands. So being able to execute administrative tasks is nearly a must.

But the SUDO for CygWin project has a behavior that could be dangerous: it works as a server/client architecture, in fact, a client (sudo) send requests of commands to a server (sudoserver.py) at internal (not listening outside the local computer) port 7070TCP, with no user or permissions checking, so anyone (even unprivileged users) logged in onto the computer could execute admins (CygWin or Windows) shell commands or scripts (CygWin or Windows, too).
The problem gets worse if you keep the suggested method of the author: registering "sudoserver.py" as a service, so it will keep permanently running.

So, to maintain the things a bit more secure (not totally), I do:
1.- Execute "sudoserver.py" on an admin shell.
2.- Execute my "sudo" commands on another CygWin shell.
3.- Close (Ctrl+C) "sudoserver.py" and the admin shell.

A bit annoying. I am workarounding it using a .cmd file with assigned hotkey that runs "sudoserver.py", and I am closing (manually) it after my administrative jobs, but still far from the classic "sudo" usability on Linux.

The great and practical way would be some method that:

1. **Auto-opens "sudoserver.py" requesting for UAC Elevation Prompt (or user/password).
2. Closes it after a while, so UAC requestion will not keep disturbing in case of several sudo commands executed sequentially.

Is there any way to automate this, at least partially?

Answer 1

NOTE: This is mostly a program (shell script) I made, and I know this forum is more a question-answer site than a programs-introduction one. But I don't have any GitHub (or similar) account, nor have I had the time to research about the method of publishing an Open Source program to the community. So, as long as there is a risk that a working and useful program keeps unnoticed (even for months) to those who could enjoy it, and it would be sad to not share an already made program, I am going to publish it here for now. No problems for me if it the admins decide to remove this thread, I will understand. I hope to have worded the matter in a question-answer way enough to make it useful to this forum. If there are enough interested users, I will do my best to dedicate some time to continue the project (after all my researchs, I have not found anything closest to this on Internet, but, well... I don't know if my script is valuable or it has been a waste of time).

I have programmed a simple Linux shell script that works (until now) on CygWin and helps (I hope) reducing the SUDO for CygWin time-attack interval. The program is named TOUACExt (acronym of "TimeOut and UAC Extension") and acts as a wrapper for SUDO for CygWin (required installed), and is really composed by a set of four .sh programs.

Features:

• Comfortable usage: By simulating the original sudo from Linux behavior, the UAC confirmation request prompt only appears once (multiple consecutive sudo commands will only generate one UAC request). As long as sudoserver.py keeps running (15 minutes default), there will be no more UAC requests.
• Privileged (Admin) users only get UAC confirmation request (Yes/No) on screen.
• Unprivileged (non-Admin) users get an Administrator account/password input screen.
• sudoserver.py keeps running, then closes automatically after predefined time (15 minutes) from the last sudo command execution.
• sudoserver.py does not close (keeps runing and will check again in 5 minutes) in case of any instance of sudo running.
• Works remotely (tested via SSH):
  • Unprivileged users can not start sudoserver.py remotely.
• Creates a (yet simple and not very readable) log at /var/log/SUDOForCygWin/.

Requirements (in CygWin):

• SUDO for CygWin.
• pgrep (at procps package).
• flock (at util-linux package).
• nohup (I think installed by default on CygWin, but not sure).

Assuming: - The two programs of the SUDO for CygWin project on the path suggested by the author:

/usr/local/bin/sudoserver.py
/usr/local/bin/sudo

TOUACExt have been tested working on Windows 7 SP1 and Windows XP SP3, but I don't know if it makes sense in using it on this last one.

Installation Instructions:

• Put this script (suggested name: SUDOServer.cmd) and create a shortcut (you can personalize its icon if you want) to it named SUDOServer.lnk (you must enable on this shortcut Advanced Options --> Execute as Administrator) anywhere on your Windows path, so sudoserver.py can be directly requested from Windows:

  c:\CygWin\bin\python2.7.exe /usr/local/bin/sudoserver.py

• Put the four .sh scripts of TOUACExt on the path, for example:

  /usr/local/bin/SUDO.sh /usr/local/bin/SUDOServer.sh /usr/local/bin/SUDOServerWatchDog.sh /usr/local/bin/SUDOServerWatchDogScheduler.sh

• Rename the original Python script from sudo to sudo.py:

  mv /usr/local/bin/sudo /usr/local/bin/sudo.py
  WARNING: The original "sudo" Python script must not remain anywhere in your path, or it could be executed instead.

• Create this alias (for example, manually or by editing your ~/.bashrc):

  alias sudo='SUDO.sh'

Code for SUDO.sh:

#!/bin/bash

# ********** SUDO.sh v0.04a **********

# Variables:
# LockFile (will use a temporal one for now):
#lockfile=sudoserver-running.lck
LockFile=lockfile.lck

# Creating LogFile (if it does not exist):
mkdir /var/log/SUDOForCygWin 2>/dev/null
chmod 777 /var/log/SUDOForCygWin 2>/dev/null
LogFile=/var/log/SUDOForCygWin/$(date +%Y%m%d).log
exec 5>>$LogFile    # Redirector 5 will be the log file.
chmod 777 $LogFile >&5 2>&5 # Writable to anyone (for now).

# Start of the program
echo "========== Starting SUDO Server for CygWin ==========" >&5
echo $(date) >&5

# does the lock file exists as locked?
if [ $(flock -n $TMP/$LockFile echo>/dev/null;echo $?) -eq 0 ]
   then
    # The lock file is not locked.
    echo "LockFile not locked. Testing sudo access..." >&5
    if [ $(sudo.py vartemp=0>/dev/null 2>/dev/null;printf $?) -eq 0 ]
       then
        # Wooops. sudoserver.py is running without the lockfile. Better to correct this.
        echo "LockFile not locked, but sudoserver.py seems to be running." >&5
        printf "Killing sudoserver.py...\n" >&5
        sudo.py kill $(sudo.py pgrep.exe -f -l sudoserver.p[y] | grep "pgrep" -v | awk '{print $1}') >&5 2>&5
    fi
    # Starting SUDOServer.sh
    printf "Requesting SUDOServer start...\n" >&5
    nohup SUDOServer.sh >&5 2>&1&
    # Wait some time delay for UAC Prompt to start
    sleep 2
    timeout=$((SECONDS+10))
    # Has sudoserver.py already started?
    while [ $(flock -w 1 $TMP/$LockFile echo>/dev/null;printf $?) -eq 0 ] || [ $(tasklist | grep "consent.exe" -i>/dev/null;printf $?) -eq 0 ]
    do
        # No. We have to wait.
        # Waiting for SUDOServer.py to be running.
        printf "."
        if [ $SECONDS -ge $timeout ]
           then
            # sudoserver.py not responding. Aborting with errorlevel=3.
            printf "sudoserver.py not responding. Aborting.\n"
            exit 3
        fi
    done
    # Yes. sudoserver.py is up and running.
fi

printf "\n"
# Schedule (add) SUDOServer Watch Dog to Task Scheduler:
SUDOServerWatchDogScheduler.sh

# Invoke requested sudo command
sudo.py $@

#printf "ErrorLevel was: "$?


# ErrorLevel Codes:
# 3 --> timeout waiting for sudoserver.py to respond.

Code for SUDOServer.sh:

#!/bin/bash

# ********** SUDOServer.sh v0.04a **********

# Variables:
# LockFile (a temporal one for now):
#lockfile=sudoserver-running.lck
LockFile=lockfile.lck

# Check for other instances of sudoserver.py running
if [ $(flock -n $TMP/$LockFile echo>/dev/null;printf $?) -eq 0 ]
   then
    printf "Creating lockfile: "$TMP/$LockFile"\n"
    flock $TMP/$LockFile -c 'cmd /c SUDOServer'
    # The file has been unlocked. Send error level=2.
    exit 2
   else
    printf "The lockfile: "$TMP/$LockFile" is locked by another process.\n"
    printf "Exiting SUDOServer.sh"
fi

printf "SUDOServer.sh execution finished. Exiting."

# Exiting with no problems.
exit 0

# ErrorLevel Codes:
# 2 --> SUDOServer.lnk (maybe denial of UAC). 

Code for SUDOServerWatchDog.sh:

#!/bin/bash

# ********** SUDOServerWatchDog.sh v0.04a **********

# Variables:
# LockFile (a temporal one for now):
#lockfile=sudoserver-running.lck
LockFile=lockfile.lck

# Redirecting to LogFile:
LogFile=/var/log/SUDOForCygWin/$(date +%Y%m%d).log
exec 5>>$LogFile
if [ $(stat $LogFile -c %a) -ne 777 ]
   then
    echo "Logfile "$LogFile" has incorrect permissions." >&5
    echo "Attemping to change permissions of "$LogFile >&5
    chmod 777 $LogFile >&5 2>&5
fi

# Remove Task Scheduler entry, if exists.
if [ $(schtasks.exe /query | grep "SUDOServerWatchDog" -i>/dev/null 2>&5;printf $?) -eq 0 ]
   then
    sudo.py schtasks.exe /delete /tn "SUDOServerWatchDog" /f >&5 2>&5
fi

# Is sudoserver.py running?
if [ $(flock -n $TMP/$LockFile echo>/dev/null;printf $?) -eq 1 ] || [ $(sudo.py vartemp=0>/dev/null 2>/dev/null;printf $?) -eq 0 ]
   then
    # Yes. sudoserver.py is running. So...
    printf "sudoserver.py detected running...\n" >&5
    # Is any instance of sudo running right now?
    if [ $(sudo.py pgrep -f -l "/usr/local/bin/sudo.py " | grep -v grep>/dev/null 2>&5;printf $?) -eq 0 ]
       then
        # Yes. sudo is running right now. So...
        printf "There are instances of sudo running.\n" >&5
        sudo.py schtasks /create /tn "SUDOServerWatchDog" /tr "SUDOServerWatchDog" /sc minute /mo 5 /sd 10/10/2010 /ru "SYSTEM" >&5 2>&5
        printf "Will check again in 5 minutes. Adding Task.\n" >&5
       else
        # No. sudo is not running right now. So...
        # Kill sudoserver.py.
        printf "Closing sudoserver.py\n" >&5
        sudo.py kill $(sudo.py pgrep.exe -f -l sudoserver.p[y] | grep "pgrep" -v | awk '{print $1}')
    fi
   else
    printf "sudoserver.py not running. Nothing to be done.\n" >&5
fi 

Code for SUDOServerWatchDogScheduler.sh:

#!/bin/bash

# ********** SUDOWatchDogScheduler.sh v0.04a **********

# Check if WatchDog is already scheduled
if [ $(schtasks.exe /query | grep "SUDOServerWatchDog">/dev/null 2>&5;printf $?) -eq 0 ]
   then
    # Yes. Remove it in order to create a new one.
        echo "Task SUDOServerWatchDog already existing." >&5
    echo "Removing task SUDOServerWatchDog..." >&5
    sudo.py schtasks.exe /delete /tn "SUDOServerWatchDog" /f >&5 2>&5
    if [ $? -eq 0 ]
       then
        # Task correctly deleted.
        echo "Task correctly removed." >&5
       else
        # Something failed in task creation. Report.
        echo "ERROR on deleting the SUDOServerWatchDog programmed task." >&5
    fi
fi
# Schedule new task for deletion.
echo "Adding new SUDOServerWatchDog task to trigger in 15 minutes." >&5
sudo.py schtasks /create /tn "SUDOServerWatchDog" /tr "SUDOServerWatchDog" /sc minute /mo 15 /sd 10/10/2010 /ru "SYSTEM" >&5 2>&5
if [ $? -eq 0 ]
   then
    # Task correctly scheduled.
    echo "Task SUDOServerWatchDog correctly scheduled." >&5
   else
    # Something failed in task scheduling. Report.
    echo "ERROR on scheduling programmed task SUDOServerWatchDog." >&5
fi 

Test the program from a CygWin Bash shell:

Luis@Kenobi ~
$ sudo ls -la
<UAC ELEVATION PROMPT APPEARS>
total 49
drwxr-xr-x+ 1 Luis  None     0 abr  7 02:23 .
drwxrwxrwt+ 1 Luis- None     0 abr  4 03:27 ..
-rw-------  1 Luis  None 13798 abr 14 00:31 .bash_history
-rwxr-xr-x  1 Luis  None  1494 mar  3 11:36 .bash_profile
-rwxr-xr-x  1 Luis  None  6260 abr  6 05:19 .bashrc
-rwxr-xr-x  1 Luis  None  1919 mar  3 11:36 .inputrc
-rw-------  1 Luis  None    35 abr  2 01:43 .lesshst
-rwxr-xr-x  1 Luis  None  1236 mar  3 11:36 .profile
drwx------+ 1 Luis  None     0 mar  8 01:49 .ssh
-rw-r--r--  1 Luis  None     7 mar  4 18:01 d:ppp.txt
-rw-r--r--  1 Luis  None    37 abr  7 02:23 my.log

NOTE2: These scripts are in pre-beta release, so they are still buggy and the code is not very clean. Anyway, in my tests with three different Windows 7 computers they seem to be working (mostly) OK.

Brief explanation of the program:

1. Due to the alias, when performing a sudo command the SUDO.sh script is invoked.
2. SUDO.sh calls SUDOServer.sh, opening (via SUDOServer.lnk) "sudoserver.py" if needed.
3. The original sudo command invoked by the user is executed.
4. Then SUDO.sh calls SUDOServerWatchDogScheduler.sh, that schedules SUDOServerWatchDog.sh for execution after the given time (15 minutes default) to close sudoserver.py.
5. After the predefined time, SUDOServerWatchDog.sh closes sudoserver.py. If there are any instance of sudo running, it programs itself for new execution after 5 minutes.

To Do:

• Self installer that creates all the .sh, .cmd and .lnk files automatically.
• Establish lock file to some other (it is at $TMP/lockfile.lck).
• Add a configuration script or .config file (for defaults in timeouts, file locations... etc).
• Add System account behavior (thanks, @Wyatt8740).
• ¿Change "flock" (internal locking SUDO mode) with "fuser" where appropriate?
• Suggestions accepted.

Reported Bugs:

• The bash shell keeps open even after inputing exit if sudoserver.py is running until it closes. Provisional workarounds are welcome.

I hope someone will use the long hours programming I have dedicated to TOUACExt.
Enhancements and corrections accepted.
Suggestions about where should I go publishing the code to stop nagging this forum accepted too ;-) .

Sorry for the long post. I don't have much free time, and this project was about disappear on my closet (maybe for years, who knows?).

Answer 2

SIMPLE sudo.bat (uses nircmd)

Nircmd can be downloaded here:
http://www.nirsoft.net/utils/nircmd.html

I downloaded nircmd and renamed nircmdc.exe to nircmd.exe, replacing the original nircmd.exe. I then moved it to C:\windows\system32.

I also made the following batch file to allow arguments to be passed to the script.

It should be said that I have disabled UAC on my machine, so I no longer need this script, but it DOES work as of windows 8. It works in cygwin just as well.

@echo off
if "%*" == "" goto error
nircmd elevate %*
goto thisiseof
:error
echo No arguments were given. Exiting.
:thisiseof

Answer 3

Being unhappy with the available solution, I adopted nu774's script to add security and make it easier to setup and use. The project is available on Github

To use it, just download cygwin-sudo.py and run it via python3 cygwin-sudo.py **yourcommand**.

You can set up an alias for convenience:

alias sudo="python3 /path-to-cygwin-sudo/cygwin-sudo.py"