sonic-buildimage/files/image_config/ssh/sshd-clear-denied-sessions

#!/usr/bin/env python

"""
This utility will find the ip addresses of all hosts that have connected to
this device via ssh, then validate they are still in the list of allowed prefixes,
and if not kill the ssh session with a SIGHUP.
"""

import os
import re
import subprocess

# Run utmpdump, capture and return its output
def run_utmpdump(_utmpFilename):
    devnull = file("/dev/null", "w" )
    p = subprocess.Popen(args=["utmpdump", _utmpFilename], stdout=subprocess.PIPE, stderr=devnull)
    (stdout, stderr) = p.communicate()
    rc = p.returncode
    assert rc is not None # because p.communicate() should wait.
    out = (stdout or '') + (stderr or '')
    if rc:
        e = SystemCommandError("%r: error code %d" % (" ".join(argv), rc))
        e.error = rc
        e.output = out
        raise e
    return stdout

# Run utmpdump and parse its output into a list of dicts and return that
def get_utmp_data(utmpFileName=None):
    """Reads the specified utmp file.
    Returns a list of dictionaries, one for each utmp entry.
    All dictionary keys and values are strings
    Values are right padded with spaces and may contain all
    spaces if that utmp field is empty.
    Dictionary keys:
        "type":     See UTMP_TYPE_* above
        "pid":      Process ID as a string
        "tty":      TTY (line) name - device name of tty w/o "/dev/"
        "tty4":     4 char abbreivated TTY (line) name
        "user":     User ID
        "host":     Hostname for remote login,
                    kernel release for Run Level and Boot Time
        "ipAddr":   IP Address
        "time":     Time and date entry was made
    See linux docs on utmp and utmpdemp for more info.
    Example output from utmpdump:
          pid     tty4   user       tty            host          ipAddr            time
      [7] [22953] [/238] [myname  ] [pts/238     ] [example.com] [253.122.98.159 ] [Mon Dec 18 21:08:09 2017 PST]
    """
    if not utmpFileName:
        utmpFileName = os.environ.get( "DEFAULT_UTMP_FILE", "/var/run/utmp" )
    if not os.path.exists(utmpFileName):
        return []
    output = run_utmpdump(utmpFileName)
    lines  = re.split("\n", output)
    regExp = re.compile(
        r"\[(?P<type>"   r"[^\]]*?)\s*\] \[(?P<pid>"  r"[^\]]*?)\s*\] " \
        r"\[(?P<tty4>"   r"[^\]]*?)\s*\] \[(?P<user>" r"[^\]]*?)\s*\] " \
        r"\[(?P<tty>"    r"[^\]]*?)\s*\] \[(?P<host>" r"[^\]]*?)\s*\] " \
        r"\[(?P<ipAddr>" r"[^\]]*?)\s*\] \[(?P<time>" r"[^\]]*?)\s*\]"  )
    entries = []
    for line in lines:
        m = regExp.match(line)
        if not m:
            # Skip header and any other lines we don't recognize
            continue
        entry = m.groupdict()
        entries.append(entry)
    return entries

# Find the source ip addresses of all ssh sessions, verify they are still allowed, and if not kill the ssh session
if __name__ == '__main__':
    for e in get_utmp_data():
        if e["host"] and e["ipAddr"] != "0.0.0.0": # entry is for a live connection
            # check allowness
            r = os.system('tcpdmatch sshd %s | grep "access.*granted" > /dev/null' % e["ipAddr"])
            # print some debugs
            print "From:", e["ipAddr"], "ssh pid:", e["pid"], "allowed" if r == 0 else "denied"
            # if needed go for the kill
            if r != 0:
                os.system("kill -1 %s" % e["pid"])