Mini Shell

"""
Watch the shell commands being executed actively. This beacon requires strace.
"""

import logging
import time

import salt.utils.path
import salt.utils.stringutils
import salt.utils.vt

__virtualname__ = "sh"

log = logging.getLogger(__name__)


def __virtual__():
    """
    Only load if strace is installed
    """
    if salt.utils.path.which("strace"):
        return __virtualname__
    else:
        err_msg = "strace is missing."
        log.error("Unable to load %s beacon: %s", __virtualname__, err_msg)
        return False, err_msg


def _get_shells():
    """
    Return the valid shells on this system
    """
    start = time.time()
    if "sh.last_shells" in __context__:
        if start - __context__["sh.last_shells"] > 5:
            __context__["sh.last_shells"] = start
        else:
            __context__["sh.shells"] = __salt__["cmd.shells"]()
    else:
        __context__["sh.last_shells"] = start
        __context__["sh.shells"] = __salt__["cmd.shells"]()
    return __context__["sh.shells"]


def validate(config):
    """
    Validate the beacon configuration
    """
    # Configuration for sh beacon should be a list of dicts
    if not isinstance(config, list):
        return False, "Configuration for sh beacon must be a list."
    return True, "Valid beacon configuration"


def beacon(config):
    """
    Scan the shell execve routines. This beacon will convert all login shells

    .. code-block:: yaml

        beacons:
          sh: []
    """
    ret = []
    pkey = "sh.vt"
    shells = _get_shells()
    ps_out = __salt__["status.procs"]()
    track_pids = []
    for pid in ps_out:
        if any(ps_out[pid].get("cmd", "").lstrip("-") in shell for shell in shells):
            track_pids.append(pid)
    if pkey not in __context__:
        __context__[pkey] = {}
    for pid in track_pids:
        if pid not in __context__[pkey]:
            cmd = ["strace", "-f", "-e", "execve", "-p", f"{pid}"]
            __context__[pkey][pid] = {}
            __context__[pkey][pid]["vt"] = salt.utils.vt.Terminal(
                cmd,
                log_stdout=True,
                log_stderr=True,
                stream_stdout=False,
                stream_stderr=False,
            )
            __context__[pkey][pid]["user"] = ps_out[pid].get("user")
    for pid in list(__context__[pkey]):
        out = ""
        err = ""
        while __context__[pkey][pid]["vt"].has_unread_data:
            tout, terr = __context__[pkey][pid]["vt"].recv()
            if not terr:
                break
            out += salt.utils.stringutils.to_unicode(tout or "")
            err += terr
        for line in err.split("\n"):
            event = {"args": [], "tag": pid}
            if "execve" in line:
                comps = line.split("execve")[1].split('"')
                for ind, field in enumerate(comps):
                    if ind == 1:
                        event["cmd"] = field
                        continue
                    if ind % 2 != 0:
                        event["args"].append(field)
                event["user"] = __context__[pkey][pid]["user"]
                ret.append(event)
        if not __context__[pkey][pid]["vt"].isalive():
            __context__[pkey][pid]["vt"].close()
            __context__[pkey].pop(pid)
    return ret