#!/bin/bash
#
# execsnoop - trace process exec() with arguments.
#             Written using Linux ftrace.
#
# This shows the execution of new processes, especially short-lived ones that
# can be missed by sampling tools such as top(1).
#
# USAGE: ./execsnoop [-hrt] [-n name]
#
# REQUIREMENTS: FTRACE and KPROBE CONFIG, sched:sched_process_fork tracepoint,
# and either the sys_execve, stub_execve or do_execve kernel function. You may
# already have these on recent kernels. And awk.
#
# This traces exec() from the fork()->exec() sequence, which means it won't
# catch new processes that only fork(). With the -r option, it will also catch
# processes that re-exec. It makes a best-effort attempt to retrieve the program
# arguments and PPID; if these are unavailable, 0 and "[?]" are printed
# respectively. There is also a limit to the number of arguments printed (by
# default, 8), which can be increased using -a.
#
# This implementation is designed to work on older kernel versions, and without
# kernel debuginfo. It works by dynamic tracing an execve kernel function to
# read the arguments from the %si register. The sys_execve function is tried
# first, then stub_execve and do_execve. The sched:sched_process_fork
# tracepoint is used to get the PPID. This program is a workaround that should be
# improved in the future when other kernel capabilities are made available. If
# you need a more reliable tool now, then consider other tracing alternatives
# (eg, SystemTap). This tool is really a proof of concept to see what ftrace can
# currently do.
#
# From perf-tools: https://github.com/brendangregg/perf-tools
#
# See the execsnoop(8) man page (in perf-tools) for more info.
#
# COPYRIGHT: Copyright (c) 2014 Brendan Gregg.
#
#  This program is free software; you can redistribute it and/or
#  modify it under the terms of the GNU General Public License
#  as published by the Free Software Foundation; either version 2
#  of the License, or (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program; if not, write to the Free Software Foundation,
#  Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
#
#  (http://www.gnu.org/copyleft/gpl.html)
#
# 07-Jul-2014	Brendan Gregg	Created this.

### default variables
tracing=/sys/kernel/debug/tracing
flock=/var/tmp/.ftrace-lock; wroteflock=0
opt_duration=0; duration=; opt_name=0; name=; opt_time=0; opt_reexec=0
opt_argc=0; argc=8; max_argc=16; ftext=
trap ':' INT QUIT TERM PIPE HUP	# sends execution to end tracing section

function usage {
	cat <<-END >&2
	USAGE: execsnoop [-hrt] [-a argc] [-d secs] [name]
	                 -d seconds      # trace duration, and use buffers
	                 -a argc         # max args to show (default 8)
	                 -r              # include re-execs
	                 -t              # include time (seconds)
	                 -h              # this usage message
	                 name            # process name to match (REs allowed)
	  eg,
	       execsnoop                 # watch exec()s live (unbuffered)
	       execsnoop -d 1            # trace 1 sec (buffered)
	       execsnoop grep            # trace process names containing grep
	       execsnoop 'log$'          # filenames ending in "log"

	See the man page and example file for more info.
END
	exit
}

function warn {
	if ! eval "$@"; then
		echo >&2 "WARNING: command failed \"$@\""
	fi
}

function end {
	# disable tracing
	echo 2>/dev/null
	echo "Ending tracing..." 2>/dev/null
	cd $tracing
	warn "echo 0 > events/kprobes/$kname/enable"
	warn "echo 0 > events/sched/sched_process_fork/enable"
	warn "echo -:$kname >> kprobe_events"
	warn "echo > trace"
	(( wroteflock )) && warn "rm $flock"
}

function die {
	echo >&2 "$@"
	exit 1
}

function edie {
	# die with a quiet end()
	echo >&2 "$@"
	exec >/dev/null 2>&1
	end
	exit 1
}

### process options
while getopts a:d:hrt opt
do
	case $opt in
	a)	opt_argc=1; argc=$OPTARG ;;
	d)	opt_duration=1; duration=$OPTARG ;;
	r)	opt_reexec=1 ;;
	t)	opt_time=1 ;;
	h|?)	usage ;;
	esac
done
shift $(( $OPTIND - 1 ))
if (( $# )); then
	opt_name=1
	name=$1
	shift
fi
(( $# )) && usage

### option logic
(( opt_pid && opt_name )) && die "ERROR: use either -p or -n."
(( opt_pid )) && ftext=" issued by PID $pid"
(( opt_name )) && ftext=" issued by process name \"$name\""
(( opt_file )) && ftext="$ftext for filenames containing \"$file\""
(( opt_argc && argc > max_argc )) && die "ERROR: max -a argc is $max_argc."
if (( opt_duration )); then
	echo "Tracing exec()s$ftext for $duration seconds (buffered)..."
else
	echo "Tracing exec()s$ftext. Ctrl-C to end."
fi

### select awk
if (( opt_duration )); then
	[[ -x /usr/bin/mawk ]] && awk=mawk || awk=awk
else
	# workarounds for mawk/gawk fflush behavior
	if [[ -x /usr/bin/gawk ]]; then
		awk=gawk
	elif [[ -x /usr/bin/mawk ]]; then
		awk="mawk -W interactive"
	else
		awk=awk
	fi
fi

### check permissions
cd $tracing || die "ERROR: accessing tracing. Root user? Kernel has FTRACE?
    debugfs mounted? (mount -t debugfs debugfs /sys/kernel/debug)"

### ftrace lock
[[ -e $flock ]] && die "ERROR: ftrace may be in use by PID $(cat $flock) $flock"
echo $$ > $flock || die "ERROR: unable to write $flock."
wroteflock=1

### build probe
if [[ -x /usr/bin/getconf ]]; then
	bits=$(getconf LONG_BIT)
else
	bits=64
	[[ $(uname -m) == i* ]] && bits=32
fi
(( offset = bits / 8 ))
function makeprobe {
	func=$1
	kname=execsnoop_$func
	kprobe="p:$kname $func"
	i=0
	while (( i < argc + 1 )); do
		# p:kname do_execve +0(+0(%si)):string +0(+8(%si)):string ...
		kprobe="$kprobe +0(+$(( i * offset ))(%si)):string"
		(( i++ ))
	done
}
# try in this order: sys_execve, stub_execve, do_execve
makeprobe sys_execve

### setup and begin tracing
echo nop > current_tracer
if ! echo $kprobe >> kprobe_events 2>/dev/null; then
	makeprobe stub_execve
	if ! echo $kprobe >> kprobe_events 2>/dev/null; then
	    makeprobe do_execve
	    if ! echo $kprobe >> kprobe_events 2>/dev/null; then
		    edie "ERROR: adding a kprobe for execve. Exiting."
        fi
	fi
fi
if ! echo 1 > events/kprobes/$kname/enable; then
	edie "ERROR: enabling kprobe for execve. Exiting."
fi
if ! echo 1 > events/sched/sched_process_fork/enable; then
	edie "ERROR: enabling sched:sched_process_fork tracepoint. Exiting."
fi
echo "Instrumenting $func"
(( opt_time )) && printf "%-16s " "TIMEs"
printf "%6s %6s %s\n" "PID" "PPID" "ARGS"

#
# Determine output format. It may be one of the following (newest first):
#           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
#           TASK-PID    CPU#    TIMESTAMP  FUNCTION
# To differentiate between them, the number of header fields is counted,
# and an offset set, to skip the extra column when needed.
#
offset=$($awk 'BEGIN { o = 0; }
	$1 == "#" && $2 ~ /TASK/ && NF == 6 { o = 1; }
	$2 ~ /TASK/ { print o; exit }' trace)

### print trace buffer
warn "echo > trace"
( if (( opt_duration )); then
	# wait then dump buffer
	sleep $duration
	cat -v trace
else
	# print buffer live
	cat -v trace_pipe
fi ) | $awk -v o=$offset -v opt_name=$opt_name -v name=$name \
    -v opt_duration=$opt_duration -v opt_time=$opt_time -v kname=$kname \
    -v opt_reexec=$opt_reexec '
	# common fields
	$1 != "#" {
		# task name can contain dashes
		comm = pid = $1
		sub(/-[0-9][0-9]*/, "", comm)
		sub(/.*-/, "", pid)
	}

	$1 != "#" && $(4+o) ~ /sched_process_fork/ {
		cpid=$0
		sub(/.* child_pid=/, "", cpid)
		sub(/ .*/, "", cpid)
		getppid[cpid] = pid
		delete seen[pid]
	}

	$1 != "#" && $(4+o) ~ kname {
		if (seen[pid])
			next
		if (opt_name && comm !~ name)
			next

		#
		# examples:
		# ... arg1="/bin/echo" arg2="1" arg3="2" arg4="3" ...
		# ... arg1="sleep" arg2="2" arg3=(fault) arg4="" ...
		# ... arg1="" arg2=(fault) arg3="" arg4="" ...
		# the last example is uncommon, and may be a race.
		#
		if ($0 ~ /arg1=""/) {
			args = comm " [?]"
		} else {
			args=$0
			sub(/ arg[0-9]*=\(fault\).*/, "", args)
			sub(/.*arg1="/, "", args)
			gsub(/" arg[0-9]*="/, " ", args)
			sub(/"$/, "", args)
			if ($0 !~ /\(fault\)/)
				args = args " [...]"
		}

		if (opt_time) {
			time = $(3+o); sub(":", "", time)
			printf "%-16s ", time
		}
		printf "%6s %6d %s\n", pid, getppid[pid], args
		if (!opt_duration)
			fflush()
		if (!opt_reexec) {
			seen[pid] = 1
			delete getppid[pid]
		}
	}

	$0 ~ /LOST.*EVENT[S]/ { print "WARNING: " $0 > "/dev/stderr" }
'

### end tracing
end
