Why an applet can't be NOFORK or NOEXEC?

Why can't be NOFORK:
interactive: may wait for user input, ^C has to work
spawner: "tool PROG ARGS" which changes program state and execs - must fork
changes state: e.g. environment, signal handlers
leaks: does not free allocated memory or opened fds
	alloc+xfunc: xmalloc, then xfunc - leaks memory if xfunc dies
	open+xfunc: opens fd, then calls xfunc - fd is leaked if xfunc dies
talks to network/serial/etc: it's not known how long the delay can be,
	it's reasonable to expect it might be many seconds
	(even if usually it is not), so ^C has to work
runner: sometimes may run for long(ish) time, and/or works with network:
	^C has to work (cat BIGFILE, chmod -R, ftpget, nc)

"runners" can become eligible after shell is taught ^C to interrupt NOFORKs,
need to be inspected that they do not fall into alloc+xfunc, open+xfunc,
leak categories.

Why can't be NOEXEC:
suid: runs under different uid - must fork+exec
if it's important that /proc/PID/cmdline and comm are correct.
	("pkill sh" killing itself before it kills real "sh" is no fun)

Why shouldn't be NOFORK/NOEXEC:
rare: not started often enough to bother optimizing (example: poweroff)
daemon: runs indefinitely; these are also always fit "rare" category
longterm: often runs for a long time (many seconds), execing makes
	memory footprint smaller
complex: no immediately obvious reason why NOFORK wouldn't work,
	but does some non-obvoius operations (example: fuser, lsof, losetup);
	detailed audit often turns out that it's a leaker
hardware: performs unusual hardware ops which may take long,
	or even hang due to hardware or firmware bugs

Interesting example of "interactive" applet which is nevertheless can be
(and is) NOEXEC is "rm". Yes, "rm -i" is interactive - but it's not that typical
for users to keep it waiting for many minutes, whereas running "rm" in shell
is very typical, and speeding up this common use via NOEXEC is useful.
IOW: rm is "interactive", but not "longterm".

Interesting example of an applet which can be NOFORK but if not,
then should not be NOEXEC, is "usleep". As NOFORK, it amount to simply
nanosleep()ing in the calling program (usually shell). No memory wasted.
But if ran as NOEXEC, it would create a potentially long-term process,
which would be taking more memory because it did not exec
and did not free much of the copied memory of the parent
(COW helps with this only as long as parent doesn't modify its memory).


[ - NOFORK
[[ - NOFORK
acpid - daemon
add-shell - noexec. leaks: open+xfunc
addgroup - noexec. leaks
adduser - noexec. leaks
adjtimex - NOFORK
ar - runner
arch - NOFORK
arp - talks to network: arp -n queries DNS
arping - longterm
ash - interactive, longterm
awk - noexec. runner
base64 - runner
basename - NOFORK
beep - longterm: beep -r 999999999
blkdiscard - noexec. leaks: open+xioctl
blkid - noexec
blockdev - noexec. leaks fd
bootchartd - daemon
brctl - noexec
bunzip2 - runner
bzcat - runner
bzip2 - runner
cal - runner: cal -n9999
cat - runner: cat HUGEFILE
chat - longterm (when used as intended - talking to modem over stdin/out)
chattr - noexec. runner
chgrp - noexec. runner
chmod - noexec. runner
chown - noexec. runner
chpasswd - longterm? (list of "user:password"s from stdin)
chpst - noexec. spawner
chroot - noexec. spawner
chrt - noexec. spawner
chvt - noexec. leaks: get_console_fd_or_die() may open a new fd, or return one of stdio fds
cksum - noexec. runner
clear - NOFORK
cmp - runner
comm - runner
conspy - interactive, longterm
cp - noexec. runner
cpio - runner
crond - daemon
crontab - longterm (runs $EDITOR), leaks: open+xasprintf
cryptpw - noexec. changes state: with --password-fd=N, moves N to stdin
cttyhack - noexec. spawner
cut - noexec. runner
date - noexec. nofork candidate(needs to stop messing up env, free xasprintf result, not use xfuncs after xasprintf)
dc - longterm (eats stdin if no params)
dd - noexec. runner
deallocvt - noexec. leaks: get_console_fd_or_die() may open a new fd, or return one of stdio fds
delgroup - noexec. leaks
deluser - noexec. leaks
depmod - longterm(ish)
devmem - hardware (access to device memory may hang)
df - noexec. leaks: nested allocs
dhcprelay - daemon
diff - runner
dirname - NOFORK
dmesg - runner
dnsd - daemon
dnsdomainname - noexec. talks to network (may query DNS)
dos2unix - noexec. runner
dpkg - runner
du - runner
dumpkmap - noexec. leaks: get_console_fd_or_die() may open a new fd, or return one of stdio fds
dumpleases - noexec. leaks: open+xread
echo - NOFORK
ed - interactive, longterm
egrep - longterm runner ("CMD | egrep ..."  may run indefinitely, better to exec to conserve memory)
eject - hardware, leaks: open+ioctl_or_perror_and_die, changes state (moves fds)
env - noexec. spawner, changes state (env)
envdir - noexec. spawner
envuidgid - noexec. spawner
expand - runner
expr - noexec. leaks: nested allocs
factor - longterm (eats stdin if no params)
fakeidentd - daemon
false - NOFORK
fatattr - noexec. leaks: open+xioctl, complex
fbset - hardware, leaks: open+xfunc
fbsplash - runner, longterm
fdflush - hardware, leaks: open+ioctl_or_perror_and_die
fdformat - hardware, longterm
fdisk - interactive, longterm
fgconsole - noexec. leaks: get_console_fd_or_die() may open a new fd, or return one of stdio fds
fgrep - longterm runner ("CMD | fgrep ..."  may run indefinitely, better to exec to conserve memory)
find - noexec. runner
findfs - suid
flash_eraseall - hardware
flash_lock - hardware
flash_unlock - hardware
flashcp - hardware
flock - spawner, changes state (file locks), let's play safe and not be noexec
fold - noexec. runner
free - noexec. nofork candidate(struct globals, needs to close /proc/meminfo fd)
freeramdisk - noexec. leaks: open+ioctl_or_perror_and_die
fsck - interactive, longterm
fsck.minix - needs ^C
fsfreeze - noexec. leaks: open+xioctl
fstrim - noexec. leaks: open+xioctl, find_block_device -> readdir+xstrdup
fsync - NOFORK
ftpd - daemon
ftpget - runner
ftpput - runner
fuser - complex
getopt - noexec. leaks: many allocs
getty - interactive, longterm
grep - longterm runner ("CMD | grep ..."  may run indefinitely, better to exec to conserve memory)
groups - noexec
gunzip - runner
gzip - runner
halt - rare
hd - noexec. runner
hdparm - hardware
head - noexec. runner
hexdump - noexec. runner
hostid - NOFORK
hostname - noexec. talks to network (hostname -d may query DNS)
httpd - daemon
hush - interactive, longterm
hwclock - hardware (xioctl(RTC_RD_TIME))
i2cdetect - hardware
i2cdump - hardware
i2cget - hardware
i2cset - hardware
id - noexec
ifconfig - hardware? (mem_start NN io_addr NN irq NN), leaks: xsocket+ioctl_or_perror_and_die
ifenslave - noexec. leaks: xsocket+bb_perror_msg_and_die
ifplugd - daemon
inetd - daemon
init - daemon
inotifyd - daemon
insmod - noexec
install - runner
ionice - noexec. spawner
iostat - longterm: "iostat 1" runs indefinitely
ip - noexec candidate
ipaddr - noexec candidate
ipcalc - noexec. ipcalc -h talks to network
ipcrm - noexec
ipcs - noexec
iplink - noexec candidate
ipneigh - noexec candidate
iproute - noexec candidate
iprule - noexec candidate
iptunnel - noexec candidate
kbd_mode - noexec. leaks: xopen_nonblocking+xioctl
kill - NOFORK
killall - NOFORK
killall5 - NOFORK
klogd - daemon
last - runner (I've got 1300 lines of output when tried it)
less - interactive, longterm
link - NOFORK
linux32 - noexec. spawner
linux64 - noexec. spawner
linuxrc - daemon
ln - noexec
loadfont - noexec. leaks: config_open+bb_error_msg_and_die("map format")
loadkmap - noexec. leaks: get_console_fd_or_die() may open a new fd, or return one of stdio fds
logger - runner
login - suid, interactive, longterm
logname - NOFORK
losetup - noexec. complex
lpd - daemon
lpq - runner
lpr - runner
ls - noexec. runner
lsattr - noexec. runner
lsmod - noexec
lsof - complex
lspci - noexec. too rare to bother for nofork
lsscsi - noexec. too rare to bother for nofork
lsusb - noexec. too rare to bother for nofork
lzcat - runner
lzma - runner
lzop - runner
lzopcat - runner
makedevs - noexec
makemime - runner
man - spawner, interactive, longterm
md5sum - noexec. runner
mdev - daemon
mesg - NOFORK
microcom - interactive, longterm
mkdir - NOFORK
mkdosfs - needs ^C
mke2fs - needs ^C
mkfifo - noexec
mkfs.ext2 - needs ^C
mkfs.minix - needs ^C
mkfs.vfat - needs ^C
mknod - noexec
mkpasswd - noexec. changes state: with --password-fd=N, moves N to stdin
mkswap - needs ^C
mktemp - noexec. leaks: xstrdup+concat_path_file
modinfo - noexec
modprobe - noexec
more - interactive, longterm
mount - suid
mountpoint - noexec. leaks: option -n "print dev name": find_block_device -> readdir+xstrdup
mpstat - longterm: "mpstat 1" runs indefinitely
mt - hardware
mv - noexec candidate, runner
nameif - noexec. openlog(), leaks: config_open2+ioctl_or_perror_and_die
nbd-client - noexec
nc - runner
netstat - longterm with -c (continuous listing)
nice - noexec. spawner
nl - runner
nmeter - longterm
nohup - noexec. spawner
nproc - NOFORK
ntpd - daemon
od - runner
openvt - longterm: spawns a child and waits for it
partprobe - noexec. leaks: open+ioctl_or_perror_and_die(BLKRRPART)
passwd - suid
paste - noexec. runner
patch - needs ^C
pgrep - must fork+exec to get correct /proc/PID/cmdline and comm field
pidof - must fork+exec to get correct /proc/PID/cmdline and comm field
ping - suid, longterm
ping6 - suid, longterm
pipe_progress - longterm
pivot_root - NOFORK
pkill - must fork+exec to get correct /proc/PID/cmdline and comm field
pmap - noexec candidate, leaks: open+xstrdup
popmaildir - runner
poweroff - rare
powertop - interactive, longterm
printenv - NOFORK
printf - NOFORK
ps - noexec
pscan - talks to network
pstree - noexec
pwd - NOFORK
pwdx - NOFORK
raidautorun - noexec. very simple. leaks: open+xioctl
rdate - talks to network
rdev - noexec. leaks: find_block_device -> readdir+xstrdup
readlink - NOFORK
readprofile - reads /boot/System.map and /proc/profile, better to free more memory by execing?
realpath - NOFORK
reboot - rare
reformime - runner
remove-shell - noexec. leaks: open+xfunc
renice - noexec. nofork candidate(uses getpwnam, is that ok?)
reset - noexec. spawner (execs "stty")
resize - noexec. changes state (signal handlers)
rev - runner
rm - noexec. rm -i interactive
rmdir - NOFORK
rmmod - noexec
route - talks to network (may query DNS to convert IPs to names)
rpm - runner
rpm2cpio - runner
rtcwake - longterm: puts system to sleep, optimizing this for speed is pointless
run-parts - longterm
runlevel - noexec. can be nofork if "endutxent()" is called unconditionally, but too rare to bother?
runsv - daemon
runsvdir - daemon
rx - runner
script - longterm: pumps script output from slave pty
scriptreplay - longterm: plays back "script" saved output, sleeping as necessary.
sed - runner
sendmail - runner
seq - noexec. runner
setarch - noexec. spawner
setconsole - noexec
setfont - noexec. leaks a lot of stuff
setkeycodes - noexec
setlogcons - noexec
setpriv - spawner, changes state, let's play safe and not be noexec
setserial - noexec
setsid - spawner, uses fork_or_rexec() [not audited to work in noexec], let's play safe and not be noexec
setuidgid - noexec. spawner
sha1sum - noexec. runner
sha256sum - noexec. runner
sha3sum - noexec. runner
sha512sum - noexec. runner
showkey - interactive, longterm
shred - runner
shuf - noexec. runner
slattach - longterm (may sleep forever), uses bb_common_bufsiz1
sleep - longterm. Could be nofork, if not the problem of "killall sleep" not killing it.
smemcap - runner
softlimit - noexec. spawner
sort - noexec. runner
split - runner
ssl_client - longterm
start-stop-daemon - not noexec: uses bb_common_bufsiz1
stat - noexec. nofork candidate(needs fewer allocs)
strings - runner
stty - noexec. nofork candidate: has no allocs or opens except xmove_fd(xopen("-F DEVICE"),STDIN). tcsetattr(STDIN) is not a problem: it would work the same across processes sharing this fd
su - suid, spawner
sulogin - noexec. spawner
sum - runner
sv - noexec. needs ^C (uses usleep(420000))
svc - noexec. needs ^C (uses usleep(420000))
svlogd - daemon
swapoff - longterm: may cause memory pressure, execing is beneficial
swapon - rare
switch_root - spawner, rare, changes state (oh yes), execing may be important to free binary's inode
sync - NOFORK
sysctl - noexec. leaks: xstrdup+xmalloc_read
syslogd - daemon
tac - noexec. runner
tail - runner
tar - runner
taskset - noexec. spawner
tcpsvd - daemon
tee - runner
telnet - interactive, longterm
telnetd - daemon
test - NOFORK
tftp - runner
tftpd - daemon
time - spawner, longterm, changes state (signals)
timeout - spawner, longterm, changes state (signals)
top - interactive, longterm
touch - NOFORK
tr - runner
traceroute - suid, longterm
traceroute6 - suid, longterm
true - NOFORK
truncate - NOFORK
tty - NOFORK
ttysize - NOFORK
tunctl - noexec
tune2fs - noexec. leaks: open+xfunc
ubiattach - hardware
ubidetach - hardware
ubimkvol - hardware
ubirename - hardware
ubirmvol - hardware
ubirsvol - hardware
ubiupdatevol - hardware
udhcpc - daemon
udhcpd - daemon
udpsvd - daemon
uevent - daemon
umount - noexec. leaks: nested xmalloc
uname - NOFORK
uncompress - runner
unexpand - runner
uniq - runner
unix2dos - noexec. runner
unlink - NOFORK
unlzma - runner
unlzop - runner
unxz - runner
unzip - runner
uptime - noexec. nofork candidate(is getutxent ok?)
users - noexec. nofork candidate(is getutxent ok?)
usleep - NOFORK. But what about "killall usleep"?
uudecode - runner
uuencode - runner
vconfig - noexec. leaks: xsocket+ioctl_or_perror_and_die
vi - interactive, longterm
vlock - suid
volname - hardware (reads CDROM, this can take long-ish if need to spin up)
w - noexec. nofork candidate(is getutxent ok?)
wall - suid
watch - longterm
watchdog - daemon
wc - runner
wget - longterm
which - NOFORK
who - noexec. nofork candidate(is getutxent ok?)
whoami - NOFORK
whois - talks to network
xargs - noexec. spawner
xxd - noexec. runner
xz - runner
xzcat - runner
yes - noexec. runner
zcat - runner
zcip - daemon