commit 4ea5d02193d24b2fea90d785e965a7c9e596a3bc
parent cafef2e185ee147bc3d2fd32b2db358bb2ef91ae
Author: oblique <psyberbits@gmail.com>
Date: Sun, 26 Apr 2015 15:20:49 +0300
Implement recursive mutex that works across processes/threads
Diffstat:
| M | create_ap | | | 166 | ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--------- |
1 file changed, 148 insertions(+), 18 deletions(-)
diff --git a/create_ap b/create_ap
@@ -23,7 +23,8 @@ export LC_ALL=C
# all new files and directories must be readable only by root.
# in special cases we must use chmod to give any other permissions.
-umask 0077
+SCRIPT_UMASK=0077
+umask $SCRIPT_UMASK
usage() {
echo "Usage: "$PROGNAME" [options] <wifi-interface> [<interface-with-internet>] [<access-point-name> [<passphrase>]]"
@@ -82,6 +83,78 @@ usage() {
echo " "$PROGNAME" --stop wlan0"
}
+# allocate lock for the caller bash thread
+alloc_lock() {
+ # lock file for creating mutex
+ local LOCK_FILE=/tmp/create_ap.lock
+ local LOCK_FD=LOCK_FD_$BASHPID
+
+ # if lock FD is already allocated just return
+ eval "[[ \$$LOCK_FD -ne 0 ]]" && return 0
+
+ # use the lowest unused FD. avoid FD 0 because we use it to
+ # indicate that LOCK_FD_$BASHPID is not set.
+ for x in $(seq 1 $(ulimit -n)); do
+ if [[ ! -a "/proc/$BASHPID/fd/$x" ]]; then
+ eval "$LOCK_FD=$x"
+
+ # open/create lock file with write access for all users
+ # otherwise normal users will not be able to use it.
+ # to avoid race conditions on creation, we need to
+ # use umask to set the permissions.
+ umask 0555
+ eval "eval \"exec \$$LOCK_FD>$LOCK_FILE\"" > /dev/null 2>&1 || return 1
+ umask $SCRIPT_UMASK
+
+ # there is a case where lock file was created from a normal
+ # user. change the owner to root as soon as we can.
+ [[ $(id -u) -eq 0 ]] && chown 0:0 $LOCK_FILE
+
+ return 0
+ fi
+ done
+
+ return 1
+}
+
+# recursive mutex lock for all create_ap processes/threads.
+#
+# WARNING: if you lock in a function that their caller need their
+# output (i.e. the caller use | or $()) then you can have dead-lock
+# if the caller took the lock before. this happens because bash creates
+# a new thread for the callie function.
+mutex_lock() {
+ local MUTEX_COUNTER=MUTEX_COUNTER_$BASHPID
+ local LOCK_FD=LOCK_FD_$BASHPID
+
+ # allocate lock FD if needed
+ if eval "[[ \$$LOCK_FD -eq 0 ]]"; then
+ alloc_lock || die "Failed to allocate lock"
+ fi
+
+ # lock if needed and increase the counter
+ eval "[[ \$$MUTEX_COUNTER -eq 0 ]]" && eval "flock \$$LOCK_FD"
+ eval "$MUTEX_COUNTER=\$(( \$$MUTEX_COUNTER + 1 ))"
+
+ return 0
+}
+
+# recursive mutex unlock for all create_ap processes/threads
+mutex_unlock() {
+ local MUTEX_COUNTER=MUTEX_COUNTER_$BASHPID
+ local LOCK_FD=LOCK_FD_$BASHPID
+
+ # if lock FD was not allocated or we didn't lock before
+ # then just return
+ eval "[[ \$$LOCK_FD -eq 0 || \$$MUTEX_COUNTER -eq 0 ]]" && return 0
+
+ # unlock if needed and decrease the counter
+ eval "$MUTEX_COUNTER=\$(( \$$MUTEX_COUNTER - 1 ))"
+ eval "[[ \$$MUTEX_COUNTER -eq 0 ]]" && eval "flock -u \$$LOCK_FD"
+
+ return 0
+}
+
# it takes 2 arguments
# returns:
# 0 if v1 (1st argument) and v2 (2nd argument) are the same
@@ -246,24 +319,30 @@ get_macaddr() {
get_avail_bridge() {
local i=0
+ mutex_lock
while :; do
if ! is_interface br${i}; then
+ mutex_unlock
echo br${i}
return
fi
i=$((i + 1))
done
+ mutex_unlock
}
get_virt_iface_name() {
local i=0
+ mutex_lock
while :; do
if ! is_interface ap${i}; then
+ mutex_unlock
echo ap${i}
return
fi
i=$((i+1))
done
+ mutex_unlock
}
get_all_macaddrs() {
@@ -274,10 +353,12 @@ get_new_macaddr() {
local OLDMAC NEWMAC LAST_BYTE i
OLDMAC=$(get_macaddr "$1")
LAST_BYTE=$(printf %d 0x${OLDMAC##*:})
+ mutex_lock
for i in {1..255}; do
NEWMAC="${OLDMAC%:*}:$(printf %02x $(( ($LAST_BYTE + $i) % 256 )))"
(get_all_macaddrs | grep "$NEWMAC" > /dev/null 2>&1) || break
done
+ mutex_unlock
echo $NEWMAC
}
@@ -285,6 +366,7 @@ get_new_macaddr() {
haveged_watchdog() {
local show_warn=1
while :; do
+ mutex_lock
if [[ $(cat /proc/sys/kernel/random/entropy_avail) -lt 1000 ]]; then
if ! which haveged > /dev/null 2>&1; then
if [[ $show_warn -eq 1 ]]; then
@@ -297,9 +379,11 @@ haveged_watchdog() {
haveged -w 1024 -F > /dev/null 2>&1 &
local haveged_pid=$!
echo $haveged_pid > $CONFDIR/haveged.pid
+ mutex_unlock
wait $haveged_pid
fi
fi
+ mutex_unlock
sleep 2
done
}
@@ -354,14 +438,20 @@ networkmanager_add_unmanaged() {
[[ -z "$MAC" ]] && return 1
fi
+ mutex_lock
UNMANAGED=$(grep -m1 -Eo '^unmanaged-devices=[[:alnum:]:;,-]*' /etc/NetworkManager/NetworkManager.conf)
+
WAS_EMPTY=0
[[ -z "$UNMANAGED" ]] && WAS_EMPTY=1
UNMANAGED=$(echo "$UNMANAGED" | sed 's/unmanaged-devices=//' | tr ';,' ' ')
+ # if it exists, do nothing
for x in $UNMANAGED; do
- [[ $x == "mac:${MAC}" ]] && return 2
- [[ $NM_OLDER_VERSION -eq 0 && $x == "interface-name:${1}" ]] && return 2
+ if [[ $x == "mac:${MAC}" ]] ||
+ [[ $NM_OLDER_VERSION -eq 0 && $x == "interface-name:${1}" ]]; then
+ mutex_unlock
+ return 2
+ fi
done
if [[ $NM_OLDER_VERSION -eq 1 ]]; then
@@ -383,6 +473,7 @@ networkmanager_add_unmanaged() {
fi
ADDED_UNMANAGED="${ADDED_UNMANAGED} ${1} "
+ mutex_unlock
return 0
}
@@ -401,9 +492,13 @@ networkmanager_rm_unmanaged() {
[[ -z "$MAC" ]] && return 1
fi
+ mutex_lock
UNMANAGED=$(grep -m1 -Eo '^unmanaged-devices=[[:alnum:]:;,-]*' /etc/NetworkManager/NetworkManager.conf | sed 's/unmanaged-devices=//' | tr ';,' ' ')
- [[ -z "$UNMANAGED" ]] && return 1
+ if [[ -z "$UNMANAGED" ]]; then
+ mutex_unlock
+ return 1
+ fi
[[ -n "$MAC" ]] && UNMANAGED=$(echo $UNMANAGED | sed -e "s/mac:${MAC}\( \|$\)//g")
UNMANAGED=$(echo $UNMANAGED | sed -e "s/interface-name:${1}\( \|$\)//g")
@@ -418,13 +513,16 @@ networkmanager_rm_unmanaged() {
fi
ADDED_UNMANAGED="${ADDED_UNMANAGED/ ${1} /}"
+ mutex_unlock
return 0
}
networkmanager_fix_unmanaged() {
[[ -f ${NETWORKMANAGER_CONF} ]] || return
+ mutex_lock
sed -e "/^unmanaged-devices=.*/d" -i ${NETWORKMANAGER_CONF}
+ mutex_unlock
}
networkmanager_rm_unmanaged_if_needed() {
@@ -482,8 +580,9 @@ HAVEGED_WATCHDOG_PID=
_cleanup() {
local PID x
- trap "" SIGINT
- trap "" SIGUSR1
+ mutex_lock
+
+ trap "" SIGINT SIGUSR1 SIGUSR2
# kill haveged_watchdog
[[ -n "$HAVEGED_WATCHDOG_PID" ]] && kill $HAVEGED_WATCHDOG_PID
@@ -569,6 +668,8 @@ _cleanup() {
fi
networkmanager_rm_unmanaged_if_needed ${WIFI_IFACE} ${OLD_MACADDR}
fi
+
+ mutex_unlock
}
cleanup() {
@@ -580,15 +681,33 @@ cleanup() {
die() {
[[ -n "$1" ]] && echo -e "\nERROR: $1\n" >&2
- cleanup
- exit 1
+ # we cleanup and exit only if we are the main thread
+ if [[ $$ -eq $BASHPID ]]; then
+ cleanup
+ exit 1
+ else
+ # send die signal to the main thread
+ kill -USR2 $$
+ # terminate our thread
+ kill -9 $BASHPID
+ fi
}
clean_exit() {
- cleanup
- exit 0
+ # we cleanup and exit only if we are the main thread
+ if [[ $$ -eq $BASHPID ]]; then
+ cleanup
+ exit 0
+ else
+ # send clean_exit signal to the main thread
+ kill -USR1 $$
+ # terminate our thread
+ kill -9 $BASHPID
+ fi
}
+# WARNING: never call mutex_lock in this function, otherwise we
+# will have dead-lock when send_stop is called
list_running() {
local PID IFACE x
for x in /tmp/create_ap.*; do
@@ -610,9 +729,11 @@ is_running_pid() {
send_stop() {
local x
+ mutex_lock
# send stop signal to specific pid
if is_running_pid $1; then
kill -USR1 $1
+ mutex_unlock
return
fi
@@ -620,12 +741,9 @@ send_stop() {
for x in $(list_running | grep -E " ${1}\$" | cut -f1 -d' '); do
kill -USR1 $x
done
+ mutex_unlock
}
-# if the user press ctrl+c then execute die()
-trap "clean_exit" SIGINT
-trap "clean_exit" SIGUSR1
-
ARGS=( "$@" )
GETOPT_ARGS=$(getopt -o hc:w:g:dnm: -l "help","hidden","ieee80211n","ht_capab:","driver:","no-virt","fix-unmanaged","country:","freq-band:","mac:","daemon","stop:","list","version","no-haveged" -n "$PROGNAME" -- "$@")
[[ $? -ne 0 ]] && exit 1
@@ -740,8 +858,22 @@ if [[ $# -lt 1 && $FIX_UNMANAGED -eq 0 && -z "$STOP_ID" && $LIST_RUNNING -eq 0
exit 1
fi
+# allocate lock for the main thread to avoid any failures later
+if ! alloc_lock; then
+ echo "ERROR: Failed to allocate lock" >&2
+ exit 1
+fi
+
+# if the user press ctrl+c or we get USR1 signal
+# then run clean_exit()
+trap "clean_exit" SIGINT SIGUSR1
+# if we get USR2 signal then run die().
+trap "die" SIGUSR2
+
if [[ $LIST_RUNNING -eq 1 ]]; then
+ mutex_lock
list_running
+ mutex_unlock
exit 0
fi
@@ -951,6 +1083,7 @@ if [[ $NO_VIRT -eq 1 && "$WIFI_IFACE" == "$INTERNET_IFACE" ]]; then
exit 1
fi
+mutex_lock
CONFDIR=$(mktemp -d /tmp/create_ap.${WIFI_IFACE}.conf.XXXXXXXX)
echo "Config dir: $CONFDIR"
echo "PID: $$"
@@ -960,6 +1093,7 @@ echo $$ > $CONFDIR/pid
# permitions to $CONFDIR and $CONFDIR/pid
chmod 755 $CONFDIR
chmod 444 $CONFDIR/pid
+mutex_unlock
if [[ $NO_VIRT -eq 0 ]]; then
VWIFI_IFACE=$(get_virt_iface_name)
@@ -1198,10 +1332,6 @@ fi
# start access point
echo "hostapd command-line interface: hostapd_cli -p $CONFDIR/hostapd_ctrl"
-# from now on we exit with 0 on SIGINT
-trap "clean_exit" SIGINT
-trap "clean_exit" SIGUSR1
-
if [[ $NO_HAVEGED -eq 0 ]]; then
haveged_watchdog &
HAVEGED_WATCHDOG_PID=$!
