Introduce --batch option to autorandr: Run autorandr for each user wi…

…th an X11 session

This is an attempt to resolve #45 and it might also be a better
alternative to #52, #44 and #39.

Makefile

@@ -50,10 +50,10 @@ ifeq ($(HAVE_SYSTEMD),y)
 DEFAULT_TARGETS+=systemd
 endif
 
-install_systemd: install_pmutils
+install_systemd:
 	install -D -m 644 contrib/systemd/autorandr-resume.service ${DESTDIR}/etc/systemd/system/autorandr-resume.service
 
-uninstall_systemd: uninstall_pmutils
+uninstall_systemd:
 	rm -f ${DESTDIR}/etc/systemd/system/autorandr-resume.service
 
 # Rules for udev
@@ -62,7 +62,7 @@ ifeq ($(HAVE_UDEV),y)
 DEFAULT_TARGETS+=udev
 endif
 
-install_udev: install_pmutils
+install_udev:
 	install -D -m 644 contrib/udev/40-monitor-hotplug.rules ${DESTDIR}/etc/udev/rules.d/40-monitor-hotplug.rules
 ifeq (${USER},root)
 	udevadm control --reload-rules
@@ -71,7 +71,7 @@ else
 	@echo "    udevadm control --reload-rules"
 endif
 
-uninstall_udev: uninstall_pmutils
+uninstall_udev:
 	rm -f ${DESTDIR}/etc/udev/rules.d/40-monitor-hotplug.rules
 
 

autorandr.py

@@ -30,6 +30,7 @@
 import hashlib
 import os
 import posix
+import pwd
 import re
 import subprocess
 import sys
@@ -69,6 +70,7 @@
 --config                dump your current xrandr setup
 --dry-run               don't change anything, only print the xrandr commands
 --debug                 enable verbose output
+--batch                 run autorandr for all users with active X11 sessions
 
  To prevent a profile from being loaded, place a script call "block" in its
  directory. The script is evaluated before the screen setup is inspected, and
@@ -756,15 +758,90 @@ def exec_scripts(profile_path, script_name, meta_information=None):
 
     return all_ok
 
+def dispatch_call_to_sessions(argv):
+    """Invoke autorandr for each open local X11 session with the given options.
+
+    The function iterates over all processes not owned by root and checks
+    whether they have a DISPLAY variable set. It strips the screen from any
+    variable it finds (i.e. :0.0 becomes :0) and checks whether this display
+    has been handled already. If it has not, it forks, changes uid/gid to
+    the user owning the process, reuses the process's environment and runs
+    autorandr with the parameters from argv.
+
+    This function requires root permissions. It only works for X11 servers that
+    have at least one non-root process running. It is susceptible for attacks
+    where one user runs a process with another user's DISPLAY variable - in
+    this case, it might happen that autorandr is invoked for the other user,
+    which won't work. Since no other harm than prevention of automated
+    execution of autorandr can be done this way, the assumption is that in this
+    situation, the local administrator will handle the situation."""
+    X11_displays_done = set()
+
+    autorandr_binary = os.path.abspath(argv[0])
+
+    for directory in os.listdir("/proc"):
+        directory = os.path.join("/proc/", directory)
+        if not os.path.isdir(directory):
+            continue
+        environ_file = os.path.join(directory, "environ")
+        if not os.path.isfile(environ_file):
+            continue
+        uid = os.stat(environ_file).st_uid
+        if uid == 0:
+            continue
+
+        process_environ = {}
+        for environ_entry in open(environ_file).read().split("\0"):
+            if "=" in environ_entry:
+                name, value = environ_entry.split("=", 1)
+                if name == "DISPLAY" and "." in value:
+                    value = value[:value.find(".")]
+                process_environ[name] = value
+        display = process_environ["DISPLAY"] if "DISPLAY" in process_environ else None
+
+        if display and display not in X11_displays_done:
+            try:
+                pwent = pwd.getpwuid(uid)
+            except KeyError:
+                # User has no pwd entry
+                continue
+
+            print("Running autorandr as %s for display %s" % (pwent.pw_name, display))
+            child_pid = os.fork()
+            if child_pid == 0:
+                # This will throw an exception if any of the privilege changes fails,
+                # so it should be safe. Also, note that since the environment
+                # is taken from a process owned by the user, reusing it should
+                # not leak any information.
+                os.setgroups([])
+                os.setresgid(pwent.pw_gid, pwent.pw_gid, pwent.pw_gid)
+                os.setresuid(pwent.pw_uid, pwent.pw_uid, pwent.pw_uid)
+                os.chdir(pwent.pw_dir)
+                os.environ.clear()
+                os.environ.update(process_environ)
+                os.execl(autorandr_binary, autorandr_binary, *argv[1:])
+                os.exit(1)
+            os.waitpid(child_pid, 0)
+
+            X11_displays_done.add(display)
+
 def main(argv):
     try:
-        options = dict(getopt.getopt(argv[1:], "s:r:l:d:cfh", [ "dry-run", "change", "default=", "save=", "remove=", "load=", "force", "fingerprint", "config", "debug", "skip-options=", "help" ])[0])
+        options = dict(getopt.getopt(argv[1:], "s:r:l:d:cfh", [ "batch", "dry-run", "change", "default=", "save=", "remove=", "load=", "force", "fingerprint", "config", "debug", "skip-options=", "help" ])[0])
     except getopt.GetoptError as e:
         print("Failed to parse options: {0}.\n"
               "Use --help to get usage information.".format(str(e)),
               file=sys.stderr)
         sys.exit(posix.EX_USAGE)
 
+    # Batch mode
+    if "--batch" in options:
+        if ("DISPLAY" not in os.environ or not os.environ["DISPLAY"]) and os.getuid() == 0:
+            dispatch_call_to_sessions([ x for x in argv if x != "--batch" ])
+        else:
+            print("--batch mode can only be used by root and if $DISPLAY is unset")
+        return
+
     profiles = {}
     try:
         # Load profiles from each XDG config directory

contrib/pm-utils/40autorandr

@@ -3,121 +3,8 @@
 # 40autorandr: Change autorandr profile on thaw/resume
 exec > /var/log/autorandr.log 2>&1
 
-AUTORANDR="autorandr -c --default default"
-
-# Work around #44: Long user names in w
-export PROCPS_USERLEN=32
-
-find_user() {
-	# Determine user owning the display session from $1
-	D="$1"
-
-	# Prefer loginctl over all others, see bug #39
-	if [ -x "`which loginctl`" ]; then
-		# Based on http://unix.stackexchange.com/questions/203844/how-to-find-out-the-current-active-xserver-display-number/204498
-		# by SO user intelfx
-		user="$(
-		loginctl list-sessions --no-legend | while read id uid user seat; do
-			session=$(loginctl show-session -p Display -p Active "$id")
-			first=$(echo $session | cut -d" " -f1)
-			second=$(echo $session | cut -d" " -f2)
-
-			if [ -n $(echo "$first" | grep "Display") ]; then
-				display=$first
-				active=$second
-			else
-				display=$second
-				active=$first
-			fi
-
-			active_value=$(echo "$active" | cut -d"=" -f2)
-			display_value=$(echo "$display" | cut -d"=" -f2)
-
-			if [ "$active_value" != "yes" ]; then
-				continue
-			fi
-
-			if [ -n $display_value -a "$display_value" = "$D" ]; then
-				echo $user
-			fi
-		done
-		)"
-		if [ -n "$user" ]; then
-			echo $user
-			return 0
-		fi
-	fi
-
-	# Prefer w to who, see bug #39
-	if [ -x "`which w`" ]; then
-		user="`w -h | awk -vD="$D" '$2 ~ ":"D"(.[0-9])?$" || $3 ~ ":"D"(.[0-9])?$" {print $1}' | head -n1`"
-
-		if [ -z "$user" ];	then
-			# This fallback checks if there is exactly one user (except
-			# root) logged in an interactive session and assumes the
-			# session belongs to him. See bug #39.
-			user="`w -hu | awk '/^\w+/ && $1 !~ "root" { users[$1]=$1; } ENDFILE { if(asort(users) == 1) for(u in users) print users[u]; }'`"
-		fi
-	else
-		user="`who --all | awk -vD="$D" '$3 ~ ":"D"(.[0-9])?$" {print $1}' | head -1`"
-
-		if [ -z "$user" ];	then
-			# Same fallback as above; see bug #39.
-			user="`who -u | awk '/^\w+/ && $1 !~ "root" { users[$1]=$1; } ENDFILE { if(asort(users) == 1) for(u in users) print users[u]; }'`"
-		fi
-	fi
-
-	if [ -n "$user" ]; then
-		echo $user
-		return 0
-	fi
-
-	# If none of the above worked, check if there is only one user owning
-	# processes in $DISPLAY except root
-	#
-	# This code should be optimized somehow, but keep in mind that not all
-	# systems symlink sh -> bash!
-	OUTPUT="$(
-		for p in /proc/*; do
-			[ -d $p ] || continue
-			d="$(awk -v RS='\0' -F= '$1=="DISPLAY" {print $2}' $p/environ 2>/dev/null)"
-			if [ "$d" = "$D" ]; then
-				stat -c %U $p
-			fi
-		done | sort | uniq | grep -v root | nl | head -n1
-	)"
-	count=$(echo $OUTPUT | awk '{print $1}')
-	user=$(echo $OUTPUT | awk '{print $2}')
-
-	if [ "$count" -eq 1 ]; then
-		echo $user
-		return 0
-	fi
-
-	return 1
-}
-
-detect_display()
-{
-	for X in /tmp/.X11-unix/X*; do
-		D="${X##/tmp/.X11-unix/X}"
-
-		user="$(find_user ":$D")"
-
-		if [ x"$user" != x"" ]; then
-			logger "autorandr: Changing display configuration for display :$D, user '$user'"
-			export DISPLAY=":$D"
-			/bin/su -c "${AUTORANDR}" "$user"
-		fi
-	done
-}
-
-if grep -q systemd /proc/1/comm && [ "$2" = "udev" ]; then
-    exec /bin/systemctl start autorandr-resume.service
-fi
-
 case "$1" in
 	thaw|resume)
-		detect_display
+		autorandr --batch -c --default default
 		;;
 esac

contrib/systemd/autorandr-resume.service

@@ -3,7 +3,7 @@ Description=autorandr resume hook
 After=sleep.target
 
 [Service]
-ExecStart=/etc/pm/sleep.d/40autorandr thaw
+ExecStart=/usr/bin/autorandr --batch -c --default default
 
 [Install]
-WantedBy=sleep.target
+WantedBy=sleep.target

contrib/udev/40-monitor-hotplug.rules

@@ -1 +1 @@
-ACTION=="change", SUBSYSTEM=="drm", RUN+="/etc/pm/sleep.d/40autorandr thaw udev"
+ACTION=="change", SUBSYSTEM=="drm", RUN+="/usr/bin/autorandr --batch -c --default default"