backport bug fix: start a new ssh-agent instance only if necessary (fixes bit-team#722)

Author: Germar

CHANGES

@@ -1,6 +1,7 @@
 Back In Time
 
 Version 1.1.15
+* backport bug fix: start a new ssh-agent instance only if necessary (https://github.com/bit-team/backintime/issues/722)
 * Fix bug: OSError when running backup-job from systemd (https://github.com/bit-team/backintime/issues/720)
 
 Version 1.1.14

common/backintime

@@ -24,8 +24,4 @@ else
 	APP_PATH=$(readlink -m "${CUR_PATH}/../share/backintime/common")
 fi
 
-#starting a new ssh-agent all the time is just a workaround for
-#https://bugs.launchpad.net/ubuntu/+source/openssh/+bug/841672
-#normally this should only be necessary if run as cronjob
-#and the user is not logged in
-ssh-agent python3 $APP_PATH/backintime.py "$@"
+python3 $APP_PATH/backintime.py "$@"

common/backintime.py

@@ -19,6 +19,7 @@
 import sys
 import gettext
 import argparse
+import subprocess
 
 import config
 import logger
@@ -57,7 +58,15 @@ def take_snapshot_now_async( cfg ):
         cmd += '--debug '
     cmd += 'backup &'
 
-    os.system( cmd )
+    # child process need to start it's own ssh-agent because otherwise
+    # it would be lost without ssh-agent if parent will close
+    env = os.environ.copy()
+    for i in ('SSH_AUTH_SOCK', 'SSH_AGENT_PID'):
+        try:
+            del env[i]
+        except:
+            pass
+    subprocess.Popen(cmd, env = env)
 
 def take_snapshot( cfg, force = True ):
     '''take a new snapshot.

common/sshtools.py

@@ -22,6 +22,9 @@
 import random
 import tempfile
 import socket
+import re
+import atexit
+import signal
 from time import sleep
 
 import config
@@ -167,8 +170,42 @@ def post_umount_check(self):
            raise MountException( _('Error discription') ) if not"""
         return True
 
+    def startSshAgent(self):
+        """
+        Start a new ``ssh-agent`` if it is not already running.
+
+        Raises:
+            exceptions.MountException:  if starting ``ssh-agent`` failed
+        """
+        SOCK = 'SSH_AUTH_SOCK'
+        PID  = 'SSH_AGENT_PID'
+        if os.getenv(SOCK, '') and os.getenv(PID, ''):
+            logger.debug('ssh-agent already running. Skip starting a new one.', self)
+            return
+        sa = subprocess.Popen([tools.which('ssh-agent')],
+                              stdout = subprocess.PIPE,
+                              stderr = subprocess.PIPE,
+                              universal_newlines = True)
+        out, err = sa.communicate()
+
+        if sa.returncode:
+            raise MountException('Failed to start ssh-agent: [{}] {}'.format(sa.returncode, err))
+
+        m = re.match(r'{}=([^;]+);.*{}=(\d+);'.format(SOCK, PID), out, re.DOTALL)
+        if m:
+            logger.debug('ssh-agent started successful: {}={} | {}={}'.format(SOCK, m.group(1), PID, m.group(2)), self)
+            os.environ[SOCK] = m.group(1)
+            os.environ[PID]  = m.group(2)
+            atexit.register(os.kill, int(m.group(2)), signal.SIGKILL)
+        else:
+            raise MountException('No matching output from ssh-agent: {} | {}'.format(out, err))
+
+
     def unlock_ssh_agent(self, force = False):
         """using askpass.py to unlock private key in ssh-agent"""
+
+        self.startSshAgent()
+
         env = os.environ.copy()
         env['SSH_ASKPASS'] = 'backintime-askpass'
         env['ASKPASS_PROFILE_ID'] = self.profile_id

qt4/backintime-qt4

@@ -28,8 +28,4 @@ else
 	APP_PATH=$(readlink -m "${CUR_PATH}/../share/backintime/qt4")
 fi
 
-#if [ "x$SSH_AUTH_SOCK" = "x" ]; then
-#        eval "$(ssh-agent)"
-#fi
-
-ssh-agent python3 ${APP_PATH}/app.py "$@"
+python3 ${APP_PATH}/app.py "$@"