feat: add --egress-session-multiplexing option to accountModify

bin/helper/osh-accountModify

@@ -398,6 +398,50 @@ foreach my $tuple (@modify) {
             }
         }
     }
+    elsif ($key eq 'egress-session-multiplexing') {
+        osh_info "Changing the egress ControlMaster/ControlPath options for this account...";
+        my $controlPath;
+        my $controlMaster;
+        if ($value eq 'default') {
+            # keep both vars undef, which will remove them from the account config file
+            ;
+        }
+        elsif ($value eq 'yes') {
+            $controlMaster = 'auto';
+            # '~' is handled by ssh_config as the account's home directory
+            # '%C' is a hash of local hostname, remote host, remote user, remote port
+            $controlPath = "~/tmp/ssh_egress_%C";
+        }
+        elsif ($value eq 'no') {
+            # never create a master connection
+            $controlMaster = 'no';
+            # 'none' is understood specifically for ssh_config as 'never try to use a master connection'
+            $controlPath = 'none';
+        }
+        else {
+            osh_warn "Invalid parameter '$value', skipping";
+            $result{$jsonkey} = R('ERR_INVALID_PARAMETER');
+        }
+        $fnret = OVH::Bastion::account_ssh_config_set(
+            account => $account,
+            key     => "ControlMaster",
+            value   => $controlMaster,
+        );
+        if ($fnret) {
+            $fnret = OVH::Bastion::account_ssh_config_set(
+                account => $account,
+                key     => "ControlPath",
+                value   => $controlPath,
+            );
+        }
+        $result{$jsonkey} = $fnret;
+        if ($fnret) {
+            osh_info "... modification done";
+        }
+        else {
+            osh_warn "... error while setting policy: $fnret";
+        }
+    }
     elsif ($key eq 'personal-egress-mfa-required') {
         osh_info
           "Changing the MFA policy for egress connections using the personal access (and keys) of the account...";

bin/plugin/restricted/accountModify

@@ -19,6 +19,7 @@ my $remainingOptions = OVH::Bastion::Plugin::begin(
         "pam-auth-bypass=s"                 => \$modify{'pam-auth-bypass'},
         "always-active=s"                   => \$modify{'always-active'},
         "egress-strict-host-key-checking=s" => \$modify{'egress-strict-host-key-checking'},
+        "egress-session-multiplexing=s"     => \$modify{'egress-session-multiplexing'},
         "personal-egress-mfa-required=s"    => \$modify{'personal-egress-mfa-required'},
         "idle-ignore=s"                     => \$modify{'idle-ignore'},
         "max-inactive-days=i"               => \$modify{'max-inactive-days'},
@@ -47,6 +48,10 @@ Usage: --osh SCRIPT_NAME --account ACCOUNT [--option value [--option value [...]
                                                This effectively suppress the host key checking entirely. Please don't enable this blindly.
                                                'default' will remove this account's ``StrictHostKeyChecking`` setting override.
                                                All the other policies carry the same meaning that what is documented in `man ssh_config`.
+  --egress-session-multiplexing POLICY       Modify the egress SSH behavior of this account regarding ``ControlMaster`` and ``ControlPath``. POLICY can be:
+                                               'yes', setting ``ControlMaster`` to 'auto' and setting ``ControlPath`` properly for session sharing,
+                                               'no', setting ``ControlMaster`` to 'no' and ``ControlPath`` to 'none',
+                                               'default', removing this account ``ControlMaster`` and ``ControlPath`` overrides altogether.
   --personal-egress-mfa-required POLICY      Enforce UNIX password requirement, or TOTP requirement, or any MFA requirement, when connecting to a server
                                                using the personal keys of the account, POLICY can be 'password', 'totp', 'any' or 'none'
   --always-active yes|no                     Set or unset the account as always active (i.e. disable the check of the 'active' status on this account)
@@ -110,6 +115,12 @@ if ($modify{'personal-egress-mfa-required'} && !grep { $modify{'personal-egress-
     osh_exit 'ERR_INVALID_PARAMETER',
       "Expected option 'password', 'totp', 'any', 'none' to --personal-egress-mfa-required";
 }
+if ($modify{'egress-session-multiplexing'} && !grep { $modify{'egress-session-multiplexing'} eq $_ }
+    qw{ yes no default })
+{
+    help();
+    osh_exit 'ERR_INVALID_PARAMETER', "Expected option 'yes', 'no' or 'default' --egress-session-multiplexing";
+}
 if ($modify{'max-inactive-days'} && $modify{'max-inactive-days'} !~ /^(?:\d+|-1)$/) {
     help();
     osh_exit "ERR_INVALID_PARAMETER",

bin/shell/osh.pl

@@ -1570,6 +1570,10 @@ sub main_exit {
 # then convert to json:
 $ENV{'LC_BASTION_DETAILS'} = encode_json(\@details_json);
 
+# make sure $home/tmp exists, as it might be used for egress ssh connection multiplexing.
+# just attempt to create it instead of check+create, as it's not faster to do otherwise.
+mkdir "$home/tmp", 0700;
+
 # here is a nice hack to drastically improve the memory footprint of a
 # heavily used bastion. we exec() another script that is way lighter, see
 # comments in the connect.pl file for more information.

doc/sphinx/plugins/restricted/accountModify.rst

@@ -46,6 +46,13 @@ Modify an account configuration
                                                This effectively suppress the host key checking entirely. Please don't enable this blindly.
                                                'default' will remove this account's ``StrictHostKeyChecking`` setting override.
                                                All the other policies carry the same meaning that what is documented in `man ssh_config`.
+.. option:: --egress-session-multiplexing POLICY
+
+   Modify the egress SSH behavior of this account regarding ``ControlMaster`` and ``ControlPath``. POLICY can be:
+
+                                               'yes', setting ``ControlMaster`` to 'auto' and setting ``ControlPath`` properly for session sharing,
+                                               'no', setting ``ControlMaster`` to 'no' and ``ControlPath`` to 'none',
+                                               'default', removing this account ``ControlMaster`` and ``ControlPath`` overrides altogether.
 .. option:: --personal-egress-mfa-required POLICY
 
    Enforce UNIX password requirement, or TOTP requirement, or any MFA requirement, when connecting to a server

etc/bastion/osh-sync-watcher.rsyncfilter.dist

@@ -35,6 +35,7 @@
 - /home/*/*.log
 - /home/*/*.gz
 - /home/*/lastlog
+- /home/*/tmp/
 - /home/*/.ssh/known_hosts
 
 + /home/*/***