Try harder to attach to an existing tmux session

If in the course of an ssh/tmux session the tmux package is upgraded
and the ssh connection broken, the next ssh attempt will encounter an
error because of the tmux protocol version mismatch.

The old tmux can be used to reattach by searching for the tmux process
under /proc and using its reference to the old tmux executable. This
change attempts to do that automatically if a first "tmux attach"
attempt fails, but we can see that a previous session still exists.

install_files/ansible-base/roles/common/files/bashrc_securedrop_additions

@@ -1,9 +1,17 @@
-# If not running interactively, do not do anything
 [[ $- != *i* ]] && return
 
-# Auto-launch tmux on login
-# https://wiki.archlinux.org/index.php/Tmux#Start_tmux_on_every_shell_login
-if which tmux >/dev/null 2>&1; then
-    #if not inside a tmux session, and if no session is started, start a new session
-    test -z "$TMUX" && (tmux attach || tmux new-session)
-fi
+which tmux >/dev/null 2>&1 || return
+
+function tmux_attach_via_proc() {
+    pid=$(pgrep --newest tmux)
+    if test -n "$pid"
+    then
+        /proc/$pid/exe attach
+    fi
+    return 1
+}
+
+if test -z "$TMUX"
+then
+    (tmux attach || tmux_attach_via_proc || tmux new-session)
+fi

molecule/testinfra/staging/common/test_user_config.py

@@ -1,3 +1,5 @@
+import hashlib
+import os
 import re
 
 
@@ -38,16 +40,19 @@ def test_sudoers_tmux_env(host):
     the corresponding settings there.
     """
 
-    f = host.file('/etc/profile.d/securedrop_additions.sh')
-    non_interactive_str = re.escape('[[ $- != *i* ]] && return')
-    tmux_check = re.escape('test -z "$TMUX" && (tmux attach ||'
-                           ' tmux new-session)')
+    host_file = host.file('/etc/profile.d/securedrop_additions.sh')
+    source_file = os.path.abspath(
+        os.path.join(
+            os.path.dirname(__file__),
+            '../../../../install_files/ansible-base/roles/common/files/',
+            'bashrc_securedrop_additions'
+        )
+    )
+    expected_content = open(source_file).read()
+    h = hashlib.sha256()
+    h.update(expected_content)
 
-    assert f.contains("^{}$".format(non_interactive_str))
-    assert f.contains("^if which tmux >\/dev\/null 2>&1; then$")
-
-    assert 'test -z "$TMUX" && (tmux attach || tmux new-session)' in f.content
-    assert f.contains(tmux_check)
+    assert host_file.sha256sum == h.hexdigest()
 
 
 def test_tmux_installed(host):