Adds option to restore from backup file already on server.

when the '--no-transfer' argument is used with `./securedrop-admin restore`,
instead of transferring the backup tarball to the Application Server, the
local copy of the tarball will be compared with an expected remote file of the
same name in `/tmp` on the server. If checksums match, the remote copy will be
used to perform the backup.

This is intended to address cases where backups are too large to reliably
transmit over Tor via the Ansible synchronize module. Instead, backups can be
copied to the server using rsync, or via an encrypted transfer USB.

admin/securedrop_admin/__init__.py

@@ -883,25 +883,23 @@ def restore_securedrop(args: argparse.Namespace) -> int:
     # Would like readable output if there's a problem
     os.environ["ANSIBLE_STDOUT_CALLBACK"] = "debug"
 
-    ansible_cmd_full_restore = [
+    ansible_cmd = [
         'ansible-playbook',
         os.path.join(args.ansible_path, 'securedrop-restore.yml'),
         '-e',
-        "restore_file='{}'".format(restore_file_basename),
     ]
 
-    ansible_cmd_skip_tor = [
-        'ansible-playbook',
-        os.path.join(args.ansible_path, 'securedrop-restore.yml'),
-        '-e',
-        "restore_file='{}' restore_skip_tor='True'".format(restore_file_basename),
+    ansible_cmd_extras = [
+        "restore_file='{}'".format(restore_file_basename),
     ]
 
     if args.restore_skip_tor:
-        ansible_cmd = ansible_cmd_skip_tor
-    else:
-        ansible_cmd = ansible_cmd_full_restore
+        ansible_cmd_extras.append("restore_skip_tor='True'")
+
+    if args.restore_manual_transfer:
+        ansible_cmd_extras.append("restore_manual_transfer='True")
 
+    ansible_cmd.append(' '.join(ansible_cmd_extras))
     return subprocess.check_call(ansible_cmd, cwd=args.ansible_path)
 
 
@@ -1161,6 +1159,11 @@ class ArgParseFormatterCombo(argparse.ArgumentDefaultsHelpFormatter,
                                dest='restore_skip_tor',
                                help="Preserve the server's current Tor config")
 
+    parse_restore.add_argument("--no-transfer", default=False,
+                               action='store_true',
+                               dest='restore_manual_transfer',
+                               help="Restore using a backup file already present on the server")
+
     parse_update = subparsers.add_parser('update', help=update.__doc__)
     parse_update.set_defaults(func=update)
 

install_files/ansible-base/roles/restore/defaults/main.yml

@@ -3,3 +3,4 @@
 # backup. add the `--preserve-tor-config` to preserve the server's existing config.
 
 restore_skip_tor: False
+restore_manual_transfer: False

install_files/ansible-base/roles/restore/tasks/perform_restore.yml

@@ -53,11 +53,40 @@
       - "More info: {{ compare_result.stdout }}"
   when: not restore_skip_tor
 
+- name: Calculate local backup file checksum
+  connection: local
+  become: no
+  stat:
+    path: "{{ restore_file }}"
+    checksum_algorithm: sha256
+  register: local_backup_file
+  when: restore_manual_transfer
+
+- name: Calculate remote backup file checksum
+  stat:
+    path: "/tmp/{{ restore_file }}"
+    checksum_algorithm: sha256
+  register: remote_backup_file
+  when: restore_manual_transfer
+
+- name: Verify that local and remote backup file checksums match
+  assert:
+    that:
+      - "remote_backup_file.stat.checksum == local_backup_file.stat.checksum"
+    fail_msg:
+      - "Checksum comparison for the local and remote copies of the backup file failed."
+      - "When using the --no-transfer flag. the same file must be present both locally"
+      - "in `install_files/ansible-base and on the Application Server in `/tmp`, to allow"
+      - "for config verification. Please copy the backup file into place on the"
+      - "Application Server before proceeding, or restore without the --no-transfer flag."
+    when: restore_manual_transfer
+
 - name: Copy backup to application server
   synchronize:
     src: "{{ restore_file }}"
     dest: /tmp/{{ restore_file }}
     partial: yes
+  when: not restore_manual_transfer
 
 - name: Extract backup
   unarchive: