Fix home permissions modified by ssh module (SC-338) (#984)

Fix home permissions modified by ssh module

In #956, we updated the file and directory permissions for keys not in
the user's home directory. We also unintentionally modified the
permissions within the home directory as well. These should not change,
and this commit changes that back.

LP: #1940233

2 files changed, 146 insertions, 21 deletions

diff --git a/cloudinit/ssh_util.py b/cloudinit/ssh_util.py
index b8a3c8f7..9ccadf09 100644
--- a/cloudinit/ssh_util.py
+++ b/cloudinit/ssh_util.py
@@ -321,23 +321,48 @@ def check_create_path(username, filename, strictmodes):
         home_folder = os.path.dirname(user_pwent.pw_dir)
         for directory in directories:
             parent_folder += "/" + directory
-            if home_folder.startswith(parent_folder):
+
+            # security check, disallow symlinks in the AuthorizedKeysFile path.
+            if os.path.islink(parent_folder):
+                LOG.debug(
+                    "Invalid directory. Symlink exists in path: %s",
+                    parent_folder)
+                return False
+
+            if os.path.isfile(parent_folder):
+                LOG.debug(
+                    "Invalid directory. File exists in path: %s",
+                    parent_folder)
+                return False
+
+            if (home_folder.startswith(parent_folder) or
+                    parent_folder == user_pwent.pw_dir):
                 continue
 
-            if not os.path.isdir(parent_folder):
+            if not os.path.exists(parent_folder):
                 # directory does not exist, and permission so far are good:
                 # create the directory, and make it accessible by everyone
                 # but owned by root, as it might be used by many users.
                 with util.SeLinuxGuard(parent_folder):
-                    os.makedirs(parent_folder, mode=0o755, exist_ok=True)
-                    util.chownbyid(parent_folder, root_pwent.pw_uid,
-                                   root_pwent.pw_gid)
+                    mode = 0o755
+                    uid = root_pwent.pw_uid
+                    gid = root_pwent.pw_gid
+                    if parent_folder.startswith(user_pwent.pw_dir):
+                        mode = 0o700
+                        uid = user_pwent.pw_uid
+                        gid = user_pwent.pw_gid
+                    os.makedirs(parent_folder, mode=mode, exist_ok=True)
+                    util.chownbyid(parent_folder, uid, gid)
 
             permissions = check_permissions(username, parent_folder,
                                             filename, False, strictmodes)
             if not permissions:
                 return False
 
+        if os.path.islink(filename) or os.path.isdir(filename):
+            LOG.debug("%s is not a file!", filename)
+            return False
+
         # check the file
         if not os.path.exists(filename):
             # if file does not exist: we need to create it, since the
diff --git a/tests/integration_tests/modules/test_ssh_keysfile.py b/tests/integration_tests/modules/test_ssh_keysfile.py
index f82d7649..3159feb9 100644
--- a/tests/integration_tests/modules/test_ssh_keysfile.py
+++ b/tests/integration_tests/modules/test_ssh_keysfile.py
@@ -10,10 +10,10 @@ TEST_USER1_KEYS = get_test_rsa_keypair('test1')
 TEST_USER2_KEYS = get_test_rsa_keypair('test2')
 TEST_DEFAULT_KEYS = get_test_rsa_keypair('test3')
 
-USERDATA = """\
+_USERDATA = """\
 #cloud-config
 bootcmd:
- - sed -i 's;#AuthorizedKeysFile.*;AuthorizedKeysFile /etc/ssh/authorized_keys %h/.ssh/authorized_keys2;' /etc/ssh/sshd_config
+ - {bootcmd}
 ssh_authorized_keys:
  - {default}
 users:
@@ -24,27 +24,17 @@ users:
 - name: test_user2
   ssh_authorized_keys:
     - {user2}
-""".format(  # noqa: E501
+""".format(
+    bootcmd='{bootcmd}',
     default=TEST_DEFAULT_KEYS.public_key,
     user1=TEST_USER1_KEYS.public_key,
     user2=TEST_USER2_KEYS.public_key,
 )
 
 
-@pytest.mark.ubuntu
-@pytest.mark.user_data(USERDATA)
-def test_authorized_keys(client: IntegrationInstance):
-    expected_keys = [
-        ('test_user1', '/home/test_user1/.ssh/authorized_keys2',
-         TEST_USER1_KEYS),
-        ('test_user2', '/home/test_user2/.ssh/authorized_keys2',
-         TEST_USER2_KEYS),
-        ('ubuntu', '/home/ubuntu/.ssh/authorized_keys2',
-         TEST_DEFAULT_KEYS),
-        ('root', '/root/.ssh/authorized_keys2', TEST_DEFAULT_KEYS),
-    ]
-
+def common_verify(client, expected_keys):
     for user, filename, keys in expected_keys:
+        # Ensure key is in the key file
         contents = client.read_from_file(filename)
         if user in ['ubuntu', 'root']:
             # Our personal public key gets added by pycloudlib
@@ -83,3 +73,113 @@ def test_authorized_keys(client: IntegrationInstance):
                     look_for_keys=False,
                     allow_agent=False,
                 )
+
+        # Ensure we haven't messed with any /home permissions
+        # See LP: #1940233
+        home_dir = '/home/{}'.format(user)
+        home_perms = '755'
+        if user == 'root':
+            home_dir = '/root'
+            home_perms = '700'
+        assert '{} {}'.format(user, home_perms) == client.execute(
+            'stat -c "%U %a" {}'.format(home_dir)
+        )
+        if client.execute("test -d {}/.ssh".format(home_dir)).ok:
+            assert '{} 700'.format(user) == client.execute(
+                'stat -c "%U %a" {}/.ssh'.format(home_dir)
+            )
+        assert '{} 600'.format(user) == client.execute(
+            'stat -c "%U %a" {}'.format(filename)
+        )
+
+        # Also ensure ssh-keygen works as expected
+        client.execute('mkdir {}/.ssh'.format(home_dir))
+        assert client.execute(
+            "ssh-keygen -b 2048 -t rsa -f {}/.ssh/id_rsa -q -N ''".format(
+                home_dir)
+        ).ok
+        assert client.execute('test -f {}/.ssh/id_rsa'.format(home_dir))
+        assert client.execute('test -f {}/.ssh/id_rsa.pub'.format(home_dir))
+
+    assert 'root 755' == client.execute('stat -c "%U %a" /home')
+
+
+DEFAULT_KEYS_USERDATA = _USERDATA.format(bootcmd='""')
+
+
+@pytest.mark.ubuntu
+@pytest.mark.user_data(DEFAULT_KEYS_USERDATA)
+def test_authorized_keys_default(client: IntegrationInstance):
+    expected_keys = [
+        ('test_user1', '/home/test_user1/.ssh/authorized_keys',
+         TEST_USER1_KEYS),
+        ('test_user2', '/home/test_user2/.ssh/authorized_keys',
+         TEST_USER2_KEYS),
+        ('ubuntu', '/home/ubuntu/.ssh/authorized_keys',
+         TEST_DEFAULT_KEYS),
+        ('root', '/root/.ssh/authorized_keys', TEST_DEFAULT_KEYS),
+    ]
+    common_verify(client, expected_keys)
+
+
+AUTHORIZED_KEYS2_USERDATA = _USERDATA.format(bootcmd=(
+    "sed -i 's;#AuthorizedKeysFile.*;AuthorizedKeysFile "
+    "/etc/ssh/authorized_keys %h/.ssh/authorized_keys2;' "
+    "/etc/ssh/sshd_config"))
+
+
+@pytest.mark.ubuntu
+@pytest.mark.user_data(AUTHORIZED_KEYS2_USERDATA)
+def test_authorized_keys2(client: IntegrationInstance):
+    expected_keys = [
+        ('test_user1', '/home/test_user1/.ssh/authorized_keys2',
+         TEST_USER1_KEYS),
+        ('test_user2', '/home/test_user2/.ssh/authorized_keys2',
+         TEST_USER2_KEYS),
+        ('ubuntu', '/home/ubuntu/.ssh/authorized_keys2',
+         TEST_DEFAULT_KEYS),
+        ('root', '/root/.ssh/authorized_keys2', TEST_DEFAULT_KEYS),
+    ]
+    common_verify(client, expected_keys)
+
+
+NESTED_KEYS_USERDATA = _USERDATA.format(bootcmd=(
+    "sed -i 's;#AuthorizedKeysFile.*;AuthorizedKeysFile "
+    "/etc/ssh/authorized_keys %h/foo/bar/ssh/keys;' "
+    "/etc/ssh/sshd_config"))
+
+
+@pytest.mark.ubuntu
+@pytest.mark.user_data(NESTED_KEYS_USERDATA)
+def test_nested_keys(client: IntegrationInstance):
+    expected_keys = [
+        ('test_user1', '/home/test_user1/foo/bar/ssh/keys',
+         TEST_USER1_KEYS),
+        ('test_user2', '/home/test_user2/foo/bar/ssh/keys',
+         TEST_USER2_KEYS),
+        ('ubuntu', '/home/ubuntu/foo/bar/ssh/keys',
+         TEST_DEFAULT_KEYS),
+        ('root', '/root/foo/bar/ssh/keys', TEST_DEFAULT_KEYS),
+    ]
+    common_verify(client, expected_keys)
+
+
+EXTERNAL_KEYS_USERDATA = _USERDATA.format(bootcmd=(
+    "sed -i 's;#AuthorizedKeysFile.*;AuthorizedKeysFile "
+    "/etc/ssh/authorized_keys /etc/ssh/authorized_keys/%u/keys;' "
+    "/etc/ssh/sshd_config"))
+
+
+@pytest.mark.ubuntu
+@pytest.mark.user_data(EXTERNAL_KEYS_USERDATA)
+def test_external_keys(client: IntegrationInstance):
+    expected_keys = [
+        ('test_user1', '/etc/ssh/authorized_keys/test_user1/keys',
+         TEST_USER1_KEYS),
+        ('test_user2', '/etc/ssh/authorized_keys/test_user2/keys',
+         TEST_USER2_KEYS),
+        ('ubuntu', '/etc/ssh/authorized_keys/ubuntu/keys',
+         TEST_DEFAULT_KEYS),
+        ('root', '/etc/ssh/authorized_keys/root/keys', TEST_DEFAULT_KEYS),
+    ]
+    common_verify(client, expected_keys)