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

1 files changed, 30 insertions, 5 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