ssh-util: allow cloudinit to merge all ssh keys into a custom user file, defined in AuthorizedKeysFile (#937)

This patch aims to fix LP1911680, by analyzing the files provided
in sshd_config and merge all keys into an user-specific file. Also
introduces additional tests to cover this specific case.

The file is picked by analyzing the path given in AuthorizedKeysFile.

If it points inside the current user folder (path is /home/user/*), it
means it is an user-specific file, so we can copy all user-keys there.
If it contains a %u or %h, it means that there will be a specific
authorized_keys file for each user, so we can copy all user-keys there.
If no path points to an user-specific file, for example when only
/etc/ssh/authorized_keys is given, default to ~/.ssh/authorized_keys.
Note that if there are more than a single user-specific file, the last
one will be picked.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Co-authored-by: James Falcon <therealfalcon@gmail.com>

LP: #1911680
RHBZ:1862967

1 files changed, 19 insertions, 3 deletions

diff --git a/cloudinit/ssh_util.py b/cloudinit/ssh_util.py
index c08042d6..89057262 100644
--- a/cloudinit/ssh_util.py
+++ b/cloudinit/ssh_util.py
@@ -252,13 +252,15 @@ def render_authorizedkeysfile_paths(value, homedir, username):
 def extract_authorized_keys(username, sshd_cfg_file=DEF_SSHD_CFG):
     (ssh_dir, pw_ent) = users_ssh_info(username)
     default_authorizedkeys_file = os.path.join(ssh_dir, 'authorized_keys')
+    user_authorizedkeys_file = default_authorizedkeys_file
     auth_key_fns = []
     with util.SeLinuxGuard(ssh_dir, recursive=True):
         try:
             ssh_cfg = parse_ssh_config_map(sshd_cfg_file)
+            key_paths = ssh_cfg.get("authorizedkeysfile",
+                                    "%h/.ssh/authorized_keys")
             auth_key_fns = render_authorizedkeysfile_paths(
-                ssh_cfg.get("authorizedkeysfile", "%h/.ssh/authorized_keys"),
-                pw_ent.pw_dir, username)
+                key_paths, pw_ent.pw_dir, username)
 
         except (IOError, OSError):
             # Give up and use a default key filename
@@ -267,8 +269,22 @@ def extract_authorized_keys(username, sshd_cfg_file=DEF_SSHD_CFG):
                         "config from %r, using 'AuthorizedKeysFile' file "
                         "%r instead", DEF_SSHD_CFG, auth_key_fns[0])
 
+    # check if one of the keys is the user's one
+    for key_path, auth_key_fn in zip(key_paths.split(), auth_key_fns):
+        if any([
+            '%u' in key_path,
+            '%h' in key_path,
+            auth_key_fn.startswith('{}/'.format(pw_ent.pw_dir))
+        ]):
+            user_authorizedkeys_file = auth_key_fn
+
+    if user_authorizedkeys_file != default_authorizedkeys_file:
+        LOG.debug(
+            "AuthorizedKeysFile has an user-specific authorized_keys, "
+            "using %s", user_authorizedkeys_file)
+
     # always store all the keys in the user's private file
-    return (default_authorizedkeys_file, parse_authorized_keys(auth_key_fns))
+    return (user_authorizedkeys_file, parse_authorized_keys(auth_key_fns))
 
 
 def setup_user_keys(keys, username, options=None):