From a48fea4c5e53bace66f1730877e7b16178e5f7ea Mon Sep 17 00:00:00 2001
From: Niklas Hambüchen <mail@nh2.me>
Date: Sun, 11 Oct 2020 17:27:49 +0200
Subject: sshd service: Default to INFO logLevel (upstream default).

The previous justification for using "VERBOSE" is incorrect,
because OpenSSH does use level INFO to log "which key was used
to log in" for sccessful logins, see:
https://github.com/openssh/openssh-portable/blob/6247812c76f70b2245f3c23f5074665b3d436cae/auth.c#L323-L328

Also update description to the wording of the sshd_config man page.

`fail2ban` needs, sshd to be "VERBOSE" to work well, thus
the `fail2ban` module sets it to "VERBOSE" if enabled.

The docs are updated accordingly.
---
 nixos/modules/services/networking/ssh/sshd.nix |  7 ++-----
 nixos/modules/services/security/fail2ban.nix   | 19 ++++++++++++++++++-
 2 files changed, 20 insertions(+), 6 deletions(-)

(limited to 'nixos/modules')

diff --git a/nixos/modules/services/networking/ssh/sshd.nix b/nixos/modules/services/networking/ssh/sshd.nix
index 227dfe834b2..91caa2ccb42 100644
--- a/nixos/modules/services/networking/ssh/sshd.nix
+++ b/nixos/modules/services/networking/ssh/sshd.nix
@@ -351,15 +351,12 @@ in
 
       logLevel = mkOption {
         type = types.enum [ "QUIET" "FATAL" "ERROR" "INFO" "VERBOSE" "DEBUG" "DEBUG1" "DEBUG2" "DEBUG3" ];
-        default = "VERBOSE";
+        default = "INFO"; # upstream default
         description = ''
           Gives the verbosity level that is used when logging messages from sshd(8). The possible values are:
-          QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is VERBOSE. DEBUG and DEBUG1
+          QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO. DEBUG and DEBUG1
           are equivalent. DEBUG2 and DEBUG3 each specify higher levels of debugging output. Logging with a DEBUG level
           violates the privacy of users and is not recommended.
-
-          LogLevel VERBOSE logs user's key fingerprint on login.
-          Needed to have a clear audit track of which key was used to log in.
         '';
       };
 
diff --git a/nixos/modules/services/security/fail2ban.nix b/nixos/modules/services/security/fail2ban.nix
index 07702bfb9d0..499d3466750 100644
--- a/nixos/modules/services/security/fail2ban.nix
+++ b/nixos/modules/services/security/fail2ban.nix
@@ -45,7 +45,12 @@ in
       enable = mkOption {
         default = false;
         type = types.bool;
-        description = "Whether to enable the fail2ban service.";
+        description = ''
+          Whether to enable the fail2ban service.
+
+          See the documentation of <option>services.fail2ban.jails</option>
+          for what jails are enabled by default.
+        '';
       };
 
       package = mkOption {
@@ -221,6 +226,15 @@ in
           defined in <filename>/etc/fail2ban/action.d</filename>,
           while filters are defined in
           <filename>/etc/fail2ban/filter.d</filename>.
+
+          NixOS comes with a default <literal>sshd</literal> jail;
+          for it to work well,
+          <option>services.openssh.logLevel</option> should be set to
+          <literal>"VERBOSE"</literal> or higher so that fail2ban
+          can observe failed login attempts.
+          This module sets it to <literal>"VERBOSE"</literal> if
+          not set otherwise, so enabling fail2ban can make SSH logs
+          more verbose.
         '';
       };
 
@@ -313,6 +327,9 @@ in
       banaction_allports = ${cfg.banaction-allports}
     '';
     # Block SSH if there are too many failing connection attempts.
+    # Benefits from verbose sshd logging to observe failed login attempts,
+    # so we set that here unless the user overrode it.
+    services.openssh.logLevel = lib.mkDefault "VERBOSE";
     services.fail2ban.jails.sshd = mkDefault ''
       enabled = true
       port    = ${concatMapStringsSep "," (p: toString p) config.services.openssh.ports}
-- 
cgit 1.4.1