Subject: Using home-ssh-agent-configuration on Ubuntu breaks login
From: Janneke Nieuwenhuizen <[email-masked]>
To: [email-masked]
Date: Wed, 19 Apr 2023 18:28:16 +0200
List-Id: <debbugs-submit.debbugs.gnu.org>

Hi,

Using home-openssh-service-type on Ubuntu 22.10 (OpenSSH_9.3p1, OpenSSL
1.1.1t 7 Feb 2023) always creates an ~/.ssh/authorized_keys that breaks
key-based login.  I cannot access the logs and don't know what the
problem might be.

When, after running `guix home reconfigure', you do something like:

--8<---------------cut here---------------start------------->8---
mv .ssh/authorized_keys .ssh/authorized_keys-
cat .ssh/authorized_keys- > .ssh/authorized_keys
chmod 400 .ssh/authorized_keys
--8<---------------cut here---------------end--------------->8---
    
key-based login succeeds.

A workaround would be to have home-openssh-service-type leave
~/.ssh/authorized_keys alone.  However, when using

--8<---------------cut here---------------start------------->8---
(service
  home-openssh-service-type
  (home-openssh-configuration
   (authorized-keys '())))
--8<---------------cut here---------------end--------------->8---

any existing ~/.ssh/authorized_keys file is removed and replaced by a
symlink to an empty file.  I don't see how that is useful, it certainly
breaks key-based login.

Using

--8<---------------cut here---------------start------------->8---
(service
  home-openssh-service-type
  (home-openssh-configuration
   (authorized-keys #f)))
--8<---------------cut here---------------end--------------->8---

yields a backtrace.

The attached patch fixes that and allows using (authorized-keys #f),
also making this the default.

WDYT?

Greetings,
Janneke

From 1ca23618085ae0f5cbc4e989c591b2ee1cdede52 Mon Sep 17 00:00:00 2001
From: Janneke Nieuwenhuizen <[email-masked]>
Date: Wed, 19 Apr 2023 16:42:50 +0200
Subject: [PATCH] home: services: ssh: Support leaving ~/.ssh/authorized_keys
 alone.

The default was to remove any ~/.ssh/authorized_keys file and replace it with
a symlink to an empty file.  On some systems, notably Ubuntu 22.10, the guix
home generated ~/.ssh/authorized_keys file does not allow login.

* doc/guix.texi (Secure Shell): Update, describe default #false value.
* gnu/home/services/ssh.scm (<home-openssh-configuration>)
[authorized-keys]: Change default to #f.
(openssh-configuration-files): Cater for default #f value: Do not register
"authorized_keys".
---
 doc/guix.texi             |  8 +++++---
 gnu/home/services/ssh.scm | 22 ++++++++++++----------
 2 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/doc/guix.texi b/doc/guix.texi
index adb1975935..3736d24ff1 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -42565,9 +42565,11 @@ stateless: it can be replicated elsewhere or at another point in time.
 Preparing this list can be relatively tedious though, which is why
 @code{*unspecified*} is kept as a default.
 
-@item @code{authorized-keys} (default: @code{'()})
-This must be a list of file-like objects, each of which containing an
-SSH public key that should be authorized to connect to this machine.
+@item @code{authorized-keys} (default: @code{#false})
+The default @code{#false} value means: Leave any
+@file{~/.ssh/authorized_keys} file alone.  Otherwise, this must be a
+list of file-like objects, each of which containing an SSH public key
+that should be authorized to connect to this machine.
 
 Concretely, these files are concatenated and made available as
 @file{~/.ssh/authorized_keys}.  If an OpenSSH server, @command{sshd}, is
diff --git a/gnu/home/services/ssh.scm b/gnu/home/services/ssh.scm
index 01917a29cd..317808f616 100644
--- a/gnu/home/services/ssh.scm
+++ b/gnu/home/services/ssh.scm
@@ -186,7 +186,7 @@ (define-record-type* <home-openssh-configuration>
   home-openssh-configuration make-home-openssh-configuration
   home-openssh-configuration?
   (authorized-keys home-openssh-configuration-authorized-keys ;list of file-like
-                   (default '()))
+                   (default #f))
   (known-hosts     home-openssh-configuration-known-hosts ;unspec | list of file-like
                    (default *unspecified*))
   (hosts           home-openssh-configuration-hosts   ;list of <openssh-host>
@@ -222,19 +222,21 @@ (define* (file-join name files #:optional (delimiter " "))
                                      '#$files)))))))
 
 (define (openssh-configuration-files config)
-  (let ((config (plain-file "ssh.conf"
-                            (openssh-configuration->string config)))
-        (known-hosts (home-openssh-configuration-known-hosts config))
-        (authorized-keys (file-join
-                          "authorized_keys"
-                          (home-openssh-configuration-authorized-keys config)
-                          "\n")))
-    `((".ssh/authorized_keys" ,authorized-keys)
+  (let* ((ssh-config (plain-file "ssh.conf"
+                                 (openssh-configuration->string config)))
+         (known-hosts (home-openssh-configuration-known-hosts config))
+         (authorized-keys (home-openssh-configuration-authorized-keys config))
+         (authorized-keys (and
+                           authorized-keys
+                           (file-join "authorized_keys" authorized-keys "\n"))))
+    `(,@(if authorized-keys
+            `((".ssh/authorized_keys" ,authorized-keys))
+            '())
       ,@(if (unspecified? known-hosts)
             '()
             `((".ssh/known_hosts"
                ,(file-join "known_hosts" known-hosts "\n"))))
-      (".ssh/config" ,config))))
+      (".ssh/config" ,ssh-config))))
 
 (define openssh-activation
   (with-imported-modules (source-module-closure
-- 
2.39.2

-- 
Janneke Nieuwenhuizen <[email-masked]>  | GNU LilyPond https://LilyPond.org
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