openssh: Enable DSA host/client keys

This applies a patch from Fedora to make HostKeyAlgorithms do the
right thing, fixing the issue described in
401782cb67.

nixos/modules/programs/ssh.nix

@@ -186,6 +186,9 @@ in
 
         ForwardX11 ${if cfg.forwardX11 then "yes" else "no"}
 
+        # Allow DSA keys for now. (These were deprecated in OpenSSH 7.0.)
+        PubkeyAcceptedKeyTypes +ssh-dss
+
         ${cfg.extraConfig}
       '';
 

nixos/modules/services/networking/ssh/sshd.nix

@@ -52,6 +52,8 @@ let
     ));
   in listToAttrs (map mkAuthKeyFile usersWithKeys);
 
+  supportOldHostKeys = !versionAtLeast config.system.stateVersion "15.07";
+
 in
 
 {
@@ -177,7 +179,7 @@ in
         default =
           [ { type = "rsa"; bits = 4096; path = "/etc/ssh/ssh_host_rsa_key"; }
             { type = "ed25519"; path = "/etc/ssh/ssh_host_ed25519_key"; }
-          ] ++ optionals (!versionAtLeast config.system.stateVersion "15.07")
+          ] ++ optionals supportOldHostKeys
           [ { type = "dsa"; path = "/etc/ssh/ssh_host_dsa_key"; }
             { type = "ecdsa"; bits = 521; path = "/etc/ssh/ssh_host_ecdsa_key"; }
           ];
@@ -347,6 +349,15 @@ in
         ${flip concatMapStrings cfg.hostKeys (k: ''
           HostKey ${k.path}
         '')}
+
+        # Allow DSA client keys for now. (These were deprecated
+        # in OpenSSH 7.0.)
+        PubkeyAcceptedKeyTypes +ssh-dss
+
+        # Re-enable DSA host keys for now.
+        ${optionalString supportOldHostKeys ''
+          HostKeyAlgorithms +ssh-dss
+        ''}
       '';
 
     assertions = [{ assertion = if cfg.forwardX11 then cfgc.setXAuthLocation else true;

pkgs/tools/networking/openssh/default.nix

@@ -36,7 +36,16 @@ stdenv.mkDerivation rec {
       export NIX_LDFLAGS="$NIX_LDFLAGS -lgcc_s"
     '';
 
-  patches = [ ./locale_archive.patch ]
+  patches =
+    [ ./locale_archive.patch
+
+      # Fix "HostKeyAlgoritms +...", which we need to enable DSA
+      # host key support.
+      (fetchurl {
+        url = "https://pkgs.fedoraproject.org/cgit/rpms/openssh.git/plain/openssh-7.1p1-hostkeyalgorithms.patch?id=c98f5597250d6f9a8e8d96960beb6306d150ef0f";
+        sha256 = "029lzp9qv1af8wdm0wwj7qwjj1nimgsjj214jqm3amwz0857qgvp";
+      })
+    ]
     ++ optional withGssapiPatches gssapiSrc;
 
   buildInputs = [ zlib openssl libedit pkgconfig pam ]