Various Debian-specific configuration changes

ssh: Enable ForwardX11Trusted, returning to earlier semantics which cause
fewer problems with existing setups (http://bugs.debian.org/237021).

ssh: Set 'SendEnv LANG LC_*' by default (http://bugs.debian.org/264024).

ssh: Enable HashKnownHosts by default to try to limit the spread of ssh
worms.

ssh: Enable GSSAPIAuthentication and disable GSSAPIDelegateCredentials by
default.

Document all of this, along with several sshd defaults set in
debian/openssh-server.postinst.

Author: Russ Allbery <rra@debian.org>
Forwarded: not-needed
Last-Update: 2015-12-07

Patch-Name: debian-config.patch

6 files changed, 72 insertions, 4 deletions

diff --git a/readconf.c b/readconf.c
index f6b4c8f1e..5cd51f3e6 100644
--- a/readconf.c
+++ b/readconf.c
@@ -1928,7 +1928,7 @@ fill_default_options(Options * options)
         if (options->forward_x11 == -1)
                 options->forward_x11 = 0;
         if (options->forward_x11_trusted == -1)
-                options->forward_x11_trusted = 0;
+                options->forward_x11_trusted = 1;
         if (options->forward_x11_timeout == -1)
                 options->forward_x11_timeout = 1200;
         /*
diff --git a/ssh.1 b/ssh.1
index 22e56a7b9..6aa57c462 100644
--- a/ssh.1
+++ b/ssh.1
@@ -785,6 +785,16 @@ directive in
 .Xr ssh_config 5
 for more information.
 .Pp
+(Debian-specific: X11 forwarding is not subjected to X11 SECURITY extension
+restrictions by default, because too many programs currently crash in this
+mode.
+Set the
+.Cm ForwardX11Trusted
+option to
+.Dq no
+to restore the upstream behaviour.
+This may change in future depending on client-side improvements.)
+.Pp
 .It Fl x
 Disables X11 forwarding.
 .Pp
@@ -793,6 +803,17 @@ Enables trusted X11 forwarding.
 Trusted X11 forwardings are not subjected to the X11 SECURITY extension
 controls.
 .Pp
+(Debian-specific: This option does nothing in the default configuration: it
+is equivalent to
+.Dq Cm ForwardX11Trusted No yes ,
+which is the default as described above.
+Set the
+.Cm ForwardX11Trusted
+option to
+.Dq no
+to restore the upstream behaviour.
+This may change in future depending on client-side improvements.)
+.Pp
 .It Fl y
 Send log information using the
 .Xr syslog 3
diff --git a/ssh_config b/ssh_config
index 4e879cd20..5190b06b1 100644
--- a/ssh_config
+++ b/ssh_config
@@ -17,9 +17,10 @@
 # list of available options, their meanings and defaults, please see the
 # ssh_config(5) man page.
 
-# Host *
+Host *
 #   ForwardAgent no
 #   ForwardX11 no
+#   ForwardX11Trusted yes
 #   RhostsRSAAuthentication no
 #   RSAAuthentication yes
 #   PasswordAuthentication yes
@@ -50,3 +51,7 @@
 #   VisualHostKey no
 #   ProxyCommand ssh -q -W %h:%p gateway.example.com
 #   RekeyLimit 1G 1h
+    SendEnv LANG LC_*
+    HashKnownHosts yes
+    GSSAPIAuthentication yes
+    GSSAPIDelegateCredentials no
diff --git a/ssh_config.5 b/ssh_config.5
index 30c97a9b9..c96725862 100644
--- a/ssh_config.5
+++ b/ssh_config.5
@@ -74,6 +74,22 @@ Since the first obtained value for each parameter is used, more
 host-specific declarations should be given near the beginning of the
 file, and general defaults at the end.
 .Pp
+Note that the Debian
+.Ic openssh-client
+package sets several options as standard in
+.Pa /etc/ssh/ssh_config
+which are not the default in
+.Xr ssh 1 :
+.Pp
+.Bl -bullet -offset indent -compact
+.It
+.Cm SendEnv No LANG LC_*
+.It
+.Cm HashKnownHosts No yes
+.It
+.Cm GSSAPIAuthentication No yes
+.El
+.Pp
 The configuration file has the following format:
 .Pp
 Empty lines and lines starting with
@@ -799,7 +815,8 @@ token used for the session will be set to expire after 20 minutes.
 Remote clients will be refused access after this time.
 .Pp
 The default is
-.Dq no .
+.Dq yes
+(Debian-specific).
 .Pp
 See the X11 SECURITY extension specification for full details on
 the restrictions imposed on untrusted clients.
diff --git a/sshd_config b/sshd_config
index 3fe3e017e..ec8ff8f19 100644
--- a/sshd_config
+++ b/sshd_config
@@ -124,7 +124,7 @@ AuthorizedKeysFile	.ssh/authorized_keys
 #Banner none
 
 # override default of no subsystems
-Subsystem       sftp    /usr/libexec/sftp-server
+Subsystem       sftp    /usr/lib/openssh/sftp-server
 
 # Example of overriding settings on a per-user basis
 #Match User anoncvs
diff --git a/sshd_config.5 b/sshd_config.5
index b2b349e1b..79f2d611f 100644
--- a/sshd_config.5
+++ b/sshd_config.5
@@ -57,6 +57,31 @@ Arguments may optionally be enclosed in double quotes
 .Pq \&"
 in order to represent arguments containing spaces.
 .Pp
+Note that the Debian
+.Ic openssh-server
+package sets several options as standard in
+.Pa /etc/ssh/sshd_config
+which are not the default in
+.Xr sshd 8 .
+The exact list depends on whether the package was installed fresh or
+upgraded from various possible previous versions, but includes at least the
+following:
+.Pp
+.Bl -bullet -offset indent -compact
+.It
+.Cm ChallengeResponseAuthentication No no
+.It
+.Cm X11Forwarding No yes
+.It
+.Cm PrintMotd No no
+.It
+.Cm AcceptEnv No LANG LC_*
+.It
+.Cm Subsystem No sftp /usr/lib/openssh/sftp-server
+.It
+.Cm UsePAM No yes
+.El
+.Pp
 The possible
 keywords and their meanings are as follows (note that
 keywords are case-insensitive and arguments are case-sensitive):