Various keepalive extensions

Add compatibility aliases for ProtocolKeepAlives and SetupTimeOut, supported
in previous versions of Debian's OpenSSH package but since superseded by
ServerAliveInterval.  (We're probably stuck with this bit for
compatibility.)

In batch mode, default ServerAliveInterval to five minutes.

Adjust documentation to match and to give some more advice on use of
keepalives.

Author: Ian Jackson <ian@chiark.greenend.org.uk>
Author: Matthew Vernon <matthew@debian.org>
Author: Colin Watson <cjwatson@debian.org>
Last-Update: 2016-12-26

Patch-Name: keepalive-extensions.patch

3 files changed, 34 insertions, 4 deletions

diff --git a/readconf.c b/readconf.c
index c1c3aae0d..3efba242f 100644
--- a/readconf.c
+++ b/readconf.c
@@ -173,6 +173,7 @@ typedef enum {
         oStreamLocalBindMask, oStreamLocalBindUnlink, oRevokedHostKeys,
         oFingerprintHash, oUpdateHostkeys, oHostbasedKeyTypes,
         oPubkeyAcceptedKeyTypes, oProxyJump,
+        oProtocolKeepAlives, oSetupTimeOut,
         oIgnoredUnknownOption, oDeprecated, oUnsupported
 } OpCodes;
 
@@ -308,6 +309,8 @@ static struct {
         { "pubkeyacceptedkeytypes", oPubkeyAcceptedKeyTypes },
         { "ignoreunknown", oIgnoreUnknown },
         { "proxyjump", oProxyJump },
+        { "protocolkeepalives", oProtocolKeepAlives },
+        { "setuptimeout", oSetupTimeOut },
 
         { NULL, oBadOption }
 };
@@ -1402,6 +1405,8 @@ parse_keytypes:
                 goto parse_flag;
 
         case oServerAliveInterval:
+        case oProtocolKeepAlives: /* Debian-specific compatibility alias */
+        case oSetupTimeOut:       /* Debian-specific compatibility alias */
                 intptr = &options->server_alive_interval;
                 goto parse_time;
 
@@ -2047,8 +2052,13 @@ fill_default_options(Options * options)
                 options->rekey_interval = 0;
         if (options->verify_host_key_dns == -1)
                 options->verify_host_key_dns = 0;
-        if (options->server_alive_interval == -1)
-                options->server_alive_interval = 0;
+        if (options->server_alive_interval == -1) {
+                /* in batch mode, default is 5mins */
+                if (options->batch_mode == 1)
+                        options->server_alive_interval = 300;
+                else
+                        options->server_alive_interval = 0;
+        }
         if (options->server_alive_count_max == -1)
                 options->server_alive_count_max = 3;
         if (options->control_master == -1)
diff --git a/ssh_config.5 b/ssh_config.5
index a7703fc77..a0457314c 100644
--- a/ssh_config.5
+++ b/ssh_config.5
@@ -250,8 +250,12 @@ Valid arguments are
 If set to
 .Cm yes ,
 passphrase/password querying will be disabled.
+In addition, the
+.Cm ServerAliveInterval
+option will be set to 300 seconds by default (Debian-specific).
 This option is useful in scripts and other batch jobs where no user
-is present to supply the password.
+is present to supply the password,
+and where it is desirable to detect a broken network swiftly.
 The argument must be
 .Cm yes
 or
@@ -1485,7 +1489,14 @@ from the server,
 will send a message through the encrypted
 channel to request a response from the server.
 The default
-is 0, indicating that these messages will not be sent to the server.
+is 0, indicating that these messages will not be sent to the server,
+or 300 if the
+.Cm BatchMode
+option is set (Debian-specific).
+.Cm ProtocolKeepAlives
+and
+.Cm SetupTimeOut
+are Debian-specific compatibility aliases for this option.
 .It Cm StreamLocalBindMask
 Sets the octal file creation mode mask
 .Pq umask
@@ -1544,6 +1555,12 @@ Specifies whether the system should send TCP keepalive messages to the
 other side.
 If they are sent, death of the connection or crash of one
 of the machines will be properly noticed.
+This option only uses TCP keepalives (as opposed to using ssh level
+keepalives), so takes a long time to notice when the connection dies.
+As such, you probably want
+the
+.Cm ServerAliveInterval
+option as well.
 However, this means that
 connections will die if the route is down temporarily, and some people
 find it annoying.
diff --git a/sshd_config.5 b/sshd_config.5
index dd765b391..283ba8896 100644
--- a/sshd_config.5
+++ b/sshd_config.5
@@ -1427,6 +1427,9 @@ This avoids infinitely hanging sessions.
 .Pp
 To disable TCP keepalive messages, the value should be set to
 .Cm no .
+.Pp
+This option was formerly called
+.Cm KeepAlive .
 .It Cm TrustedUserCAKeys
 Specifies a file containing public keys of certificate authorities that are
 trusted to sign user certificates for authentication, or