Add a '%k' TOKEN that expands to the effective HostKey of the

destination.  This allows, eg, keeping host keys in individual files
using "UserKnownHostsFile ~/.ssh/known_hosts.d/%k".
bz#1654, ok djm@, jmc@ (man page bits)

4 files changed, 14 insertions, 4 deletions

diff --git a/usr.bin/ssh/ssh.c b/usr.bin/ssh/ssh.c
index 34def8473d8..701e8a8a21d 100644
--- a/usr.bin/ssh/ssh.c
+++ b/usr.bin/ssh/ssh.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh.c,v 1.532 2020/07/17 03:23:10 dtucker Exp $ */
+/* $OpenBSD: ssh.c,v 1.533 2020/07/17 03:43:42 dtucker Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -160,6 +160,7 @@ char *forward_agent_sock_path = NULL;
 /* Various strings used to to percent_expand() arguments */
 static char thishost[NI_MAXHOST], shorthost[NI_MAXHOST], portstr[NI_MAXSERV];
 static char uidstr[32], *host_arg, *conn_hash_hex;
+static const char *keyalias;
 
 /* socket address the host resolves to */
 struct sockaddr_storage hostaddr;
@@ -219,6 +220,7 @@ tilde_expand_paths(char **paths, u_int num_paths)
     "C", conn_hash_hex, \
     "L", shorthost, \
     "i", uidstr, \
+    "k", keyalias, \
     "l", thishost, \
     "n", host_arg, \
     "p", portstr
@@ -1359,6 +1361,7 @@ main(int ac, char **av)
 	snprintf(portstr, sizeof(portstr), "%d", options.port);
 	snprintf(uidstr, sizeof(uidstr), "%llu",
 	    (unsigned long long)pw->pw_uid);
+	keyalias = options.host_key_alias ? options.host_key_alias : host_arg;
 
 	conn_hash_hex = ssh_connection_hash(thishost, host, portstr,
 	    options.user);
diff --git a/usr.bin/ssh/ssh_config b/usr.bin/ssh/ssh_config
index 40f9d3924f1..fec5b080640 100644
--- a/usr.bin/ssh/ssh_config
+++ b/usr.bin/ssh/ssh_config
@@ -1,4 +1,4 @@
-#	$OpenBSD: ssh_config,v 1.34 2019/02/04 02:39:42 dtucker Exp $
+#	$OpenBSD: ssh_config,v 1.35 2020/07/17 03:43:42 dtucker Exp $
 
 # This is the ssh client system-wide configuration file.  See
 # ssh_config(5) for more information.  This file provides defaults for
@@ -41,3 +41,4 @@
 #   VisualHostKey no
 #   ProxyCommand ssh -q -W %h:%p gateway.example.com
 #   RekeyLimit 1G 1h
+#   UserKnownHostsFile ~/.ssh/known_hosts.d/%k
diff --git a/usr.bin/ssh/ssh_config.5 b/usr.bin/ssh/ssh_config.5
index 13ac08166db..0ddf4350107 100644
--- a/usr.bin/ssh/ssh_config.5
+++ b/usr.bin/ssh/ssh_config.5
@@ -33,7 +33,7 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.\" $OpenBSD: ssh_config.5,v 1.329 2020/07/17 03:23:10 dtucker Exp $
+.\" $OpenBSD: ssh_config.5,v 1.330 2020/07/17 03:43:42 dtucker Exp $
 .Dd $Mdocdate: July 17 2020 $
 .Dt SSH_CONFIG 5
 .Os
@@ -1851,6 +1851,9 @@ Local user's home directory.
 The remote hostname.
 .It %i
 The local user ID.
+.It %k
+The host key alias if specified, otherwise the orignal remote hostname given
+on the command line.
 .It %L
 The local hostname.
 .It %l
diff --git a/usr.bin/ssh/sshconnect.c b/usr.bin/ssh/sshconnect.c
index a598c3a4cb4..3b17241794b 100644
--- a/usr.bin/ssh/sshconnect.c
+++ b/usr.bin/ssh/sshconnect.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshconnect.c,v 1.329 2020/03/13 04:01:56 djm Exp $ */
+/* $OpenBSD: sshconnect.c,v 1.330 2020/07/17 03:43:42 dtucker Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -77,11 +77,14 @@ expand_proxy_command(const char *proxy_command, const char *user,
     const char *host, const char *host_arg, int port)
 {
 	char *tmp, *ret, strport[NI_MAXSERV];
+	const char *keyalias = options.host_key_alias ?
+	     options.host_key_alias : host_arg;
 
 	snprintf(strport, sizeof strport, "%d", port);
 	xasprintf(&tmp, "exec %s", proxy_command);
 	ret = percent_expand(tmp,
 	    "h", host,
+	    "k", keyalias,
 	    "n", host_arg,
 	    "p", strport,
 	    "r", options.user,