Allow forwarding a different agent socket to the path specified by

$SSH_AUTH_SOCK, by extending the existing ForwardAgent option to
accepting an explicit path or the name of an environment variable
in addition to yes/no.

Patch by Eric Chiang, manpage by me; ok markus@

1 files changed, 33 insertions, 1 deletions

diff --git a/usr.bin/ssh/ssh.c b/usr.bin/ssh/ssh.c
index 6454e59d67e..255ab192fbd 100644
--- a/usr.bin/ssh/ssh.c
+++ b/usr.bin/ssh/ssh.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh.c,v 1.509 2019/11/18 16:10:05 naddy Exp $ */
+/* $OpenBSD: ssh.c,v 1.510 2019/12/21 02:19:13 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -152,6 +152,12 @@ char *config = NULL;
  */
 char *host;
 
+/*
+ * A config can specify a path to forward, overriding SSH_AUTH_SOCK. If this is
+ * not NULL, forward the socket at this path instead.
+ */
+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;
@@ -1471,6 +1477,32 @@ main(int ac, char **av)
 		}
 	}
 
+	if (options.forward_agent && (options.forward_agent_sock_path != NULL)) {
+		p = tilde_expand_filename(options.forward_agent_sock_path, getuid());
+		cp = percent_expand(p,
+		    "d", pw->pw_dir,
+		    "h", host,
+		    "i", uidstr,
+		    "l", thishost,
+		    "r", options.user,
+		    "u", pw->pw_name,
+		    (char *)NULL);
+		free(p);
+
+		if (cp[0] == '$') {
+			if (!valid_env_name(cp + 1)) {
+				fatal("Invalid ForwardAgent environment variable name %s", cp);
+			}
+			if ((p = getenv(cp + 1)) != NULL)
+				forward_agent_sock_path = p;
+			else
+				options.forward_agent = 0;
+			free(cp);
+		} else {
+			forward_agent_sock_path = cp;
+		}
+	}
+
 	/* Expand ~ in known host file names. */
 	tilde_expand_paths(options.system_hostfiles,
 	    options.num_system_hostfiles);