refactor authentication logging

optionally record successful auth methods and public credentials
used in a file accessible to user sessions

feedback and ok markus@

1 files changed, 53 insertions, 1 deletions

diff --git a/usr.bin/ssh/session.c b/usr.bin/ssh/session.c
index 32046efdb6a..2f4ca7a37e0 100644
--- a/usr.bin/ssh/session.c
+++ b/usr.bin/ssh/session.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: session.c,v 1.289 2017/06/24 05:24:11 djm Exp $ */
+/* $OpenBSD: session.c,v 1.290 2017/06/24 06:34:38 djm Exp $ */
 /*
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
  *                    All rights reserved
@@ -85,6 +85,7 @@
 #endif
 #include "monitor_wrap.h"
 #include "sftp.h"
+#include "atomicio.h"
 
 #ifdef KRB5
 #include <kafs.h>
@@ -142,6 +143,9 @@ login_cap_t *lc;
 static int is_child = 0;
 static int in_chroot = 0;
 
+/* File containing userauth info, if ExposeAuthInfo set */
+static char *auth_info_file = NULL;
+
 /* Name and directory of socket for authentication agent forwarding. */
 static char *auth_sock_name = NULL;
 static char *auth_sock_dir = NULL;
@@ -231,6 +235,40 @@ display_loginmsg(void)
 	}
 }
 
+static void
+prepare_auth_info_file(struct passwd *pw, struct sshbuf *info)
+{
+	int fd = -1, success = 0;
+
+	if (!options.expose_userauth_info || info == NULL)
+		return;
+
+	temporarily_use_uid(pw);
+	auth_info_file = xstrdup("/tmp/sshauth.XXXXXXXXXXXXXXX");
+	if ((fd = mkstemp(auth_info_file)) == -1) {
+		error("%s: mkstemp: %s", __func__, strerror(errno));
+		goto out;
+	}
+	if (atomicio(vwrite, fd, sshbuf_mutable_ptr(info),
+	    sshbuf_len(info)) != sshbuf_len(info)) {
+		error("%s: write: %s", __func__, strerror(errno));
+		goto out;
+	}
+	if (close(fd) != 0) {
+		error("%s: close: %s", __func__, strerror(errno));
+		goto out;
+	}
+	success = 1;
+ out:
+	if (!success) {
+		if (fd != -1)
+			close(fd);
+		free(auth_info_file);
+		auth_info_file = NULL;
+	}
+	restore_uid();
+}
+
 void
 do_authenticated(Authctxt *authctxt)
 {
@@ -246,7 +284,10 @@ do_authenticated(Authctxt *authctxt)
 
 	auth_debug_send();
 
+	prepare_auth_info_file(authctxt->pw, authctxt->session_info);
+
 	do_authenticated2(authctxt);
+
 	do_cleanup(authctxt);
 }
 
@@ -845,6 +886,8 @@ do_setup_env(Session *s, const char *shell)
 	free(laddr);
 	child_set_env(&env, &envsize, "SSH_CONNECTION", buf);
 
+	if (auth_info_file != NULL)
+		child_set_env(&env, &envsize, "SSH_USER_AUTH", auth_info_file);
 	if (s->ttyfd != -1)
 		child_set_env(&env, &envsize, "SSH_TTY", s->tty);
 	if (s->term)
@@ -2147,6 +2190,15 @@ do_cleanup(Authctxt *authctxt)
 	/* remove agent socket */
 	auth_sock_cleanup_proc(authctxt->pw);
 
+	/* remove userauth info */
+	if (auth_info_file != NULL) {
+		temporarily_use_uid(authctxt->pw);
+		unlink(auth_info_file);
+		restore_uid();
+		free(auth_info_file);
+		auth_info_file = NULL;
+	}
+
 	/*
 	 * Cleanup ptys/utmp only if privsep is disabled,
 	 * or if running in monitor.