upstream commit

refactor authentication logging

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

feedback and ok markus@

Upstream-ID: 090b93036967015717b9a54fd0467875ae9d32fb

1 files changed, 132 insertions, 1 deletions

diff --git a/auth2.c b/auth2.c
index cb4c2fd5d..862e09960 100644
--- a/auth2.c
+++ b/auth2.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth2.c,v 1.142 2017/05/31 07:00:13 markus Exp $ */
+/* $OpenBSD: auth2.c,v 1.143 2017/06/24 06:34:38 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  *
@@ -30,6 +30,7 @@
 #include <sys/uio.h>
 
 #include <fcntl.h>
+#include <limits.h>
 #include <pwd.h>
 #include <stdarg.h>
 #include <string.h>
@@ -55,6 +56,7 @@
 #include "ssh-gss.h"
 #endif
 #include "monitor_wrap.h"
+#include "ssherr.h"
 
 /* import */
 extern ServerOptions options;
@@ -277,6 +279,7 @@ input_userauth_request(int type, u_int32_t seq, struct ssh *ssh)
         ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
 #endif
 
+        auth2_authctxt_reset_info(authctxt);
         authctxt->postponed = 0;
         authctxt->server_caused_failure = 0;
 
@@ -327,6 +330,10 @@ userauth_finish(struct ssh *ssh, int authenticated, const char *method,
         /* Log before sending the reply */
         auth_log(authctxt, authenticated, partial, method, submethod);
 
+        /* Update information exposed to session */
+        if (authenticated || partial)
+                auth2_update_session_info(authctxt, method, submethod);
+
         if (authctxt->postponed)
                 return;
 
@@ -624,4 +631,128 @@ auth2_update_methods_lists(Authctxt *authctxt, const char *method,
         return 0;
 }
 
+/* Reset method-specific information */
+void auth2_authctxt_reset_info(Authctxt *authctxt)
+{
+        sshkey_free(authctxt->auth_method_key);
+        free(authctxt->auth_method_info);
+        authctxt->auth_method_key = NULL;
+        authctxt->auth_method_info = NULL;
+}
+
+/* Record auth method-specific information for logs */
+void
+auth2_record_info(Authctxt *authctxt, const char *fmt, ...)
+{
+        va_list ap;
+        int i;
+
+        free(authctxt->auth_method_info);
+        authctxt->auth_method_info = NULL;
+
+        va_start(ap, fmt);
+        i = vasprintf(&authctxt->auth_method_info, fmt, ap);
+        va_end(ap);
+
+        if (i < 0 || authctxt->auth_method_info == NULL)
+                fatal("%s: vasprintf failed", __func__);
+}
+
+/*
+ * Records a public key used in authentication. This is used for logging
+ * and to ensure that the same key is not subsequently accepted again for
+ * multiple authentication.
+ */
+void
+auth2_record_key(Authctxt *authctxt, int authenticated,
+    const struct sshkey *key)
+{
+        struct sshkey **tmp, *dup;
+        int r;
+
+        if ((r = sshkey_demote(key, &dup)) != 0)
+                fatal("%s: copy key: %s", __func__, ssh_err(r));
+        sshkey_free(authctxt->auth_method_key);
+        authctxt->auth_method_key = dup;
+
+        if (!authenticated)
+                return;
+
+        /* If authenticated, make sure we don't accept this key again */
+        if ((r = sshkey_demote(key, &dup)) != 0)
+                fatal("%s: copy key: %s", __func__, ssh_err(r));
+        if (authctxt->nprev_keys >= INT_MAX ||
+            (tmp = recallocarray(authctxt->prev_keys, authctxt->nprev_keys,
+            authctxt->nprev_keys + 1, sizeof(*authctxt->prev_keys))) == NULL)
+                fatal("%s: reallocarray failed", __func__);
+        authctxt->prev_keys = tmp;
+        authctxt->prev_keys[authctxt->nprev_keys] = dup;
+        authctxt->nprev_keys++;
+
+}
+
+/* Checks whether a key has already been previously used for authentication */
+int
+auth2_key_already_used(Authctxt *authctxt, const struct sshkey *key)
+{
+        u_int i;
+        char *fp;
+
+        for (i = 0; i < authctxt->nprev_keys; i++) {
+                if (sshkey_equal_public(key, authctxt->prev_keys[i])) {
+                        fp = sshkey_fingerprint(authctxt->prev_keys[i],
+                            options.fingerprint_hash, SSH_FP_DEFAULT);
+                        debug3("%s: key already used: %s %s", __func__,
+                            sshkey_type(authctxt->prev_keys[i]),
+                            fp == NULL ? "UNKNOWN" : fp);
+                        free(fp);
+                        return 1;
+                }
+        }
+        return 0;
+}
+
+/*
+ * Updates authctxt->session_info with details of authentication. Should be
+ * whenever an authentication method succeeds.
+ */
+void
+auth2_update_session_info(Authctxt *authctxt, const char *method,
+    const char *submethod)
+{
+        int r;
+
+        if (authctxt->session_info == NULL) {
+                if ((authctxt->session_info = sshbuf_new()) == NULL)
+                        fatal("%s: sshbuf_new", __func__);
+        }
+
+        /* Append method[/submethod] */
+        if ((r = sshbuf_putf(authctxt->session_info, "%s%s%s",
+            method, submethod == NULL ? "" : "/",
+            submethod == NULL ? "" : submethod)) != 0)
+                fatal("%s: append method: %s", __func__, ssh_err(r));
+
+        /* Append key if present */
+        if (authctxt->auth_method_key != NULL) {
+                if ((r = sshbuf_put_u8(authctxt->session_info, ' ')) != 0 ||
+                    (r = sshkey_format_text(authctxt->auth_method_key,
+                    authctxt->session_info)) != 0)
+                        fatal("%s: append key: %s", __func__, ssh_err(r));
+        }
+
+        if (authctxt->auth_method_info != NULL) {
+                /* Ensure no ambiguity here */
+                if (strchr(authctxt->auth_method_info, '\n') != NULL)
+                        fatal("%s: auth_method_info contains \\n", __func__);
+                if ((r = sshbuf_put_u8(authctxt->session_info, ' ')) != 0 ||
+                    (r = sshbuf_putf(authctxt->session_info, "%s",
+                    authctxt->auth_method_info)) != 0) {
+                        fatal("%s: append method info: %s",
+                            __func__, ssh_err(r));
+                }
+        }
+        if ((r = sshbuf_put_u8(authctxt->session_info, '\n')) != 0)
+                fatal("%s: append: %s", __func__, ssh_err(r));
+}