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authordjm@openbsd.org <djm@openbsd.org>2015-07-01 02:26:31 +0000
committerDamien Miller <djm@mindrot.org>2015-07-01 12:29:43 +1000
commit1bf477d3cdf1a864646d59820878783d42357a1d (patch)
tree51d4c6538c262177bf76316eba414a6202964b36
parent47aa7a0f8551b471fcae0447c1d78464f6dba869 (diff)
upstream commit
better refuse ForwardX11Trusted=no connections attempted after ForwardX11Timeout expires; reported by Jann Horn Upstream-ID: bf0fddadc1b46a0334e26c080038313b4b6dea21
-rw-r--r--channels.c18
-rw-r--r--channels.h3
-rw-r--r--clientloop.c29
3 files changed, 40 insertions, 10 deletions
diff --git a/channels.c b/channels.c
index 3fe836aa..a84b487e 100644
--- a/channels.c
+++ b/channels.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: channels.c,v 1.346 2015/06/30 05:25:07 djm Exp $ */
+/* $OpenBSD: channels.c,v 1.347 2015/07/01 02:26:31 djm Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -161,6 +161,9 @@ static char *x11_saved_proto = NULL;
static char *x11_saved_data = NULL;
static u_int x11_saved_data_len = 0;
+/* Deadline after which all X11 connections are refused */
+static u_int x11_refuse_time;
+
/*
* Fake X11 authentication data. This is what the server will be sending us;
* we should replace any occurrences of this by the real data.
@@ -912,6 +915,13 @@ x11_open_helper(Buffer *b)
u_char *ucp;
u_int proto_len, data_len;
+ /* Is this being called after the refusal deadline? */
+ if (x11_refuse_time != 0 && (u_int)monotime() >= x11_refuse_time) {
+ verbose("Rejected X11 connection after ForwardX11Timeout "
+ "expired");
+ return -1;
+ }
+
/* Check if the fixed size part of the packet is in buffer. */
if (buffer_len(b) < 12)
return 0;
@@ -1483,6 +1493,12 @@ channel_set_reuseaddr(int fd)
error("setsockopt SO_REUSEADDR fd %d: %s", fd, strerror(errno));
}
+void
+channel_set_x11_refuse_time(u_int refuse_time)
+{
+ x11_refuse_time = refuse_time;
+}
+
/*
* This socket is listening for connections to a forwarded TCP/IP port.
*/
diff --git a/channels.h b/channels.h
index b9b48602..9d76c9d2 100644
--- a/channels.h
+++ b/channels.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: channels.h,v 1.117 2015/05/08 06:45:13 djm Exp $ */
+/* $OpenBSD: channels.h,v 1.118 2015/07/01 02:26:31 djm Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -284,6 +284,7 @@ int permitopen_port(const char *);
/* x11 forwarding */
+void channel_set_x11_refuse_time(u_int);
int x11_connect_display(void);
int x11_create_display_inet(int, int, int, u_int *, int **);
int x11_input_open(int, u_int32_t, void *);
diff --git a/clientloop.c b/clientloop.c
index 040deb99..dc0e557a 100644
--- a/clientloop.c
+++ b/clientloop.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: clientloop.c,v 1.273 2015/05/04 06:10:48 djm Exp $ */
+/* $OpenBSD: clientloop.c,v 1.274 2015/07/01 02:26:31 djm Exp $ */
/*
* Author: Tatu Ylonen <ylo@cs.hut.fi>
* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -163,7 +163,7 @@ static int connection_in; /* Connection to server (input). */
static int connection_out; /* Connection to server (output). */
static int need_rekeying; /* Set to non-zero if rekeying is requested. */
static int session_closed; /* In SSH2: login session closed. */
-static int x11_refuse_time; /* If >0, refuse x11 opens after this time. */
+static u_int x11_refuse_time; /* If >0, refuse x11 opens after this time. */
static void client_init_dispatch(void);
int session_ident = -1;
@@ -298,7 +298,8 @@ client_x11_display_valid(const char *display)
return 1;
}
-#define SSH_X11_PROTO "MIT-MAGIC-COOKIE-1"
+#define SSH_X11_PROTO "MIT-MAGIC-COOKIE-1"
+#define X11_TIMEOUT_SLACK 60
void
client_x11_get_proto(const char *display, const char *xauth_path,
u_int trusted, u_int timeout, char **_proto, char **_data)
@@ -311,7 +312,7 @@ client_x11_get_proto(const char *display, const char *xauth_path,
int got_data = 0, generated = 0, do_unlink = 0, i;
char *xauthdir, *xauthfile;
struct stat st;
- u_int now;
+ u_int now, x11_timeout_real;
xauthdir = xauthfile = NULL;
*_proto = proto;
@@ -344,6 +345,15 @@ client_x11_get_proto(const char *display, const char *xauth_path,
xauthdir = xmalloc(PATH_MAX);
xauthfile = xmalloc(PATH_MAX);
mktemp_proto(xauthdir, PATH_MAX);
+ /*
+ * The authentication cookie should briefly outlive
+ * ssh's willingness to forward X11 connections to
+ * avoid nasty fail-open behaviour in the X server.
+ */
+ if (timeout >= UINT_MAX - X11_TIMEOUT_SLACK)
+ x11_timeout_real = UINT_MAX;
+ else
+ x11_timeout_real = timeout + X11_TIMEOUT_SLACK;
if (mkdtemp(xauthdir) != NULL) {
do_unlink = 1;
snprintf(xauthfile, PATH_MAX, "%s/xauthfile",
@@ -351,17 +361,20 @@ client_x11_get_proto(const char *display, const char *xauth_path,
snprintf(cmd, sizeof(cmd),
"%s -f %s generate %s " SSH_X11_PROTO
" untrusted timeout %u 2>" _PATH_DEVNULL,
- xauth_path, xauthfile, display, timeout);
+ xauth_path, xauthfile, display,
+ x11_timeout_real);
debug2("x11_get_proto: %s", cmd);
- if (system(cmd) == 0)
- generated = 1;
if (x11_refuse_time == 0) {
now = monotime() + 1;
if (UINT_MAX - timeout < now)
x11_refuse_time = UINT_MAX;
else
x11_refuse_time = now + timeout;
+ channel_set_x11_refuse_time(
+ x11_refuse_time);
}
+ if (system(cmd) == 0)
+ generated = 1;
}
}
@@ -1889,7 +1902,7 @@ client_request_x11(const char *request_type, int rchan)
"malicious server.");
return NULL;
}
- if (x11_refuse_time != 0 && monotime() >= x11_refuse_time) {
+ if (x11_refuse_time != 0 && (u_int)monotime() >= x11_refuse_time) {
verbose("Rejected X11 connection after ForwardX11Timeout "
"expired");
return NULL;