From ed4ce82dbfa8a3a3c8ea6fa0db113c71e234416c Mon Sep 17 00:00:00 2001 From: "djm@openbsd.org" Date: Wed, 13 Jan 2016 23:04:47 +0000 Subject: [PATCH] upstream commit eliminate fallback from untrusted X11 forwarding to trusted forwarding when the X server disables the SECURITY extension; Reported by Thomas Hoger; ok deraadt@ Upstream-ID: f76195bd2064615a63ef9674a0e4096b0713f938 Upstream-Status: Backport CVE: CVE-2016-1907 [YOCTO #8935] Signed-off-by: Armin Kuster --- clientloop.c | 114 ++++++++++++++++++++++++++++++++++++----------------------- clientloop.h | 4 +-- mux.c | 22 ++++++------ ssh.c | 23 +++++------- 4 files changed, 93 insertions(+), 70 deletions(-) Index: openssh-7.1p2/clientloop.c =================================================================== --- openssh-7.1p2.orig/clientloop.c +++ openssh-7.1p2/clientloop.c @@ -1,4 +1,4 @@ -/* $OpenBSD: clientloop.c,v 1.276 2015/10/20 03:36:35 mmcc Exp $ */ +/* $OpenBSD: clientloop.c,v 1.279 2016/01/13 23:04:47 djm Exp $ */ /* * Author: Tatu Ylonen * Copyright (c) 1995 Tatu Ylonen , Espoo, Finland @@ -288,6 +288,9 @@ client_x11_display_valid(const char *dis { size_t i, dlen; + if (display == NULL) + return 0; + dlen = strlen(display); for (i = 0; i < dlen; i++) { if (!isalnum((u_char)display[i]) && @@ -301,34 +304,33 @@ client_x11_display_valid(const char *dis #define SSH_X11_PROTO "MIT-MAGIC-COOKIE-1" #define X11_TIMEOUT_SLACK 60 -void +int client_x11_get_proto(const char *display, const char *xauth_path, u_int trusted, u_int timeout, char **_proto, char **_data) { - char cmd[1024]; - char line[512]; - char xdisplay[512]; + char cmd[1024], line[512], xdisplay[512]; + char xauthfile[PATH_MAX], xauthdir[PATH_MAX]; static char proto[512], data[512]; FILE *f; - int got_data = 0, generated = 0, do_unlink = 0, i; - char xauthdir[PATH_MAX] = "", xauthfile[PATH_MAX] = ""; + int got_data = 0, generated = 0, do_unlink = 0, i, r; struct stat st; u_int now, x11_timeout_real; *_proto = proto; *_data = data; - proto[0] = data[0] = '\0'; + proto[0] = data[0] = xauthfile[0] = xauthdir[0] = '\0'; - if (xauth_path == NULL ||(stat(xauth_path, &st) == -1)) { - debug("No xauth program."); - } else if (!client_x11_display_valid(display)) { - logit("DISPLAY '%s' invalid, falling back to fake xauth data", + if (!client_x11_display_valid(display)) { + logit("DISPLAY \"%s\" invalid; disabling X11 forwarding", display); - } else { - if (display == NULL) { - debug("x11_get_proto: DISPLAY not set"); - return; - } + return -1; + } + if (xauth_path != NULL && stat(xauth_path, &st) == -1) { + debug("No xauth program."); + xauth_path = NULL; + } + + if (xauth_path != NULL) { /* * Handle FamilyLocal case where $DISPLAY does * not match an authorization entry. For this we @@ -337,43 +339,60 @@ client_x11_get_proto(const char *display * is not perfect. */ if (strncmp(display, "localhost:", 10) == 0) { - snprintf(xdisplay, sizeof(xdisplay), "unix:%s", - display + 10); + if ((r = snprintf(xdisplay, sizeof(xdisplay), "unix:%s", + display + 10)) < 0 || + (size_t)r >= sizeof(xdisplay)) { + error("%s: display name too long", __func__); + return -1; + } display = xdisplay; } if (trusted == 0) { - mktemp_proto(xauthdir, PATH_MAX); /* + * Generate an untrusted X11 auth cookie. + * * The authentication cookie should briefly outlive * ssh's willingness to forward X11 connections to * avoid nasty fail-open behaviour in the X server. */ + mktemp_proto(xauthdir, sizeof(xauthdir)); + if (mkdtemp(xauthdir) == NULL) { + error("%s: mkdtemp: %s", + __func__, strerror(errno)); + return -1; + } + do_unlink = 1; + if ((r = snprintf(xauthfile, sizeof(xauthfile), + "%s/xauthfile", xauthdir)) < 0 || + (size_t)r >= sizeof(xauthfile)) { + error("%s: xauthfile path too long", __func__); + unlink(xauthfile); + rmdir(xauthdir); + return -1; + } + 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", - xauthdir); - snprintf(cmd, sizeof(cmd), - "%s -f %s generate %s " SSH_X11_PROTO - " untrusted timeout %u 2>" _PATH_DEVNULL, - xauth_path, xauthfile, display, - x11_timeout_real); - debug2("x11_get_proto: %s", cmd); - 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; + if ((r = snprintf(cmd, sizeof(cmd), + "%s -f %s generate %s " SSH_X11_PROTO + " untrusted timeout %u 2>" _PATH_DEVNULL, + xauth_path, xauthfile, display, + x11_timeout_real)) < 0 || + (size_t)r >= sizeof(cmd)) + fatal("%s: cmd too long", __func__); + debug2("%s: %s", __func__, cmd); + 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; } /* @@ -395,9 +414,7 @@ client_x11_get_proto(const char *display got_data = 1; if (f) pclose(f); - } else - error("Warning: untrusted X11 forwarding setup failed: " - "xauth key data not generated"); + } } if (do_unlink) { @@ -405,6 +422,13 @@ client_x11_get_proto(const char *display rmdir(xauthdir); } + /* Don't fall back to fake X11 data for untrusted forwarding */ + if (!trusted && !got_data) { + error("Warning: untrusted X11 forwarding setup failed: " + "xauth key data not generated"); + return -1; + } + /* * If we didn't get authentication data, just make up some * data. The forwarding code will check the validity of the @@ -427,6 +451,8 @@ client_x11_get_proto(const char *display rnd >>= 8; } } + + return 0; } /* Index: openssh-7.1p2/clientloop.h =================================================================== --- openssh-7.1p2.orig/clientloop.h +++ openssh-7.1p2/clientloop.h @@ -1,4 +1,4 @@ -/* $OpenBSD: clientloop.h,v 1.31 2013/06/02 23:36:29 dtucker Exp $ */ +/* $OpenBSD: clientloop.h,v 1.32 2016/01/13 23:04:47 djm Exp $ */ /* * Author: Tatu Ylonen @@ -39,7 +39,7 @@ /* Client side main loop for the interactive session. */ int client_loop(int, int, int); -void client_x11_get_proto(const char *, const char *, u_int, u_int, +int client_x11_get_proto(const char *, const char *, u_int, u_int, char **, char **); void client_global_request_reply_fwd(int, u_int32_t, void *); void client_session2_setup(int, int, int, const char *, struct termios *, Index: openssh-7.1p2/mux.c =================================================================== --- openssh-7.1p2.orig/mux.c +++ openssh-7.1p2/mux.c @@ -1,4 +1,4 @@ -/* $OpenBSD: mux.c,v 1.54 2015/08/19 23:18:26 djm Exp $ */ +/* $OpenBSD: mux.c,v 1.58 2016/01/13 23:04:47 djm Exp $ */ /* * Copyright (c) 2002-2008 Damien Miller * @@ -1354,16 +1354,18 @@ mux_session_confirm(int id, int success, char *proto, *data; /* Get reasonable local authentication information. */ - client_x11_get_proto(display, options.xauth_location, + if (client_x11_get_proto(display, options.xauth_location, options.forward_x11_trusted, options.forward_x11_timeout, - &proto, &data); - /* Request forwarding with authentication spoofing. */ - debug("Requesting X11 forwarding with authentication " - "spoofing."); - x11_request_forwarding_with_spoofing(id, display, proto, - data, 1); - client_expect_confirm(id, "X11 forwarding", CONFIRM_WARN); - /* XXX exit_on_forward_failure */ + &proto, &data) == 0) { + /* Request forwarding with authentication spoofing. */ + debug("Requesting X11 forwarding with authentication " + "spoofing."); + x11_request_forwarding_with_spoofing(id, display, proto, + data, 1); + /* XXX exit_on_forward_failure */ + client_expect_confirm(id, "X11 forwarding", + CONFIRM_WARN); + } } if (cctx->want_agent_fwd && options.forward_agent) { Index: openssh-7.1p2/ssh.c =================================================================== --- openssh-7.1p2.orig/ssh.c +++ openssh-7.1p2/ssh.c @@ -1,4 +1,4 @@ -/* $OpenBSD: ssh.c,v 1.420 2015/07/30 00:01:34 djm Exp $ */ +/* $OpenBSD: ssh.c,v 1.433 2016/01/13 23:04:47 djm Exp $ */ /* * Author: Tatu Ylonen * Copyright (c) 1995 Tatu Ylonen , Espoo, Finland @@ -1604,6 +1604,7 @@ ssh_session(void) struct winsize ws; char *cp; const char *display; + char *proto = NULL, *data = NULL; /* Enable compression if requested. */ if (options.compression) { @@ -1674,13 +1675,9 @@ ssh_session(void) display = getenv("DISPLAY"); if (display == NULL && options.forward_x11) debug("X11 forwarding requested but DISPLAY not set"); - if (options.forward_x11 && display != NULL) { - char *proto, *data; - /* Get reasonable local authentication information. */ - client_x11_get_proto(display, options.xauth_location, - options.forward_x11_trusted, - options.forward_x11_timeout, - &proto, &data); + if (options.forward_x11 && client_x11_get_proto(display, + options.xauth_location, options.forward_x11_trusted, + options.forward_x11_timeout, &proto, &data) == 0) { /* Request forwarding with authentication spoofing. */ debug("Requesting X11 forwarding with authentication " "spoofing."); @@ -1770,6 +1767,7 @@ ssh_session2_setup(int id, int success, extern char **environ; const char *display; int interactive = tty_flag; + char *proto = NULL, *data = NULL; if (!success) return; /* No need for error message, channels code sens one */ @@ -1777,12 +1775,9 @@ ssh_session2_setup(int id, int success, display = getenv("DISPLAY"); if (display == NULL && options.forward_x11) debug("X11 forwarding requested but DISPLAY not set"); - if (options.forward_x11 && display != NULL) { - char *proto, *data; - /* Get reasonable local authentication information. */ - client_x11_get_proto(display, options.xauth_location, - options.forward_x11_trusted, - options.forward_x11_timeout, &proto, &data); + if (options.forward_x11 && client_x11_get_proto(display, + options.xauth_location, options.forward_x11_trusted, + options.forward_x11_timeout, &proto, &data) == 0) { /* Request forwarding with authentication spoofing. */ debug("Requesting X11 forwarding with authentication " "spoofing.");