diff -up openssh-7.4p1/channels.c.x11max openssh-7.4p1/channels.c
--- openssh-7.4p1/channels.c.x11max 2017-02-09 12:49:04.690996627 +0100
+++ openssh-7.4p1/channels.c 2017-02-09 12:49:04.744996547 +0100
@@ -152,8 +152,8 @@ static int all_opens_permitted = 0;
/* -- X11 forwarding */
-/* Maximum number of fake X11 displays to try. */
-#define MAX_DISPLAYS 1000
+/* Minimum port number for X11 forwarding */
+#define X11_PORT_MIN 6000
/* Saved X11 local (client) display. */
static char *x11_saved_display = NULL;
@@ -4228,7 +4228,8 @@ channel_send_window_changes(void)
*/
int
x11_create_display_inet(int x11_display_offset, int x11_use_localhost,
- int single_connection, u_int *display_numberp, int **chanids)
+ int x11_max_displays, int single_connection, u_int *display_numberp,
+ int **chanids)
{
Channel *nc = NULL;
int display_number, sock;
@@ -4240,10 +4241,15 @@ x11_create_display_inet(int x11_display_
if (chanids == NULL)
return -1;
+ /* Try to bind ports starting at 6000+X11DisplayOffset */
+ x11_max_displays = x11_max_displays + x11_display_offset;
+
for (display_number = x11_display_offset;
- display_number < MAX_DISPLAYS;
+ display_number < x11_max_displays;
display_number++) {
- port = 6000 + display_number;
+ port = X11_PORT_MIN + display_number;
+ if (port < X11_PORT_MIN) /* overflow */
+ break;
memset(&hints, 0, sizeof(hints));
hints.ai_family = IPv4or6;
hints.ai_flags = x11_use_localhost ? 0: AI_PASSIVE;
@@ -4295,7 +4301,7 @@ x11_create_display_inet(int x11_display_
if (num_socks > 0)
break;
}
- if (display_number >= MAX_DISPLAYS) {
+ if (display_number >= x11_max_displays || port < X11_PORT_MIN ) {
error("Failed to allocate internet-domain X11 display socket.");
return -1;
}
@@ -4441,7 +4447,7 @@ x11_connect_display(void)
memset(&hints, 0, sizeof(hints));
hints.ai_family = IPv4or6;
hints.ai_socktype = SOCK_STREAM;
- snprintf(strport, sizeof strport, "%u", 6000 + display_number);
+ snprintf(strport, sizeof strport, "%u", X11_PORT_MIN + display_number);
if ((gaierr = getaddrinfo(buf, strport, &hints, &aitop)) != 0) {
error("%.100s: unknown host. (%s)", buf,
ssh_gai_strerror(gaierr));
@@ -4457,7 +4463,7 @@ x11_connect_display(void)
/* Connect it to the display. */
if (connect(sock, ai->ai_addr, ai->ai_addrlen) < 0) {
debug2("connect %.100s port %u: %.100s", buf,
- 6000 + display_number, strerror(errno));
+ X11_PORT_MIN + display_number, strerror(errno));
close(sock);
continue;
}
@@ -4466,8 +4472,8 @@ x11_connect_display(void)
}
freeaddrinfo(aitop);
if (!ai) {
- error("connect %.100s port %u: %.100s", buf, 6000 + display_number,
- strerror(errno));
+ error("connect %.100s port %u: %.100s", buf,
+ X11_PORT_MIN + display_number, strerror(errno));
return -1;
}
set_nodelay(sock);
diff -up openssh-7.4p1/channels.h.x11max openssh-7.4p1/channels.h
--- openssh-7.4p1/channels.h.x11max 2017-02-09 12:49:04.744996547 +0100
+++ openssh-7.4p1/channels.h 2017-02-09 12:49:50.230929693 +0100
@@ -293,7 +293,7 @@ int permitopen_port(const char *);
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_create_display_inet(int, int, int, int, u_int *, int **);
int x11_input_open(int, u_int32_t, void *);
void x11_request_forwarding_with_spoofing(int, const char *, const char *,
const char *, int);
diff -up openssh-7.4p1/servconf.c.x11max openssh-7.4p1/servconf.c
--- openssh-7.4p1/servconf.c.x11max 2017-02-09 12:49:04.741996552 +0100
+++ openssh-7.4p1/servconf.c 2017-02-09 12:51:03.167822492 +0100
@@ -94,6 +94,7 @@ initialize_server_options(ServerOptions
options->print_lastlog = -1;
options->x11_forwarding = -1;
options->x11_display_offset = -1;
+ options->x11_max_displays = -1;
options->x11_use_localhost = -1;
options->permit_tty = -1;
options->permit_user_rc = -1;
@@ -242,6 +243,8 @@ fill_default_server_options(ServerOption
options->x11_forwarding = 0;
if (options->x11_display_offset == -1)
options->x11_display_offset = 10;
+ if (options->x11_max_displays == -1)
+ options->x11_max_displays = DEFAULT_MAX_DISPLAYS;
if (options->x11_use_localhost == -1)
options->x11_use_localhost = 1;
if (options->xauth_location == NULL)
@@ -416,7 +419,7 @@ typedef enum {
sPasswordAuthentication, sKbdInteractiveAuthentication,
sListenAddress, sAddressFamily,
sPrintMotd, sPrintLastLog, sIgnoreRhosts,
- sX11Forwarding, sX11DisplayOffset, sX11UseLocalhost,
+ sX11Forwarding, sX11DisplayOffset, sX11MaxDisplays, sX11UseLocalhost,
sPermitTTY, sStrictModes, sEmptyPasswd, sTCPKeepAlive,
sPermitUserEnvironment, sAllowTcpForwarding, sCompression,
sRekeyLimit, sAllowUsers, sDenyUsers, sAllowGroups, sDenyGroups,
@@ -537,6 +540,7 @@ static struct {
{ "ignoreuserknownhosts", sIgnoreUserKnownHosts, SSHCFG_GLOBAL },
{ "x11forwarding", sX11Forwarding, SSHCFG_ALL },
{ "x11displayoffset", sX11DisplayOffset, SSHCFG_ALL },
+ { "x11maxdisplays", sX11MaxDisplays, SSHCFG_ALL },
{ "x11uselocalhost", sX11UseLocalhost, SSHCFG_ALL },
{ "xauthlocation", sXAuthLocation, SSHCFG_GLOBAL },
{ "strictmodes", sStrictModes, SSHCFG_GLOBAL },
@@ -1313,6 +1317,10 @@ process_server_config_line(ServerOptions
*intptr = value;
break;
+ case sX11MaxDisplays:
+ intptr = &options->x11_max_displays;
+ goto parse_int;
+
case sX11UseLocalhost:
intptr = &options->x11_use_localhost;
goto parse_flag;
@@ -2060,6 +2068,7 @@ copy_set_server_options(ServerOptions *d
M_CP_INTOPT(fwd_opts.streamlocal_bind_unlink);
M_CP_INTOPT(x11_display_offset);
M_CP_INTOPT(x11_forwarding);
+ M_CP_INTOPT(x11_max_displays);
M_CP_INTOPT(x11_use_localhost);
M_CP_INTOPT(permit_tty);
M_CP_INTOPT(permit_user_rc);
@@ -2312,6 +2321,7 @@ dump_config(ServerOptions *o)
#endif
dump_cfg_int(sLoginGraceTime, o->login_grace_time);
dump_cfg_int(sX11DisplayOffset, o->x11_display_offset);
+ dump_cfg_int(sX11MaxDisplays, o->x11_max_displays);
dump_cfg_int(sMaxAuthTries, o->max_authtries);
dump_cfg_int(sMaxSessions, o->max_sessions);
dump_cfg_int(sClientAliveInterval, o->client_alive_interval);
diff -up openssh-7.4p1/servconf.h.x11max openssh-7.4p1/servconf.h
--- openssh-7.4p1/servconf.h.x11max 2017-02-09 12:49:04.741996552 +0100
+++ openssh-7.4p1/servconf.h 2017-02-09 12:49:04.744996547 +0100
@@ -55,6 +55,7 @@
#define DEFAULT_AUTH_FAIL_MAX 6 /* Default for MaxAuthTries */
#define DEFAULT_SESSIONS_MAX 10 /* Default for MaxSessions */
+#define DEFAULT_MAX_DISPLAYS 1000 /* Maximum number of fake X11 displays to try. */
/* Magic name for internal sftp-server */
#define INTERNAL_SFTP_NAME "internal-sftp"
@@ -85,6 +86,7 @@ typedef struct {
int x11_forwarding; /* If true, permit inet (spoofing) X11 fwd. */
int x11_display_offset; /* What DISPLAY number to start
* searching at */
+ int x11_max_displays; /* Number of displays to search */
int x11_use_localhost; /* If true, use localhost for fake X11 server. */
char *xauth_location; /* Location of xauth program */
int permit_tty; /* If false, deny pty allocation */
diff -up openssh-7.4p1/session.c.x11max openssh-7.4p1/session.c
--- openssh-7.4p1/session.c.x11max 2017-02-09 12:49:04.742996550 +0100
+++ openssh-7.4p1/session.c 2017-02-09 12:49:04.745996546 +0100
@@ -2502,8 +2502,9 @@ session_setup_x11fwd(Session *s)
return 0;
}
if (x11_create_display_inet(options.x11_display_offset,
- options.x11_use_localhost, s->single_connection,
- &s->display_number, &s->x11_chanids) == -1) {
+ options.x11_use_localhost, options.x11_max_displays,
+ s->single_connection, &s->display_number,
+ &s->x11_chanids) == -1) {
debug("x11_create_display_inet failed.");
return 0;
}
diff -up openssh-7.4p1/sshd_config.5.x11max openssh-7.4p1/sshd_config.5
--- openssh-7.4p1/sshd_config.5.x11max 2017-02-09 12:49:04.742996550 +0100
+++ openssh-7.4p1/sshd_config.5 2017-02-09 12:51:24.656790909 +0100
@@ -1137,6 +1137,7 @@ Available keywords are
.Cm StreamLocalBindUnlink ,
.Cm TrustedUserCAKeys ,
.Cm X11DisplayOffset ,
+.Cm X11MaxDisplays ,
.Cm X11Forwarding
and
.Cm X11UseLocalHost .
@@ -1563,6 +1564,12 @@ Specifies the first display number avail
X11 forwarding.
This prevents sshd from interfering with real X11 servers.
The default is 10.
+.It Cm X11MaxDisplays
+Specifies the maximum number of displays available for
+.Xr sshd 8 Ns 's
+X11 forwarding.
+This prevents sshd from exhausting local ports.
+The default is 1000.
.It Cm X11Forwarding
Specifies whether X11 forwarding is permitted.
The argument must be