New SSH bug flag, for 'can't handle SSH2_MSG_IGNORE'. Another user
[u/mdw/putty] / ssh.c
diff --git a/ssh.c b/ssh.c
index d30626d..029c78a 100644 (file)
--- a/ssh.c
+++ b/ssh.c
@@ -12,7 +12,9 @@
 #include "putty.h"
 #include "tree234.h"
 #include "ssh.h"
+#ifndef NO_GSSAPI
 #include "sshgss.h"
+#endif
 
 #ifndef FALSE
 #define FALSE 0
@@ -192,6 +194,7 @@ static const char *const ssh2_disconnect_reasons[] = {
 #define BUG_SSH2_REKEY                           64
 #define BUG_SSH2_PK_SESSIONID                   128
 #define BUG_SSH2_MAXPKT                                256
+#define BUG_CHOKES_ON_SSH2_IGNORE               512
 
 /*
  * Codes for terminal modes.
@@ -492,6 +495,16 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
  *
  *  - OUR_V2_BIGWIN is the window size we advertise for the only
  *    channel in a simple connection.  It must be <= INT_MAX.
+ *
+ *  - OUR_V2_MAXPKT is the official "maximum packet size" we send
+ *    to the remote side. This actually has nothing to do with the
+ *    size of the _packet_, but is instead a limit on the amount
+ *    of data we're willing to receive in a single SSH2 channel
+ *    data message.
+ *
+ *  - OUR_V2_PACKETLIMIT is actually the maximum size of SSH
+ *    _packet_ we're prepared to cope with.  It must be a multiple
+ *    of the cipher block size, and must be at least 35000.
  */
 
 #define SSH1_BUFFER_LIMIT 32768
@@ -499,6 +512,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
 #define OUR_V2_WINSIZE 16384
 #define OUR_V2_BIGWIN 0x7fffffff
 #define OUR_V2_MAXPKT 0x4000UL
+#define OUR_V2_PACKETLIMIT 0x9000UL
 
 /* Maximum length of passwords/passphrases (arbitrary) */
 #define SSH_MAX_PASSWORD_LEN 100
@@ -1309,90 +1323,162 @@ static struct Packet *ssh2_rdpkt(Ssh ssh, unsigned char **data, int *datalen)
        st->cipherblk = 8;
     if (st->cipherblk < 8)
        st->cipherblk = 8;
+    st->maclen = ssh->scmac ? ssh->scmac->len : 0;
 
-    st->pktin->data = snewn(st->cipherblk + APIEXTRA, unsigned char);
+    if (ssh->sccipher && (ssh->sccipher->flags & SSH_CIPHER_IS_CBC) &&
+       ssh->scmac) {
+       /*
+        * When dealing with a CBC-mode cipher, we want to avoid the
+        * possibility of an attacker's tweaking the ciphertext stream
+        * so as to cause us to feed the same block to the block
+        * cipher more than once and thus leak information
+        * (VU#958563).  The way we do this is not to take any
+        * decisions on the basis of anything we've decrypted until
+        * we've verified it with a MAC.  That includes the packet
+        * length, so we just read data and check the MAC repeatedly,
+        * and when the MAC passes, see if the length we've got is
+        * plausible.
+        */
 
-    /*
-     * Acquire and decrypt the first block of the packet. This will
-     * contain the length and padding details.
-     */
-    for (st->i = st->len = 0; st->i < st->cipherblk; st->i++) {
-       while ((*datalen) == 0)
-           crReturn(NULL);
-       st->pktin->data[st->i] = *(*data)++;
-       (*datalen)--;
-    }
+       /* May as well allocate the whole lot now. */
+       st->pktin->data = snewn(OUR_V2_PACKETLIMIT + st->maclen + APIEXTRA,
+                               unsigned char);
 
-    if (ssh->sccipher)
-       ssh->sccipher->decrypt(ssh->sc_cipher_ctx,
-                              st->pktin->data, st->cipherblk);
+       /* Read an amount corresponding to the MAC. */
+       for (st->i = 0; st->i < st->maclen; st->i++) {
+           while ((*datalen) == 0)
+               crReturn(NULL);
+           st->pktin->data[st->i] = *(*data)++;
+           (*datalen)--;
+       }
 
-    /*
-     * Now get the length and padding figures.
-     */
-    st->len = GET_32BIT(st->pktin->data);
-    st->pad = st->pktin->data[4];
+       st->packetlen = 0;
+       {
+           unsigned char seq[4];
+           ssh->scmac->start(ssh->sc_mac_ctx);
+           PUT_32BIT(seq, st->incoming_sequence);
+           ssh->scmac->bytes(ssh->sc_mac_ctx, seq, 4);
+       }
 
-    /*
-     * _Completely_ silly lengths should be stomped on before they
-     * do us any more damage.
-     */
-    if (st->len < 0 || st->len > 35000 || st->pad < 4 ||
-       st->len - st->pad < 1 || (st->len + 4) % st->cipherblk != 0) {
-       bombout(("Incoming packet was garbled on decryption"));
-       ssh_free_packet(st->pktin);
-       crStop(NULL);
-    }
+       for (;;) { /* Once around this loop per cipher block. */
+           /* Read another cipher-block's worth, and tack it onto the end. */
+           for (st->i = 0; st->i < st->cipherblk; st->i++) {
+               while ((*datalen) == 0)
+                   crReturn(NULL);
+               st->pktin->data[st->packetlen+st->maclen+st->i] = *(*data)++;
+               (*datalen)--;
+           }
+           /* Decrypt one more block (a little further back in the stream). */
+           ssh->sccipher->decrypt(ssh->sc_cipher_ctx,
+                                  st->pktin->data + st->packetlen,
+                                  st->cipherblk);
+           /* Feed that block to the MAC. */
+           ssh->scmac->bytes(ssh->sc_mac_ctx,
+                             st->pktin->data + st->packetlen, st->cipherblk);
+           st->packetlen += st->cipherblk;
+           /* See if that gives us a valid packet. */
+           if (ssh->scmac->verresult(ssh->sc_mac_ctx,
+                                     st->pktin->data + st->packetlen) &&
+               (st->len = GET_32BIT(st->pktin->data)) + 4 == st->packetlen)
+                   break;
+           if (st->packetlen >= OUR_V2_PACKETLIMIT) {
+               bombout(("No valid incoming packet found"));
+               ssh_free_packet(st->pktin);
+               crStop(NULL);
+           }       
+       }
+       st->pktin->maxlen = st->packetlen + st->maclen;
+       st->pktin->data = sresize(st->pktin->data,
+                                 st->pktin->maxlen + APIEXTRA,
+                                 unsigned char);
+    } else {
+       st->pktin->data = snewn(st->cipherblk + APIEXTRA, unsigned char);
 
-    /*
-     * This enables us to deduce the payload length.
-     */
-    st->payload = st->len - st->pad - 1;
+       /*
+        * Acquire and decrypt the first block of the packet. This will
+        * contain the length and padding details.
+        */
+       for (st->i = st->len = 0; st->i < st->cipherblk; st->i++) {
+           while ((*datalen) == 0)
+               crReturn(NULL);
+           st->pktin->data[st->i] = *(*data)++;
+           (*datalen)--;
+       }
 
-    st->pktin->length = st->payload + 5;
+       if (ssh->sccipher)
+           ssh->sccipher->decrypt(ssh->sc_cipher_ctx,
+                                  st->pktin->data, st->cipherblk);
 
-    /*
-     * So now we can work out the total packet length.
-     */
-    st->packetlen = st->len + 4;
-    st->maclen = ssh->scmac ? ssh->scmac->len : 0;
+       /*
+        * Now get the length figure.
+        */
+       st->len = GET_32BIT(st->pktin->data);
 
-    /*
-     * Allocate memory for the rest of the packet.
-     */
-    st->pktin->maxlen = st->packetlen + st->maclen;
-    st->pktin->data = sresize(st->pktin->data,
-                             st->pktin->maxlen + APIEXTRA,
-                             unsigned char);
+       /*
+        * _Completely_ silly lengths should be stomped on before they
+        * do us any more damage.
+        */
+       if (st->len < 0 || st->len > OUR_V2_PACKETLIMIT ||
+           (st->len + 4) % st->cipherblk != 0) {
+           bombout(("Incoming packet was garbled on decryption"));
+           ssh_free_packet(st->pktin);
+           crStop(NULL);
+       }
 
-    /*
-     * Read and decrypt the remainder of the packet.
-     */
-    for (st->i = st->cipherblk; st->i < st->packetlen + st->maclen;
-        st->i++) {
-       while ((*datalen) == 0)
-           crReturn(NULL);
-       st->pktin->data[st->i] = *(*data)++;
-       (*datalen)--;
-    }
-    /* Decrypt everything _except_ the MAC. */
-    if (ssh->sccipher)
-       ssh->sccipher->decrypt(ssh->sc_cipher_ctx,
-                              st->pktin->data + st->cipherblk,
-                              st->packetlen - st->cipherblk);
+       /*
+        * So now we can work out the total packet length.
+        */
+       st->packetlen = st->len + 4;
 
-    st->pktin->encrypted_len = st->packetlen;
+       /*
+        * Allocate memory for the rest of the packet.
+        */
+       st->pktin->maxlen = st->packetlen + st->maclen;
+       st->pktin->data = sresize(st->pktin->data,
+                                 st->pktin->maxlen + APIEXTRA,
+                                 unsigned char);
 
-    /*
-     * Check the MAC.
-     */
-    if (ssh->scmac
-       && !ssh->scmac->verify(ssh->sc_mac_ctx, st->pktin->data, st->len + 4,
-                              st->incoming_sequence)) {
-       bombout(("Incorrect MAC received on packet"));
+       /*
+        * Read and decrypt the remainder of the packet.
+        */
+       for (st->i = st->cipherblk; st->i < st->packetlen + st->maclen;
+            st->i++) {
+           while ((*datalen) == 0)
+               crReturn(NULL);
+           st->pktin->data[st->i] = *(*data)++;
+           (*datalen)--;
+       }
+       /* Decrypt everything _except_ the MAC. */
+       if (ssh->sccipher)
+           ssh->sccipher->decrypt(ssh->sc_cipher_ctx,
+                                  st->pktin->data + st->cipherblk,
+                                  st->packetlen - st->cipherblk);
+
+       /*
+        * Check the MAC.
+        */
+       if (ssh->scmac
+           && !ssh->scmac->verify(ssh->sc_mac_ctx, st->pktin->data,
+                                  st->len + 4, st->incoming_sequence)) {
+           bombout(("Incorrect MAC received on packet"));
+           ssh_free_packet(st->pktin);
+           crStop(NULL);
+       }
+    }
+    /* Get and sanity-check the amount of random padding. */
+    st->pad = st->pktin->data[4];
+    if (st->pad < 4 || st->len - st->pad < 1) {
+       bombout(("Invalid padding length on received packet"));
        ssh_free_packet(st->pktin);
        crStop(NULL);
     }
+    /*
+     * This enables us to deduce the payload length.
+     */
+    st->payload = st->len - st->pad - 1;
+
+    st->pktin->length = st->payload + 5;
+    st->pktin->encrypted_len = st->packetlen;
 
     st->pktin->sequence = st->incoming_sequence++;
 
@@ -1926,7 +2012,8 @@ static void ssh2_pkt_defer_noqueue(Ssh ssh, struct Packet *pkt, int noignore)
 {
     int len;
     if (ssh->cscipher != NULL && (ssh->cscipher->flags & SSH_CIPHER_IS_CBC) &&
-       ssh->deferred_len == 0 && !noignore) {
+       ssh->deferred_len == 0 && !noignore &&
+       !(ssh->remote_bugs & BUG_CHOKES_ON_SSH2_IGNORE)) {
        /*
         * Interpose an SSH_MSG_IGNORE to ensure that user data don't
         * get encrypted with a known IV.
@@ -2056,7 +2143,8 @@ static void ssh2_pkt_send_with_padding(Ssh ssh, struct Packet *pkt,
         * unavailable, we don't do this trick at all, because we
         * gain nothing by it.)
         */
-       if (ssh->cscipher) {
+       if (ssh->cscipher &&
+           !(ssh->remote_bugs & BUG_CHOKES_ON_SSH2_IGNORE)) {
            int stringlen, i;
 
            stringlen = (256 - ssh->deferred_len);
@@ -2423,6 +2511,15 @@ static void ssh_detect_bugs(Ssh ssh, char *vstring)
        ssh->remote_bugs |= BUG_SSH2_MAXPKT;
        logevent("We believe remote version ignores SSH-2 maximum packet size");
     }
+
+    if (ssh->cfg.sshbug_ignore2 == FORCE_ON) {
+       /*
+        * Servers that don't support SSH2_MSG_IGNORE. Currently,
+        * none detected automatically.
+        */
+       ssh->remote_bugs |= BUG_CHOKES_ON_SSH2_IGNORE;
+       logevent("We believe remote version has SSH-2 ignore bug");
+    }
 }
 
 /*
@@ -2768,6 +2865,8 @@ static int ssh_do_close(Ssh ssh, int notify_exit)
            del234(ssh->portfwds, pf); /* moving next one to index 0 */
            free_portfwd(pf);
        }
+       freetree234(ssh->portfwds);
+       ssh->portfwds = NULL;
     }
 
     return ret;
@@ -3361,7 +3460,8 @@ static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen,
 
     fflush(stdout); /* FIXME eh? */
     {
-       if (!*ssh->cfg.username) {
+       if (!get_remote_username(&ssh->cfg, s->username,
+                                sizeof(s->username))) {
            int ret; /* need not be kept over crReturn */
            s->cur_prompt = new_prompts(ssh->frontend);
            s->cur_prompt->to_server = TRUE;
@@ -3386,9 +3486,6 @@ static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen,
            memcpy(s->username, s->cur_prompt->prompts[0]->result,
                   lenof(s->username));
            free_prompts(s->cur_prompt);
-       } else {
-           strncpy(s->username, ssh->cfg.username, sizeof(s->username));
-           s->username[sizeof(s->username)-1] = '\0';
        }
 
        send_packet(ssh, SSH1_CMSG_USER, PKT_STR, s->username, PKT_END);
@@ -4344,12 +4441,19 @@ static void ssh_setup_portfwd(Ssh ssh, const Config *cfg)
 
            epfrec = add234(ssh->portfwds, pfrec);
            if (epfrec != pfrec) {
+               if (epfrec->status == DESTROY) {
+                   /*
+                    * We already have a port forwarding up and running
+                    * with precisely these parameters. Hence, no need
+                    * to do anything; simply re-tag the existing one
+                    * as KEEP.
+                    */
+                   epfrec->status = KEEP;
+               }
                /*
-                * We already have a port forwarding with precisely
-                * these parameters. Hence, no need to do anything;
-                * simply tag the existing one as KEEP.
+                * Anything else indicates that there was a duplicate
+                * in our input, which we'll silently ignore.
                 */
-               epfrec->status = KEEP;
                free_portfwd(pfrec);
            } else {
                pfrec->status = CREATE;
@@ -4913,10 +5017,10 @@ static void do_ssh1_connection(Ssh ssh, unsigned char *in, int inlen,
        }
     }
 
-    if (ssh->cfg.x11_forward) {
+    if (ssh->cfg.x11_forward &&
+       (ssh->x11disp = x11_setup_display(ssh->cfg.x11_display,
+                                         ssh->cfg.x11_auth, &ssh->cfg))) {
        logevent("Requesting X11 forwarding");
-       ssh->x11disp = x11_setup_display(ssh->cfg.x11_display,
-                                        ssh->cfg.x11_auth, &ssh->cfg);
        /*
         * Note that while we blank the X authentication data here, we don't
         * take any special action to blank the start of an X11 channel,
@@ -6578,11 +6682,13 @@ static void ssh2_msg_channel_eof(Ssh ssh, struct Packet *pktin)
         * wrap up and close the channel ourselves.
         */
        x11_close(c->u.x11.s);
+       c->u.x11.s = NULL;
        sshfwd_close(c);
     } else if (c->type == CHAN_AGENT) {
        sshfwd_close(c);
     } else if (c->type == CHAN_SOCKDATA) {
        pfd_close(c->u.pfd.s);
+       c->u.pfd.s = NULL;
        sshfwd_close(c);
     }
 }
@@ -6930,6 +7036,7 @@ static void ssh2_msg_channel_open(Ssh ssh, struct Packet *pktin)
 
     if (typelen == 3 && !memcmp(type, "x11", 3)) {
        char *addrstr;
+       const char *x11err;
 
        ssh_pkt_getstring(pktin, &peeraddr, &peeraddrlen);
        addrstr = snewn(peeraddrlen+1, char);
@@ -6942,8 +7049,9 @@ static void ssh2_msg_channel_open(Ssh ssh, struct Packet *pktin)
 
        if (!ssh->X11_fwd_enabled)
            error = "X11 forwarding is not enabled";
-       else if (x11_init(&c->u.x11.s, ssh->x11disp, c,
-                         addrstr, peerport, &ssh->cfg) != NULL) {
+       else if ((x11err = x11_init(&c->u.x11.s, ssh->x11disp, c,
+                                   addrstr, peerport, &ssh->cfg)) != NULL) {
+           logeventf(ssh, "Local X11 connection failed: %s", x11err);
            error = "Unable to open an X11 connection";
        } else {
            logevent("Opening X11 forward connection succeeded");
@@ -7073,8 +7181,10 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
        int done_service_req;
        int gotit, need_pw, can_pubkey, can_passwd, can_keyb_inter;
        int tried_pubkey_config, done_agent;
+#ifndef NO_GSSAPI
        int can_gssapi;
        int tried_gssapi;
+#endif
        int kbd_inter_refused;
        int we_are_in;
        prompts_t *cur_prompt;
@@ -7098,11 +7208,13 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
        int try_send;
        int num_env, env_left, env_ok;
        struct Packet *pktout;
+#ifndef NO_GSSAPI
        Ssh_gss_ctx gss_ctx;
        Ssh_gss_buf gss_buf;
        Ssh_gss_buf gss_rcvtok, gss_sndtok;
        Ssh_gss_name gss_srv_name;
        Ssh_gss_stat gss_stat;
+#endif
     };
     crState(do_ssh2_authconn_state);
 
@@ -7110,7 +7222,9 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
 
     s->done_service_req = FALSE;
     s->we_are_in = FALSE;
+#ifndef NO_GSSAPI
     s->tried_gssapi = FALSE;
+#endif
 
     if (!ssh->cfg.ssh_no_userauth) {
        /*
@@ -7295,7 +7409,8 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
             * with change_username turned off we don't try to get
             * it again.
             */
-       } else if (!*ssh->cfg.username) {
+       } else if (!get_remote_username(&ssh->cfg, s->username,
+                                       sizeof(s->username))) {
            int ret; /* need not be kept over crReturn */
            s->cur_prompt = new_prompts(ssh->frontend);
            s->cur_prompt->to_server = TRUE;
@@ -7323,8 +7438,6 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
            free_prompts(s->cur_prompt);
        } else {
            char *stuff;
-           strncpy(s->username, ssh->cfg.username, sizeof(s->username));
-           s->username[sizeof(s->username)-1] = '\0';
            if ((flags & FLAG_VERBOSE) || (flags & FLAG_INTERACTIVE)) {
                stuff = dupprintf("Using username \"%s\".\r\n", s->username);
                c_write_str(ssh, stuff);
@@ -7808,7 +7921,8 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
 
                /* GSSAPI Authentication */
 
-               int micoffset;
+               int micoffset, len;
+               char *data;
                Ssh_gss_buf mic;
                s->type = AUTH_TYPE_GSSAPI;
                s->tried_gssapi = TRUE;
@@ -7828,13 +7942,14 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
                ssh2_pkt_adduint32(s->pktout,1);
 
                /* length of OID + 2 */
-               ssh2_pkt_adduint32(s->pktout, s->gss_buf.len + 2);
+               ssh2_pkt_adduint32(s->pktout, s->gss_buf.length + 2);
                ssh2_pkt_addbyte(s->pktout, SSH2_GSS_OIDTYPE);
 
                /* length of OID */
-               ssh2_pkt_addbyte(s->pktout, (unsigned char) s->gss_buf.len);
+               ssh2_pkt_addbyte(s->pktout, (unsigned char) s->gss_buf.length);
 
-               ssh_pkt_adddata(s->pktout, s->gss_buf.data, s->gss_buf.len);
+               ssh_pkt_adddata(s->pktout, s->gss_buf.value,
+                               s->gss_buf.length);
                ssh2_pkt_send(ssh, s->pktout);
                crWaitUntilV(pktin);
                if (pktin->type != SSH2_MSG_USERAUTH_GSSAPI_RESPONSE) {
@@ -7844,11 +7959,14 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
 
                /* check returned packet ... */
 
-               ssh_pkt_getstring(pktin,&s->gss_rcvtok.data,&s->gss_rcvtok.len);
-               if (s->gss_rcvtok.len != s->gss_buf.len + 2 ||
-                   s->gss_rcvtok.data[0] != SSH2_GSS_OIDTYPE ||
-                   s->gss_rcvtok.data[1] != s->gss_buf.len ||
-                   memcmp(s->gss_rcvtok.data+2,s->gss_buf.data,s->gss_buf.len) ) {
+               ssh_pkt_getstring(pktin, &data, &len);
+               s->gss_rcvtok.value = data;
+               s->gss_rcvtok.length = len;
+               if (s->gss_rcvtok.length != s->gss_buf.length + 2 ||
+                   ((char *)s->gss_rcvtok.value)[0] != SSH2_GSS_OIDTYPE ||
+                   ((char *)s->gss_rcvtok.value)[1] != s->gss_buf.length ||
+                   memcmp((char *)s->gss_rcvtok.value + 2,
+                          s->gss_buf.value,s->gss_buf.length) ) {
                    logevent("GSSAPI authentication - wrong response from server");
                    continue;
                }
@@ -7874,8 +7992,8 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
                }
 
                /* initial tokens are empty */
-               s->gss_rcvtok.len = s->gss_sndtok.len = 0;
-               s->gss_rcvtok.data = s->gss_sndtok.data = NULL;
+               SSH_GSS_CLEAR_BUF(&s->gss_rcvtok);
+               SSH_GSS_CLEAR_BUF(&s->gss_sndtok);
 
                /* now enter the loop */
                do {
@@ -7890,8 +8008,8 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
                        logevent("GSSAPI authentication initialisation failed");
 
                        if (ssh_gss_display_status(s->gss_ctx,&s->gss_buf) == SSH_GSS_OK) {
-                           logevent(s->gss_buf.data);
-                           sfree(s->gss_buf.data);
+                           logevent(s->gss_buf.value);
+                           sfree(s->gss_buf.value);
                        }
 
                        break;
@@ -7901,10 +8019,10 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
                    /* Client and server now exchange tokens until GSSAPI
                     * no longer says CONTINUE_NEEDED */
 
-                   if (s->gss_sndtok.len != 0) {
+                   if (s->gss_sndtok.length != 0) {
                        s->pktout = ssh2_pkt_init(SSH2_MSG_USERAUTH_GSSAPI_TOKEN);
                        ssh_pkt_addstring_start(s->pktout);
-                       ssh_pkt_addstring_data(s->pktout,s->gss_sndtok.data,s->gss_sndtok.len);
+                       ssh_pkt_addstring_data(s->pktout,s->gss_sndtok.value,s->gss_sndtok.length);
                        ssh2_pkt_send(ssh, s->pktout);
                        ssh_gss_free_tok(&s->gss_sndtok);
                    }
@@ -7916,7 +8034,9 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
                            s->gss_stat = SSH_GSS_FAILURE;
                            break;
                        }
-                       ssh_pkt_getstring(pktin,&s->gss_rcvtok.data,&s->gss_rcvtok.len);
+                       ssh_pkt_getstring(pktin, &data, &len);
+                       s->gss_rcvtok.value = data;
+                       s->gss_rcvtok.length = len;
                    }
                } while (s-> gss_stat == SSH_GSS_S_CONTINUE_NEEDED);
 
@@ -7938,13 +8058,13 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
                ssh_pkt_addstring(s->pktout, "ssh-connection");
                ssh_pkt_addstring(s->pktout, "gssapi-with-mic");
 
-               s->gss_buf.data = (char *)s->pktout->data + micoffset;
-               s->gss_buf.len = s->pktout->length - micoffset;
+               s->gss_buf.value = (char *)s->pktout->data + micoffset;
+               s->gss_buf.length = s->pktout->length - micoffset;
 
                ssh_gss_get_mic(s->gss_ctx, &s->gss_buf, &mic);
                s->pktout = ssh2_pkt_init(SSH2_MSG_USERAUTH_GSSAPI_MIC);
                ssh_pkt_addstring_start(s->pktout);
-               ssh_pkt_addstring_data(s->pktout, mic.data, mic.len);
+               ssh_pkt_addstring_data(s->pktout, mic.value, mic.length);
                ssh2_pkt_send(ssh, s->pktout);
                ssh_gss_free_mic(&mic);
 
@@ -8006,23 +8126,6 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
                    ssh_pkt_getstring(pktin, &lang, &lang_len);
                    s->cur_prompt = new_prompts(ssh->frontend);
                    s->cur_prompt->to_server = TRUE;
-                   if (name_len) {
-                       /* FIXME: better prefix to distinguish from
-                        * local prompts? */
-                       s->cur_prompt->name =
-                           dupprintf("SSH server: %.*s", name_len, name);
-                       s->cur_prompt->name_reqd = TRUE;
-                   } else {
-                       s->cur_prompt->name =
-                           dupstr("SSH server authentication");
-                       s->cur_prompt->name_reqd = FALSE;
-                   }
-                   /* FIXME: ugly to print "Using..." in prompt _every_
-                    * time round. Can this be done more subtly? */
-                   s->cur_prompt->instruction =
-                       dupprintf("Using keyboard-interactive authentication.%s%.*s",
-                                 inst_len ? "\n" : "", inst_len, inst);
-                   s->cur_prompt->instr_reqd = TRUE;
 
                    /*
                     * Get any prompt(s) from the packet.
@@ -8046,6 +8149,33 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
                                   echo, SSH_MAX_PASSWORD_LEN);
                    }
 
+                   if (name_len) {
+                       /* FIXME: better prefix to distinguish from
+                        * local prompts? */
+                       s->cur_prompt->name =
+                           dupprintf("SSH server: %.*s", name_len, name);
+                       s->cur_prompt->name_reqd = TRUE;
+                   } else {
+                       s->cur_prompt->name =
+                           dupstr("SSH server authentication");
+                       s->cur_prompt->name_reqd = FALSE;
+                   }
+                   /* We add a prefix to try to make it clear that a prompt
+                    * has come from the server.
+                    * FIXME: ugly to print "Using..." in prompt _every_
+                    * time round. Can this be done more subtly? */
+                   /* Special case: for reasons best known to themselves,
+                    * some servers send k-i requests with no prompts and
+                    * nothing to display. Keep quiet in this case. */
+                   if (s->num_prompts || name_len || inst_len) {
+                       s->cur_prompt->instruction =
+                           dupprintf("Using keyboard-interactive authentication.%s%.*s",
+                                     inst_len ? "\n" : "", inst_len, inst);
+                       s->cur_prompt->instr_reqd = TRUE;
+                   } else {
+                       s->cur_prompt->instr_reqd = FALSE;
+                   }
+
                    /*
                      * Display any instructions, and get the user's
                      * response(s).
@@ -8463,7 +8593,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
     ssh->packet_dispatch[SSH2_MSG_CHANNEL_OPEN] =
        ssh2_msg_channel_open;
 
-    if (ssh->cfg.ssh_simple) {
+    if (ssh->mainchan && ssh->cfg.ssh_simple) {
        /*
         * This message indicates to the server that we promise
         * not to try to run any other channel in parallel with
@@ -8480,10 +8610,10 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
     /*
      * Potentially enable X11 forwarding.
      */
-    if (ssh->mainchan && !ssh->ncmode && ssh->cfg.x11_forward) {
+    if (ssh->mainchan && !ssh->ncmode && ssh->cfg.x11_forward &&
+       (ssh->x11disp = x11_setup_display(ssh->cfg.x11_display,
+                                         ssh->cfg.x11_auth, &ssh->cfg))) {
        logevent("Requesting X11 forwarding");
-       ssh->x11disp = x11_setup_display(ssh->cfg.x11_display,
-                                        ssh->cfg.x11_auth, &ssh->cfg);
        s->pktout = ssh2_pkt_init(SSH2_MSG_CHANNEL_REQUEST);
        ssh2_pkt_adduint32(s->pktout, ssh->mainchan->remoteid);
        ssh2_pkt_addstring(s->pktout, "x11-req");
@@ -9308,8 +9438,10 @@ static const struct telnet_special *ssh_get_specials(void *handle)
     static const struct telnet_special ssh1_ignore_special[] = {
        {"IGNORE message", TS_NOP}
     };
-    static const struct telnet_special ssh2_transport_specials[] = {
+    static const struct telnet_special ssh2_ignore_special[] = {
        {"IGNORE message", TS_NOP},
+    };
+    static const struct telnet_special ssh2_rekey_special[] = {
        {"Repeat key exchange", TS_REKEY},
     };
     static const struct telnet_special ssh2_session_specials[] = {
@@ -9334,7 +9466,8 @@ static const struct telnet_special *ssh_get_specials(void *handle)
        {NULL, TS_EXITMENU}
     };
     /* XXX review this length for any changes: */
-    static struct telnet_special ssh_specials[lenof(ssh2_transport_specials) +
+    static struct telnet_special ssh_specials[lenof(ssh2_ignore_special) +
+                                             lenof(ssh2_rekey_special) +
                                              lenof(ssh2_session_specials) +
                                              lenof(specials_end)];
     Ssh ssh = (Ssh) handle;
@@ -9353,7 +9486,10 @@ static const struct telnet_special *ssh_get_specials(void *handle)
        if (!(ssh->remote_bugs & BUG_CHOKES_ON_SSH1_IGNORE))
            ADD_SPECIALS(ssh1_ignore_special);
     } else if (ssh->version == 2) {
-       ADD_SPECIALS(ssh2_transport_specials);
+       if (!(ssh->remote_bugs & BUG_CHOKES_ON_SSH2_IGNORE))
+           ADD_SPECIALS(ssh2_ignore_special);
+       if (!(ssh->remote_bugs & BUG_SSH2_REKEY))
+           ADD_SPECIALS(ssh2_rekey_special);
        if (ssh->mainchan)
            ADD_SPECIALS(ssh2_session_specials);
     } /* else we're not ready yet */
@@ -9403,9 +9539,11 @@ static void ssh_special(void *handle, Telnet_Special code)
            if (!(ssh->remote_bugs & BUG_CHOKES_ON_SSH1_IGNORE))
                send_packet(ssh, SSH1_MSG_IGNORE, PKT_STR, "", PKT_END);
        } else {
-           pktout = ssh2_pkt_init(SSH2_MSG_IGNORE);
-           ssh2_pkt_addstring_start(pktout);
-           ssh2_pkt_send_noqueue(ssh, pktout);
+           if (!(ssh->remote_bugs & BUG_CHOKES_ON_SSH2_IGNORE)) {
+               pktout = ssh2_pkt_init(SSH2_MSG_IGNORE);
+               ssh2_pkt_addstring_start(pktout);
+               ssh2_pkt_send_noqueue(ssh, pktout);
+           }
        }
     } else if (code == TS_REKEY) {
        if (!ssh->kex_in_progress && ssh->version == 2) {