Implement part of `ssh2-generality': introduce the ability to tell
[u/mdw/putty] / ssh.c
diff --git a/ssh.c b/ssh.c
index 60b0301..8356a07 100644 (file)
--- a/ssh.c
+++ b/ssh.c
@@ -267,7 +267,13 @@ static char *ssh2_pkt_type(int pkt_ctx, int type)
     (cp)[2] = (unsigned char)((value) >> 8); \
     (cp)[3] = (unsigned char)(value); }
 
-enum { PKT_END, PKT_INT, PKT_CHAR, PKT_DATA, PKT_STR, PKT_BIGNUM };
+/* Enumeration values for fields in SSH-1 packets */
+enum {
+    PKT_END, PKT_INT, PKT_CHAR, PKT_DATA, PKT_STR, PKT_BIGNUM,
+    /* These values are for communicating relevant semantics of
+     * fields to the packet logging code. */
+    PKTT_OTHER, PKTT_PASSWORD, PKTT_DATA
+};
 
 /*
  * Coroutine mechanics for the sillier bits of the code. If these
@@ -598,6 +604,13 @@ struct ssh_tag {
     int deferred_len, deferred_size;
 
     /*
+     * State associated with packet logging
+     */
+    int pktout_logmode;
+    int pktout_nblanks;
+    struct logblank_t *pktout_blanks;
+
+    /*
      * Gross hack: pscp will try to start SFTP but fall back to
      * scp1 if that fails. This variable is the means by which
      * scp.c can reach into the SSH code and find out which one it
@@ -684,6 +697,25 @@ static void logeventf(Ssh ssh, const char *fmt, ...)
         sfree(text); \
     } while (0)
 
+/* Functions to leave bits out of the SSH packet log file. */
+
+static void dont_log_password(Ssh ssh, int blanktype)
+{
+    if (ssh->cfg.logomitpass)
+       ssh->pktout_logmode = blanktype;
+}
+
+static void dont_log_data(Ssh ssh, int blanktype)
+{
+    if (ssh->cfg.logomitdata)
+       ssh->pktout_logmode = blanktype;
+}
+
+static void end_log_omission(Ssh ssh)
+{
+    ssh->pktout_logmode = PKTLOG_EMIT;
+}
+
 static int ssh_channelcmp(void *av, void *bv)
 {
     struct ssh_channel *a = (struct ssh_channel *) av;
@@ -898,11 +930,34 @@ static int ssh1_rdpkt(Ssh ssh, unsigned char **data, int *datalen)
 
     ssh->pktin.type = ssh->pktin.body[-1];
 
-    if (ssh->logctx)
+    /*
+     * Log incoming packet, possibly omitting sensitive fields.
+     */
+    if (ssh->logctx) {
+       int nblanks = 0;
+       struct logblank_t blank;
+       if (ssh->cfg.logomitdata) {
+           int do_blank = FALSE, blank_prefix = 0;
+           /* "Session data" packets - omit the data field */
+           if ((ssh->pktin.type == SSH1_SMSG_STDOUT_DATA) ||
+               (ssh->pktin.type == SSH1_SMSG_STDERR_DATA)) {
+               do_blank = TRUE; blank_prefix = 0;
+           } else if (ssh->pktin.type == SSH1_MSG_CHANNEL_DATA) {
+               do_blank = TRUE; blank_prefix = 4;
+           }
+           if (do_blank) {
+               blank.offset = blank_prefix;
+               blank.len = ssh->pktin.length;
+               blank.type = PKTLOG_OMIT;
+               nblanks = 1;
+           }
+       }
        log_packet(ssh->logctx,
                   PKT_INCOMING, ssh->pktin.type,
                   ssh1_pkt_type(ssh->pktin.type),
-                  ssh->pktin.body, ssh->pktin.length);
+                  ssh->pktin.body, ssh->pktin.length,
+                  nblanks, &blank);
+    }
 
     if (ssh->pktin.type == SSH1_SMSG_STDOUT_DATA ||
        ssh->pktin.type == SSH1_SMSG_STDERR_DATA ||
@@ -1079,10 +1134,32 @@ static int ssh2_rdpkt(Ssh ssh, unsigned char **data, int *datalen)
     ssh->pktin.body = ssh->pktin.data;
     ssh->pktin.type = ssh->pktin.data[5];
 
-    if (ssh->logctx)
+    /*
+     * Log incoming packet, possibly omitting sensitive fields.
+     */
+    if (ssh->logctx) {
+       int nblanks = 0;
+       struct logblank_t blank;
+       if (ssh->cfg.logomitdata) {
+           int do_blank = FALSE, blank_prefix = 0;
+           /* "Session data" packets - omit the data field */
+           if (ssh->pktin.type == SSH2_MSG_CHANNEL_DATA) {
+               do_blank = TRUE; blank_prefix = 4;
+           } else if (ssh->pktin.type == SSH2_MSG_CHANNEL_EXTENDED_DATA) {
+               do_blank = TRUE; blank_prefix = 8;
+           }
+           if (do_blank) {
+               blank.offset = blank_prefix;
+               blank.len = (ssh->pktin.length-6) - blank_prefix;
+               blank.type = PKTLOG_OMIT;
+               nblanks = 1;
+           }
+       }
        log_packet(ssh->logctx, PKT_INCOMING, ssh->pktin.type,
                   ssh2_pkt_type(ssh->pkt_ctx, ssh->pktin.type),
-                  ssh->pktin.data+6, ssh->pktin.length-6);
+                  ssh->pktin.data+6, ssh->pktin.length-6,
+                  nblanks, &blank);
+    }
 
     switch (ssh->pktin.type) {
         /*
@@ -1215,6 +1292,9 @@ static void s_wrpkt_start(Ssh ssh, int type, int len)
 {
     ssh1_pktout_size(ssh, len);
     ssh->pktout.type = type;
+    /* Initialise log omission state */
+    ssh->pktout_nblanks = 0;
+    ssh->pktout_blanks = NULL;
 }
 
 static int s_wrpkt_prepare(Ssh ssh)
@@ -1237,7 +1317,10 @@ static int s_wrpkt_prepare(Ssh ssh)
     if (ssh->logctx)
        log_packet(ssh->logctx, PKT_OUTGOING, ssh->pktout.type,
                   ssh1_pkt_type(ssh->pktout.type),
-                  ssh->pktout.body, ssh->pktout.length);
+                  ssh->pktout.body, ssh->pktout.length,
+                  ssh->pktout_nblanks, ssh->pktout_blanks);
+    sfree(ssh->pktout_blanks); ssh->pktout_blanks = NULL;
+    ssh->pktout_nblanks = 0;
 
     if (ssh->v1_compressing) {
        unsigned char *compblk;
@@ -1324,6 +1407,11 @@ static void construct_packet(Ssh ssh, int pkttype, va_list ap1, va_list ap2)
            bn = va_arg(ap1, Bignum);
            pktlen += ssh1_bignum_length(bn);
            break;
+         case PKTT_PASSWORD:
+         case PKTT_DATA:
+         case PKTT_OTHER:
+           /* ignore this pass */
+           break;
          default:
            assert(0);
        }
@@ -1333,34 +1421,58 @@ static void construct_packet(Ssh ssh, int pkttype, va_list ap1, va_list ap2)
     p = ssh->pktout.body;
 
     while ((argtype = va_arg(ap2, int)) != PKT_END) {
+       int offset = p - ssh->pktout.body, len = 0;
        switch (argtype) {
+         /* Actual fields in the packet */
          case PKT_INT:
            argint = va_arg(ap2, int);
            PUT_32BIT(p, argint);
-           p += 4;
+           len = 4;
            break;
          case PKT_CHAR:
            argchar = (unsigned char) va_arg(ap2, int);
            *p = argchar;
-           p++;
+           len = 1;
            break;
          case PKT_DATA:
            argp = va_arg(ap2, unsigned char *);
            arglen = va_arg(ap2, int);
            memcpy(p, argp, arglen);
-           p += arglen;
+           len = arglen;
            break;
          case PKT_STR:
            argp = va_arg(ap2, unsigned char *);
            arglen = strlen((char *)argp);
            PUT_32BIT(p, arglen);
            memcpy(p + 4, argp, arglen);
-           p += 4 + arglen;
+           len = arglen + 4;
            break;
          case PKT_BIGNUM:
            bn = va_arg(ap2, Bignum);
-           p += ssh1_write_bignum(p, bn);
+           len = ssh1_write_bignum(p, bn);
+           break;
+         /* Tokens for modifications to packet logging */
+         case PKTT_PASSWORD:
+           dont_log_password(ssh, PKTLOG_BLANK);
+           break;
+         case PKTT_DATA:
+           dont_log_data(ssh, PKTLOG_OMIT);
            break;
+         case PKTT_OTHER:
+           end_log_omission(ssh);
+           break;
+       }
+       p += len;
+       /* Deal with logfile omission, if required. */
+       if (len && (ssh->pktout_logmode != PKTLOG_EMIT)) {
+           ssh->pktout_nblanks++;
+           ssh->pktout_blanks = sresize(ssh->pktout_blanks,
+                                        ssh->pktout_nblanks,
+                                        struct logblank_t);
+           ssh->pktout_blanks[ssh->pktout_nblanks-1].offset = offset;
+           ssh->pktout_blanks[ssh->pktout_nblanks-1].len    = len;
+           ssh->pktout_blanks[ssh->pktout_nblanks-1].type   =
+               ssh->pktout_logmode;
        }
     }
 }
@@ -1439,6 +1551,15 @@ static void ssh2_pkt_ensure(Ssh ssh, int length)
 }
 static void ssh2_pkt_adddata(Ssh ssh, void *data, int len)
 {
+    if (ssh->pktout_logmode != PKTLOG_EMIT) {
+       ssh->pktout_nblanks++;
+       ssh->pktout_blanks = sresize(ssh->pktout_blanks, ssh->pktout_nblanks,
+                                    struct logblank_t);
+       ssh->pktout_blanks[ssh->pktout_nblanks-1].offset =
+           ssh->pktout.length - 6;
+       ssh->pktout_blanks[ssh->pktout_nblanks-1].len = len;
+       ssh->pktout_blanks[ssh->pktout_nblanks-1].type = ssh->pktout_logmode;
+    }
     ssh->pktout.length += len;
     ssh2_pkt_ensure(ssh, ssh->pktout.length);
     memcpy(ssh->pktout.data + ssh->pktout.length - len, data, len);
@@ -1450,6 +1571,7 @@ static void ssh2_pkt_addbyte(Ssh ssh, unsigned char byte)
 static void ssh2_pkt_init(Ssh ssh, int pkt_type)
 {
     ssh->pktout.length = 5;
+    ssh->pktout_nblanks = 0; ssh->pktout_blanks = NULL;
     ssh2_pkt_addbyte(ssh, (unsigned char) pkt_type);
 }
 static void ssh2_pkt_addbool(Ssh ssh, unsigned char value)
@@ -1523,7 +1645,10 @@ static int ssh2_pkt_construct(Ssh ssh)
     if (ssh->logctx)
        log_packet(ssh->logctx, PKT_OUTGOING, ssh->pktout.data[5],
                   ssh2_pkt_type(ssh->pkt_ctx, ssh->pktout.data[5]),
-                  ssh->pktout.data + 6, ssh->pktout.length - 6);
+                  ssh->pktout.data + 6, ssh->pktout.length - 6,
+                  ssh->pktout_nblanks, ssh->pktout_blanks);
+    sfree(ssh->pktout_blanks); ssh->pktout_blanks = NULL;
+    ssh->pktout_nblanks = 0;
 
     /*
      * Compress packet payload.
@@ -1828,7 +1953,7 @@ static void ssh_detect_bugs(Ssh ssh, char *vstring)
         (!strcmp(imp, "1.2.18") || !strcmp(imp, "1.2.19") ||
          !strcmp(imp, "1.2.20") || !strcmp(imp, "1.2.21") ||
          !strcmp(imp, "1.2.22") || !strcmp(imp, "Cisco-1.25") ||
-         !strcmp(imp, "OSU_1.4alpha3")))) {
+         !strcmp(imp, "OSU_1.4alpha3") || !strcmp(imp, "OSU_1.5alpha4")))) {
        /*
         * These versions don't support SSH1_MSG_IGNORE, so we have
         * to use a different defence against password length
@@ -2376,8 +2501,10 @@ static void ssh_agentf_callback(void *cv, void *reply, int replylen)
     } else {
        send_packet(ssh, SSH1_MSG_CHANNEL_DATA,
                    PKT_INT, c->remoteid,
+                   PKTT_DATA,
                    PKT_INT, replylen,
                    PKT_DATA, sentreply, replylen,
+                   PKTT_OTHER,
                    PKT_END);
     }
     if (reply)
@@ -3154,10 +3281,11 @@ static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen, int ispkt)
                    randomstr = snewn(top + 1, char);
 
                    for (i = bottom; i <= top; i++) {
-                       if (i == pwlen)
+                       if (i == pwlen) {
                            defer_packet(ssh, s->pwpkt_type,
-                                        PKT_STR, s->password, PKT_END);
-                       else {
+                                        PKTT_PASSWORD, PKT_STR, s->password,
+                                        PKTT_OTHER, PKT_END);
+                       } else {
                            for (j = 0; j < i; j++) {
                                do {
                                    randomstr[j] = random_byte();
@@ -3194,8 +3322,9 @@ static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen, int ispkt)
                        ss = s->password;
                    }
                    logevent("Sending length-padded password");
-                   send_packet(ssh, s->pwpkt_type, PKT_INT, len,
-                               PKT_DATA, ss, len, PKT_END);
+                   send_packet(ssh, s->pwpkt_type, PKTT_PASSWORD,
+                               PKT_INT, len, PKT_DATA, ss, len,
+                               PKTT_OTHER, PKT_END);
                } else {
                    /*
                     * The server has _both_
@@ -3206,11 +3335,14 @@ static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen, int ispkt)
                    int len;
                    len = strlen(s->password);
                    logevent("Sending unpadded password");
-                   send_packet(ssh, s->pwpkt_type, PKT_INT, len,
-                               PKT_DATA, s->password, len, PKT_END);
+                   send_packet(ssh, s->pwpkt_type,
+                               PKTT_PASSWORD, PKT_INT, len,
+                               PKT_DATA, s->password, len,
+                               PKTT_OTHER, PKT_END);
                }
            } else {
-               send_packet(ssh, s->pwpkt_type, PKT_STR, s->password, PKT_END);
+               send_packet(ssh, s->pwpkt_type, PKTT_PASSWORD,
+                           PKT_STR, s->password, PKTT_OTHER, PKT_END);
            }
        }
        logevent("Sent password");
@@ -3282,7 +3414,9 @@ int sshfwd_write(struct ssh_channel *c, char *buf, int len)
     if (ssh->version == 1) {
        send_packet(ssh, SSH1_MSG_CHANNEL_DATA,
                    PKT_INT, c->remoteid,
-                   PKT_INT, len, PKT_DATA, buf, len, PKT_END);
+                   PKTT_DATA,
+                   PKT_INT, len, PKT_DATA, buf, len,
+                   PKTT_OTHER, PKT_END);
        /*
         * In SSH1 we can return 0 here - implying that forwarded
         * connections are never individually throttled - because
@@ -3449,27 +3583,40 @@ static void ssh1_protocol(Ssh ssh, unsigned char *in, int inlen, int ispkt)
                }
            }
            if (sport && dport) {
+               /* Set up a description of the source port. */
+               char *sportdesc = dupprintf("%.*s%.*s%.*s%.*s%d%.*s",
+                       (int)(*saddr?strlen(saddr):0), *saddr?saddr:NULL,
+                       (int)(*saddr?1:0), ":",
+                       (int)(sserv ? strlen(sports) : 0), sports,
+                       sserv, "(", sport, sserv, ")");
                if (type == 'L') {
-                   pfd_addforward(host, dport, *saddr ? saddr : NULL,
-                                  sport, ssh, &ssh->cfg);
-                   logeventf(ssh, "Local port %.*s%.*s%.*s%.*s%d%.*s"
-                             " forwarding to %s:%.*s%.*s%d%.*s",
-                             (int)(*saddr?strlen(saddr):0), *saddr?saddr:NULL,
-                             (int)(*saddr?1:0), ":",
-                             (int)(sserv ? strlen(sports) : 0), sports,
-                             sserv, "(", sport, sserv, ")",
-                             host,
-                             (int)(dserv ? strlen(dports) : 0), dports,
-                             dserv, "(", dport, dserv, ")");
+                   /* Verbose description of the destination port */
+                   char *dportdesc = dupprintf("%s:%.*s%.*s%d%.*s",
+                           host,
+                           (int)(dserv ? strlen(dports) : 0), dports,
+                           dserv, "(", dport, dserv, ")");
+                   const char *err = pfd_addforward(host, dport,
+                                                    *saddr ? saddr : NULL,
+                                                    sport, ssh, &ssh->cfg);
+                   if (err) {
+                       logeventf(ssh, "Local port %s forward to %s"
+                                 " failed: %s", sportdesc, dportdesc, err);
+                   } else {
+                       logeventf(ssh, "Local port %s forwarding to %s",
+                                 sportdesc, dportdesc);
+                   }
+                   sfree(dportdesc);
                } else if (type == 'D') {
-                   pfd_addforward(NULL, -1, *saddr ? saddr : NULL,
-                                  sport, ssh, &ssh->cfg);
-                   logeventf(ssh, "Local port %.*s%.*s%.*s%.*s%d%.*s"
-                             " doing SOCKS dynamic forwarding",
-                             (int)(*saddr?strlen(saddr):0), *saddr?saddr:NULL,
-                             (int)(*saddr?1:0), ":",
-                             (int)(sserv ? strlen(sports) : 0), sports,
-                             sserv, "(", sport, sserv, ")");
+                   const char *err = pfd_addforward(NULL, -1,
+                                                    *saddr ? saddr : NULL,
+                                                    sport, ssh, &ssh->cfg);
+                   if (err) {
+                       logeventf(ssh, "Local port %s SOCKS dynamic forward"
+                                 " setup failed: %s", sportdesc, err);
+                   } else {
+                       logeventf(ssh, "Local port %s doing SOCKS"
+                                 " dynamic forwarding", sportdesc);
+                   }
                } else {
                    struct ssh_rportfwd *pf;
                    pf = snew(struct ssh_rportfwd);
@@ -3512,6 +3659,7 @@ static void ssh1_protocol(Ssh ssh, unsigned char *in, int inlen, int ispkt)
                        logevent("Remote port forwarding enabled");
                    }
                }
+               sfree(sportdesc);
            }
        }
     }
@@ -3914,8 +4062,9 @@ static void ssh1_protocol(Ssh ssh, unsigned char *in, int inlen, int ispkt)
        } else {
            while (inlen > 0) {
                int len = min(inlen, 512);
-               send_packet(ssh, SSH1_CMSG_STDIN_DATA,
-                           PKT_INT, len, PKT_DATA, in, len, PKT_END);
+               send_packet(ssh, SSH1_CMSG_STDIN_DATA, PKTT_DATA,
+                           PKT_INT, len, PKT_DATA, in, len,
+                           PKTT_OTHER, PKT_END);
                in += len;
                inlen -= len;
            }
@@ -4488,6 +4637,10 @@ static int do_ssh2_transport(Ssh ssh, unsigned char *in, int inlen, int ispkt)
              ssh->cscipher->text_name);
     logeventf(ssh, "Initialised %.200s server->client encryption",
              ssh->sccipher->text_name);
+    logeventf(ssh, "Initialised %.200s client->server MAC algorithm",
+             ssh->csmac->text_name);
+    logeventf(ssh, "Initialised %.200s server->client MAC algorithm",
+             ssh->scmac->text_name);
     if (ssh->cscomp->text_name)
        logeventf(ssh, "Initialised %s compression",
                  ssh->cscomp->text_name);
@@ -4555,8 +4708,10 @@ static int ssh2_try_send(struct ssh_channel *c)
            len = c->v.v2.remmaxpkt;
        ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_DATA);
        ssh2_pkt_adduint32(ssh, c->remoteid);
+       dont_log_data(ssh, PKTLOG_OMIT);
        ssh2_pkt_addstring_start(ssh);
        ssh2_pkt_addstring_data(ssh, data, len);
+       end_log_omission(ssh);
        ssh2_pkt_send(ssh);
        bufchain_consume(&c->v.v2.outbuffer, len);
        c->v.v2.remwindow -= len;
@@ -5367,8 +5522,10 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen, int ispkt)
                ssh2_pkt_addstring(ssh, "ssh-connection");      /* service requested */
                ssh2_pkt_addstring(ssh, "password");
                ssh2_pkt_addbool(ssh, FALSE);
+               dont_log_password(ssh, PKTLOG_BLANK);
                ssh2_pkt_addstring(ssh, s->password);
                memset(s->password, 0, sizeof(s->password));
+               end_log_omission(ssh);
                ssh2_pkt_defer(ssh);
                /*
                 * We'll include a string that's an exact multiple of the
@@ -5412,8 +5569,10 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen, int ispkt)
                    ssh2_pkt_adduint32(ssh, s->num_prompts);
                }
                if (s->need_pw) {      /* only add pw if we just got one! */
+                   dont_log_password(ssh, PKTLOG_BLANK);
                    ssh2_pkt_addstring(ssh, s->password);
                    memset(s->password, 0, sizeof(s->password));
+                   end_log_omission(ssh);
                    s->curr_prompt++;
                }
                if (s->curr_prompt >= s->num_prompts) {
@@ -5453,43 +5612,47 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen, int ispkt)
      * point; there's no need to send SERVICE_REQUEST.
      */
 
+    ssh->channels = newtree234(ssh_channelcmp);
+
     /*
-     * So now create a channel with a session in it.
+     * Create the main session channel.
      */
-    ssh->channels = newtree234(ssh_channelcmp);
-    ssh->mainchan = snew(struct ssh_channel);
-    ssh->mainchan->ssh = ssh;
-    ssh->mainchan->localid = alloc_channel_id(ssh);
-    ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_OPEN);
-    ssh2_pkt_addstring(ssh, "session");
-    ssh2_pkt_adduint32(ssh, ssh->mainchan->localid);
-    ssh->mainchan->v.v2.locwindow = OUR_V2_WINSIZE;
-    ssh2_pkt_adduint32(ssh, ssh->mainchan->v.v2.locwindow);/* our window size */
-    ssh2_pkt_adduint32(ssh, 0x4000UL);      /* our max pkt size */
-    ssh2_pkt_send(ssh);
-    crWaitUntilV(ispkt);
-    if (ssh->pktin.type != SSH2_MSG_CHANNEL_OPEN_CONFIRMATION) {
-       bombout(("Server refused to open a session"));
-       crStopV;
-       /* FIXME: error data comes back in FAILURE packet */
-    }
-    if (ssh_pkt_getuint32(ssh) != ssh->mainchan->localid) {
-       bombout(("Server's channel confirmation cited wrong channel"));
-       crStopV;
-    }
-    ssh->mainchan->remoteid = ssh_pkt_getuint32(ssh);
-    ssh->mainchan->type = CHAN_MAINSESSION;
-    ssh->mainchan->closes = 0;
-    ssh->mainchan->v.v2.remwindow = ssh_pkt_getuint32(ssh);
-    ssh->mainchan->v.v2.remmaxpkt = ssh_pkt_getuint32(ssh);
-    bufchain_init(&ssh->mainchan->v.v2.outbuffer);
-    add234(ssh->channels, ssh->mainchan);
-    logevent("Opened channel for session");
+    if (!ssh->cfg.ssh_no_shell) {
+       ssh->mainchan = snew(struct ssh_channel);
+       ssh->mainchan->ssh = ssh;
+       ssh->mainchan->localid = alloc_channel_id(ssh);
+       ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_OPEN);
+       ssh2_pkt_addstring(ssh, "session");
+       ssh2_pkt_adduint32(ssh, ssh->mainchan->localid);
+       ssh->mainchan->v.v2.locwindow = OUR_V2_WINSIZE;
+       ssh2_pkt_adduint32(ssh, ssh->mainchan->v.v2.locwindow);/* our window size */
+       ssh2_pkt_adduint32(ssh, 0x4000UL);      /* our max pkt size */
+       ssh2_pkt_send(ssh);
+       crWaitUntilV(ispkt);
+       if (ssh->pktin.type != SSH2_MSG_CHANNEL_OPEN_CONFIRMATION) {
+           bombout(("Server refused to open a session"));
+           crStopV;
+           /* FIXME: error data comes back in FAILURE packet */
+       }
+       if (ssh_pkt_getuint32(ssh) != ssh->mainchan->localid) {
+           bombout(("Server's channel confirmation cited wrong channel"));
+           crStopV;
+       }
+       ssh->mainchan->remoteid = ssh_pkt_getuint32(ssh);
+       ssh->mainchan->type = CHAN_MAINSESSION;
+       ssh->mainchan->closes = 0;
+       ssh->mainchan->v.v2.remwindow = ssh_pkt_getuint32(ssh);
+       ssh->mainchan->v.v2.remmaxpkt = ssh_pkt_getuint32(ssh);
+       bufchain_init(&ssh->mainchan->v.v2.outbuffer);
+       add234(ssh->channels, ssh->mainchan);
+       logevent("Opened channel for session");
+    } else
+       ssh->mainchan = NULL;
 
     /*
      * Potentially enable X11 forwarding.
      */
-    if (ssh->cfg.x11_forward) {
+    if (ssh->mainchan && ssh->cfg.x11_forward) {
        char proto[20], data[64];
        logevent("Requesting X11 forwarding");
        ssh->x11auth = x11_invent_auth(proto, sizeof(proto),
@@ -5606,27 +5769,40 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen, int ispkt)
                }
            }
            if (sport && dport) {
+               /* Set up a description of the source port. */
+               char *sportdesc = dupprintf("%.*s%.*s%.*s%.*s%d%.*s",
+                       (int)(*saddr?strlen(saddr):0), *saddr?saddr:NULL,
+                       (int)(*saddr?1:0), ":",
+                       (int)(sserv ? strlen(sports) : 0), sports,
+                       sserv, "(", sport, sserv, ")");
                if (type == 'L') {
-                   pfd_addforward(host, dport, *saddr ? saddr : NULL,
-                                  sport, ssh, &ssh->cfg);
-                   logeventf(ssh, "Local port %.*s%.*s%.*s%.*s%d%.*s"
-                             " forwarding to %s:%.*s%.*s%d%.*s",
-                             (int)(*saddr?strlen(saddr):0), *saddr?saddr:NULL,
-                             (int)(*saddr?1:0), ":",
-                             (int)(sserv ? strlen(sports) : 0), sports,
-                             sserv, "(", sport, sserv, ")",
-                             host,
-                             (int)(dserv ? strlen(dports) : 0), dports,
-                             dserv, "(", dport, dserv, ")");
+                   /* Verbose description of the destination port */
+                   char *dportdesc = dupprintf("%s:%.*s%.*s%d%.*s",
+                           host,
+                           (int)(dserv ? strlen(dports) : 0), dports,
+                           dserv, "(", dport, dserv, ")");
+                   const char *err = pfd_addforward(host, dport,
+                                                    *saddr ? saddr : NULL,
+                                                    sport, ssh, &ssh->cfg);
+                   if (err) {
+                       logeventf(ssh, "Local port %s forward to %s"
+                                 " failed: %s", sportdesc, dportdesc, err);
+                   } else {
+                       logeventf(ssh, "Local port %s forwarding to %s",
+                                 sportdesc, dportdesc);
+                   }
+                   sfree(dportdesc);
                } else if (type == 'D') {
-                   pfd_addforward(NULL, -1, *saddr ? saddr : NULL,
-                                  sport, ssh, &ssh->cfg);
-                   logeventf(ssh, "Local port %.*s%.*s%.*s%.*s%d%.*s"
-                             " doing SOCKS dynamic forwarding",
-                             (int)(*saddr?strlen(saddr):0), *saddr?saddr:NULL,
-                             (int)(*saddr?1:0), ":",
-                             (int)(sserv ? strlen(sports) : 0), sports,
-                             sserv, "(", sport, sserv, ")");
+                   const char *err = pfd_addforward(NULL, -1,
+                                                    *saddr ? saddr : NULL,
+                                                    sport, ssh, &ssh->cfg);
+                   if (err) {
+                       logeventf(ssh, "Local port %s SOCKS dynamic forward"
+                                 " setup failed: %s", sportdesc, err);
+                   } else {
+                       logeventf(ssh, "Local port %s doing SOCKS"
+                                 " dynamic forwarding", sportdesc);
+                   }
                } else {
                    struct ssh_rportfwd *pf;
                    pf = snew(struct ssh_rportfwd);
@@ -5638,14 +5814,9 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen, int ispkt)
                                  " to %s:%d", host, dport);
                        sfree(pf);
                    } else {
-                       logeventf(ssh, "Requesting remote port "
-                                 "%.*s%.*s%.*s%.*s%d%.*s"
+                       logeventf(ssh, "Requesting remote port %s"
                                  " forward to %s:%.*s%.*s%d%.*s",
-                                 (int)(*saddr?strlen(saddr):0),
-                                 *saddr?saddr:NULL,
-                                 (int)(*saddr?1:0), ":",
-                                 (int)(sserv ? strlen(sports) : 0), sports,
-                                 sserv, "(", sport, sserv, ")",
+                                 sportdesc,
                                  host,
                                  (int)(dserv ? strlen(dports) : 0), dports,
                                  dserv, "(", dport, dserv, ")");
@@ -5686,6 +5857,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen, int ispkt)
                        }
                    }
                }
+               sfree(sportdesc);
            }
        }
     }
@@ -5693,7 +5865,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen, int ispkt)
     /*
      * Potentially enable agent forwarding.
      */
-    if (ssh->cfg.agentfwd && agent_exists()) {
+    if (ssh->mainchan && ssh->cfg.agentfwd && agent_exists()) {
        logevent("Requesting OpenSSH-style agent forwarding");
        ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_REQUEST);
        ssh2_pkt_adduint32(ssh, ssh->mainchan->remoteid);
@@ -5729,7 +5901,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen, int ispkt)
     /*
      * Now allocate a pty for the session.
      */
-    if (!ssh->cfg.nopty) {
+    if (ssh->mainchan && !ssh->cfg.nopty) {
        /* Unpick the terminal-speed string. */
        /* XXX perhaps we should allow no speeds to be sent. */
         ssh->ospeed = 38400; ssh->ispeed = 38400; /* last-resort defaults */
@@ -5786,7 +5958,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen, int ispkt)
      * this twice if the config data has provided a second choice
      * of command.
      */
-    while (1) {
+    if (ssh->mainchan) while (1) {
        int subsys;
        char *cmd;
 
@@ -5860,7 +6032,8 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen, int ispkt)
      */
     if (ssh->ldisc)
        ldisc_send(ssh->ldisc, NULL, 0, 0);/* cause ldisc to notice changes */
-    ssh->send_ok = 1;
+    if (ssh->mainchan)
+       ssh->send_ok = 1;
     while (1) {
        crReturnV;
        s->try_send = FALSE;
@@ -6003,8 +6176,10 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen, int ispkt)
 
                /*
                 * See if that was the last channel left open.
+                * (This is only our termination condition if we're
+                * not running in -N mode.)
                 */
-               if (count234(ssh->channels) == 0) {
+               if (!ssh->cfg.ssh_no_shell && count234(ssh->channels) == 0) {
                    logevent("All channels closed. Disconnecting");
 #if 0
                     /*
@@ -6062,7 +6237,18 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen, int ispkt)
                    ssh2_pkt_send(ssh);
                }
            } else if (ssh->pktin.type == SSH2_MSG_CHANNEL_OPEN_FAILURE) {
+                static const char *const reasons[] = {
+                    "<unknown reason code>",
+                    "Administratively prohibited",
+                    "Connect failed",
+                    "Unknown channel type",
+                    "Resource shortage",
+                };
                unsigned i = ssh_pkt_getuint32(ssh);
+                unsigned reason_code;
+                char *reason_string;
+                int reason_length;
+                char *message;
                struct ssh_channel *c;
                c = find234(ssh->channels, &i, ssh_channelfind);
                if (!c)
@@ -6070,7 +6256,15 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen, int ispkt)
                if (c->type != CHAN_SOCKDATA_DORMANT)
                    continue;          /* dunno why they're failing this */
 
-               logevent("Forwarded connection refused by server");
+                reason_code = ssh_pkt_getuint32(ssh);
+                if (reason_code >= lenof(reasons))
+                    reason_code = 0; /* ensure reasons[reason_code] in range */
+                ssh_pkt_getstring(ssh, &reason_string, &reason_length);
+                message = dupprintf("Forwarded connection refused by"
+                                    " server: %s [%.*s]", reasons[reason_code],
+                                    reason_length, reason_string);
+               logevent(message);
+                sfree(message);
 
                pfd_close(c->u.pfd.s);
 
@@ -6265,7 +6459,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen, int ispkt)
                bombout(("Strange packet received: type %d", ssh->pktin.type));
                crStopV;
            }
-       } else {
+       } else if (ssh->mainchan) {
            /*
             * We have spare data. Add it to the channel buffer.
             */
@@ -6366,6 +6560,9 @@ static const char *ssh_init(void *frontend_handle, void **backend_handle,
     ssh->deferred_send_data = NULL;
     ssh->deferred_len = 0;
     ssh->deferred_size = 0;
+    ssh->pktout_logmode = PKTLOG_EMIT;
+    ssh->pktout_nblanks = 0;
+    ssh->pktout_blanks = NULL;
     ssh->fallback_cmd = 0;
     ssh->pkt_ctx = 0;
     ssh->x11auth = NULL;
@@ -6582,7 +6779,7 @@ static void ssh_size(void *handle, int width, int height)
                            PKT_INT, ssh->term_height,
                            PKT_INT, ssh->term_width,
                            PKT_INT, 0, PKT_INT, 0, PKT_END);
-           } else {
+           } else if (ssh->mainchan) {
                ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_REQUEST);
                ssh2_pkt_adduint32(ssh, ssh->mainchan->remoteid);
                ssh2_pkt_addstring(ssh, "window-change");
@@ -6644,7 +6841,7 @@ static void ssh_special(void *handle, Telnet_Special code)
        }
        if (ssh->version == 1) {
            send_packet(ssh, SSH1_CMSG_EOF, PKT_END);
-       } else {
+       } else if (ssh->mainchan) {
            ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_EOF);
            ssh2_pkt_adduint32(ssh, ssh->mainchan->remoteid);
            ssh2_pkt_send(ssh);
@@ -6666,7 +6863,7 @@ static void ssh_special(void *handle, Telnet_Special code)
            || ssh->state == SSH_STATE_PREPACKET) return;
        if (ssh->version == 1) {
            logevent("Unable to send BREAK signal in SSH1");
-       } else {
+       } else if (ssh->mainchan) {
            ssh2_pkt_init(ssh, SSH2_MSG_CHANNEL_REQUEST);
            ssh2_pkt_adduint32(ssh, ssh->mainchan->remoteid);
            ssh2_pkt_addstring(ssh, "break");