]> asedeno.scripts.mit.edu Git - PuTTY.git/blobdiff - ssh.c
Fix a build failure coming from the fuzzing branch.
[PuTTY.git] / ssh.c
diff --git a/ssh.c b/ssh.c
index 0b323d322e69f365d6544efa4e99349ad35adeb1..cc503029eaf633b61f37365996291546fb1d8122 100644 (file)
--- a/ssh.c
+++ b/ssh.c
@@ -364,6 +364,7 @@ static void do_ssh2_authconn(Ssh ssh, const unsigned char *in, int inlen,
                             struct Packet *pktin);
 static void ssh2_channel_check_close(struct ssh_channel *c);
 static void ssh_channel_destroy(struct ssh_channel *c);
+static void ssh2_msg_something_unimplemented(Ssh ssh, struct Packet *pktin);
 
 /*
  * Buffer management constants. There are several of these for
@@ -1649,7 +1650,7 @@ static struct Packet *ssh2_rdpkt(Ssh ssh, const unsigned char **data,
 
         /*
          * OpenSSH encrypt-then-MAC mode: the packet length is
-         * unencrypted.
+         * unencrypted, unless the cipher supports length encryption.
          */
        for (st->i = st->len = 0; st->i < 4; st->i++) {
            while ((*datalen) == 0)
@@ -1657,7 +1658,16 @@ static struct Packet *ssh2_rdpkt(Ssh ssh, const unsigned char **data,
            st->pktin->data[st->i] = *(*data)++;
            (*datalen)--;
        }
-       st->len = toint(GET_32BIT(st->pktin->data));
+        /* Cipher supports length decryption, so do it */
+        if (ssh->sccipher && (ssh->sccipher->flags & SSH_CIPHER_SEPARATE_LENGTH)) {
+            /* Keep the packet the same though, so the MAC passes */
+            unsigned char len[4];
+            memcpy(len, st->pktin->data, 4);
+            ssh->sccipher->decrypt_length(ssh->sc_cipher_ctx, len, 4, st->incoming_sequence);
+            st->len = toint(GET_32BIT(len));
+        } else {
+            st->len = toint(GET_32BIT(st->pktin->data));
+        }
 
        /*
         * _Completely_ silly lengths should be stomped on before they
@@ -1825,6 +1835,15 @@ static struct Packet *ssh2_rdpkt(Ssh ssh, const unsigned char **data,
        }
     }
 
+    /*
+     * RFC 4253 doesn't explicitly say that completely empty packets
+     * with no type byte are forbidden, so treat them as deserving
+     * an SSH_MSG_UNIMPLEMENTED.
+     */
+    if (st->pktin->length <= 5) { /* == 5 we hope, but robustness */
+        ssh2_msg_something_unimplemented(ssh, st->pktin);
+        crStop(NULL);
+    }
     /*
      * pktin->body and pktin->length should identify the semantic
      * content of the packet, excluding the initial type byte.
@@ -2277,6 +2296,13 @@ static int ssh2_pkt_construct(Ssh ssh, struct Packet *pkt)
     for (i = 0; i < padding; i++)
        pkt->data[pkt->length + i] = random_byte();
     PUT_32BIT(pkt->data, pkt->length + padding - 4);
+
+    /* Encrypt length if the scheme requires it */
+    if (ssh->cscipher && (ssh->cscipher->flags & SSH_CIPHER_SEPARATE_LENGTH)) {
+        ssh->cscipher->encrypt_length(ssh->cs_cipher_ctx, pkt->data, 4,
+                                      ssh->v2_outgoing_sequence);
+    }
+
     if (ssh->csmac && ssh->csmac_etm) {
         /*
          * OpenSSH-defined encrypt-then-MAC protocol.
@@ -2991,6 +3017,10 @@ static void ssh_send_verstring(Ssh ssh, const char *protoname, char *svers)
     }
 
     ssh_fix_verstring(verstring + strlen(protoname));
+#ifdef FUZZING
+    /* FUZZING make PuTTY insecure, so make live use difficult. */
+    verstring[0] = 'I';
+#endif
 
     if (ssh->version == 2) {
        size_t len;
@@ -3533,35 +3563,20 @@ static void ssh_sent(Plug plug, int bufsize)
        ssh_throttle_all(ssh, 0, bufsize);
 }
 
-/*
- * Connect to specified host and port.
- * Returns an error message, or NULL on success.
- * Also places the canonical host name into `realhost'. It must be
- * freed by the caller.
- */
-static const char *connect_to_host(Ssh ssh, const char *host, int port,
-                                  char **realhost, int nodelay, int keepalive)
+static void ssh_hostport_setup(const char *host, int port, Conf *conf,
+                               char **savedhost, int *savedport,
+                               char **loghost_ret)
 {
-    static const struct plug_function_table fn_table = {
-       ssh_socket_log,
-       ssh_closing,
-       ssh_receive,
-       ssh_sent,
-       NULL
-    };
+    char *loghost = conf_get_str(conf, CONF_loghost);
+    if (loghost_ret)
+        *loghost_ret = loghost;
 
-    SockAddr addr;
-    const char *err;
-    char *loghost;
-    int addressfamily, sshprot;
-    
-    loghost = conf_get_str(ssh->conf, CONF_loghost);
     if (*loghost) {
        char *tmphost;
         char *colon;
 
         tmphost = dupstr(loghost);
-       ssh->savedport = 22;           /* default ssh port */
+       *savedport = 22;               /* default ssh port */
 
        /*
         * A colon suffix on the hostname string also lets us affect
@@ -3572,17 +3587,58 @@ static const char *connect_to_host(Ssh ssh, const char *host, int port,
        if (colon && colon == host_strchr(tmphost, ':')) {
            *colon++ = '\0';
            if (*colon)
-               ssh->savedport = atoi(colon);
+               *savedport = atoi(colon);
        }
 
-        ssh->savedhost = host_strduptrim(tmphost);
+        *savedhost = host_strduptrim(tmphost);
         sfree(tmphost);
     } else {
-       ssh->savedhost = host_strduptrim(host);
+       *savedhost = host_strduptrim(host);
        if (port < 0)
            port = 22;                 /* default ssh port */
-       ssh->savedport = port;
+       *savedport = port;
     }
+}
+
+static int ssh_test_for_upstream(const char *host, int port, Conf *conf)
+{
+    char *savedhost;
+    int savedport;
+    int ret;
+
+    random_ref(); /* platform may need this to determine share socket name */
+    ssh_hostport_setup(host, port, conf, &savedhost, &savedport, NULL);
+    ret = ssh_share_test_for_upstream(savedhost, savedport, conf);
+    sfree(savedhost);
+    random_unref();
+
+    return ret;
+}
+
+/*
+ * Connect to specified host and port.
+ * Returns an error message, or NULL on success.
+ * Also places the canonical host name into `realhost'. It must be
+ * freed by the caller.
+ */
+static const char *connect_to_host(Ssh ssh, const char *host, int port,
+                                  char **realhost, int nodelay, int keepalive)
+{
+    static const struct plug_function_table fn_table = {
+       ssh_socket_log,
+       ssh_closing,
+       ssh_receive,
+       ssh_sent,
+       NULL
+    };
+
+    SockAddr addr;
+    const char *err;
+    char *loghost;
+    int addressfamily, sshprot;
+
+    ssh_hostport_setup(host, port, ssh->conf,
+                       &ssh->savedhost, &ssh->savedport, &loghost);
 
     ssh->fn = &fn_table;               /* make 'ssh' usable as a Plug */
 
@@ -3998,6 +4054,9 @@ static int do_ssh1_login(Ssh ssh, const unsigned char *in, int inlen,
                                             "rsa", keystr, fingerprint,
                                             ssh_dialog_callback, ssh);
             sfree(keystr);
+#ifdef FUZZING
+           s->dlgret = 1;
+#endif
             if (s->dlgret < 0) {
                 do {
                     crReturn(0);
@@ -6111,16 +6170,24 @@ static void ssh2_pkt_addstring_commasep(struct Packet *pkt, const char *data)
 
 
 /*
- * SSH-2 key creation method.
- * (Currently assumes 2 lots of any hash are sufficient to generate
- * keys/IVs for any cipher/MAC. SSH2_MKKEY_ITERS documents this assumption.)
+ * SSH-2 key derivation (RFC 4253 section 7.2).
  */
-#define SSH2_MKKEY_ITERS (2)
-static void ssh2_mkkey(Ssh ssh, Bignum K, unsigned char *H, char chr,
-                      unsigned char *keyspace)
+static unsigned char *ssh2_mkkey(Ssh ssh, Bignum K, unsigned char *H,
+                                 char chr, int keylen)
 {
     const struct ssh_hash *h = ssh->kex->hash;
-    void *s;
+    int keylen_padded;
+    unsigned char *key;
+    void *s, *s2;
+
+    if (keylen == 0)
+        return NULL;
+
+    /* Round up to the next multiple of hash length. */
+    keylen_padded = ((keylen + h->hlen - 1) / h->hlen) * h->hlen;
+
+    key = snewn(keylen_padded, unsigned char);
+
     /* First hlen bytes. */
     s = h->init();
     if (!(ssh->remote_bugs & BUG_SSH2_DERIVEKEY))
@@ -6128,14 +6195,33 @@ static void ssh2_mkkey(Ssh ssh, Bignum K, unsigned char *H, char chr,
     h->bytes(s, H, h->hlen);
     h->bytes(s, &chr, 1);
     h->bytes(s, ssh->v2_session_id, ssh->v2_session_id_len);
-    h->final(s, keyspace);
-    /* Next hlen bytes. */
-    s = h->init();
-    if (!(ssh->remote_bugs & BUG_SSH2_DERIVEKEY))
-       hash_mpint(h, s, K);
-    h->bytes(s, H, h->hlen);
-    h->bytes(s, keyspace, h->hlen);
-    h->final(s, keyspace + h->hlen);
+    h->final(s, key);
+
+    /* Subsequent blocks of hlen bytes. */
+    if (keylen_padded > h->hlen) {
+        int offset;
+
+        s = h->init();
+        if (!(ssh->remote_bugs & BUG_SSH2_DERIVEKEY))
+            hash_mpint(h, s, K);
+        h->bytes(s, H, h->hlen);
+
+        for (offset = h->hlen; offset < keylen_padded; offset += h->hlen) {
+            h->bytes(s, key + offset - h->hlen, h->hlen);
+            s2 = h->copy(s);
+            h->final(s2, key + offset);
+        }
+
+        h->free(s);
+    }
+
+    /* Now clear any extra bytes of key material beyond the length
+     * we're officially returning, because the caller won't know to
+     * smemclr those. */
+    if (keylen_padded > keylen)
+        smemclr(key + keylen, keylen_padded - keylen);
+
+    return key;
 }
 
 /*
@@ -6181,6 +6267,7 @@ static struct kexinit_algorithm *ssh2_kexinit_addalg(struct kexinit_algorithm
            return &list[i];
        }
     assert(!"No space in KEXINIT list");
+    return NULL;
 }
 
 /*
@@ -6324,6 +6411,9 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
              case CIPHER_ARCFOUR:
                s->preferred_ciphers[s->n_preferred_ciphers++] = &ssh2_arcfour;
                break;
+              case CIPHER_CHACHA20:
+                s->preferred_ciphers[s->n_preferred_ciphers++] = &ssh2_ccp;
+                break;
              case CIPHER_WARN:
                /* Flag for later. Don't bother if it's the last in
                 * the list. */
@@ -6404,6 +6494,11 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
        /* List encryption algorithms (client->server then server->client). */
        for (k = KEXLIST_CSCIPHER; k <= KEXLIST_SCCIPHER; k++) {
            warn = FALSE;
+#ifdef FUZZING
+           alg = ssh2_kexinit_addalg(s->kexlists[k], "none");
+           alg->u.cipher.cipher = NULL;
+           alg->u.cipher.warn = warn;
+#endif /* FUZZING */
            for (i = 0; i < s->n_preferred_ciphers; i++) {
                const struct ssh2_ciphers *c = s->preferred_ciphers[i];
                if (!c) warn = TRUE;
@@ -6417,6 +6512,11 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
        }
        /* List MAC algorithms (client->server then server->client). */
        for (j = KEXLIST_CSMAC; j <= KEXLIST_SCMAC; j++) {
+#ifdef FUZZING
+           alg = ssh2_kexinit_addalg(s->kexlists[j], "none");
+           alg->u.mac.mac = NULL;
+           alg->u.mac.etm = FALSE;
+#endif /* FUZZING */
            for (i = 0; i < s->nmacs; i++) {
                alg = ssh2_kexinit_addalg(s->kexlists[j], s->maclist[i]->name);
                alg->u.mac.mac = s->maclist[i];
@@ -6521,6 +6621,24 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
                bombout(("KEXINIT packet was incomplete"));
                crStopV;
            }
+
+            /* If we've already selected a cipher which requires a
+             * particular MAC, then just select that, and don't even
+             * bother looking through the server's KEXINIT string for
+             * MACs. */
+            if (i == KEXLIST_CSMAC && s->cscipher_tobe &&
+                s->cscipher_tobe->required_mac) {
+                s->csmac_tobe = s->cscipher_tobe->required_mac;
+                s->csmac_etm_tobe = !!(s->csmac_tobe->etm_name);
+                goto matched;
+            }
+            if (i == KEXLIST_SCMAC && s->sccipher_tobe &&
+                s->sccipher_tobe->required_mac) {
+                s->scmac_tobe = s->sccipher_tobe->required_mac;
+                s->scmac_etm_tobe = !!(s->scmac_tobe->etm_name);
+                goto matched;
+            }
+
            for (j = 0; j < MAXKEXLIST; j++) {
                struct kexinit_algorithm *alg = &s->kexlists[i][j];
                if (alg->name == NULL) break;
@@ -6566,16 +6684,6 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
          matched:;
        }
 
-        /* If the cipher over-rides the mac, then pick it */
-        if (s->cscipher_tobe && s->cscipher_tobe->required_mac) {
-            s->csmac_tobe = s->cscipher_tobe->required_mac;
-           s->csmac_etm_tobe = !!(s->csmac_tobe->etm_name);
-        }
-        if (s->sccipher_tobe && s->sccipher_tobe->required_mac) {
-            s->scmac_tobe = s->sccipher_tobe->required_mac;
-           s->scmac_etm_tobe = !!(s->scmac_tobe->etm_name);
-        }
-
        if (s->pending_compression) {
            logevent("Server supports delayed compression; "
                     "will try this later");
@@ -6681,8 +6789,8 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
         {
             int csbits, scbits;
 
-            csbits = s->cscipher_tobe->keylen;
-            scbits = s->sccipher_tobe->keylen;
+            csbits = s->cscipher_tobe ? s->cscipher_tobe->real_keybits : 0;
+            scbits = s->sccipher_tobe ? s->sccipher_tobe->real_keybits : 0;
             s->nbits = (csbits > scbits ? csbits : scbits);
         }
         /* The keys only have hlen-bit entropy, since they're based on
@@ -6759,6 +6867,10 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
         }
         set_busy_status(ssh->frontend, BUSY_CPU); /* cogitate */
         ssh_pkt_getstring(pktin, &s->hostkeydata, &s->hostkeylen);
+        if (!s->hostkeydata) {
+            bombout(("unable to parse key exchange reply packet"));
+            crStopV;
+        }
         s->hkey = ssh->hostkey->newkey(ssh->hostkey,
                                        s->hostkeydata, s->hostkeylen);
         s->f = ssh2_pkt_getmp(pktin);
@@ -6767,6 +6879,10 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
             crStopV;
         }
         ssh_pkt_getstring(pktin, &s->sigdata, &s->siglen);
+        if (!s->sigdata) {
+            bombout(("unable to parse key exchange reply packet"));
+            crStopV;
+        }
 
         {
             const char *err = dh_validate_f(ssh->kex_ctx, s->f);
@@ -6838,6 +6954,10 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
         }
 
         ssh_pkt_getstring(pktin, &s->hostkeydata, &s->hostkeylen);
+        if (!s->hostkeydata) {
+            bombout(("unable to parse ECDH reply packet"));
+            crStopV;
+        }
         hash_string(ssh->kex->hash, ssh->exhash, s->hostkeydata, s->hostkeylen);
         s->hkey = ssh->hostkey->newkey(ssh->hostkey,
                                        s->hostkeydata, s->hostkeylen);
@@ -6860,6 +6980,10 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
             char *keydata;
             int keylen;
             ssh_pkt_getstring(pktin, &keydata, &keylen);
+            if (!keydata) {
+                bombout(("unable to parse ECDH reply packet"));
+                crStopV;
+            }
             hash_string(ssh->kex->hash, ssh->exhash, keydata, keylen);
             s->K = ssh_ecdhkex_getkey(s->eckey, keydata, keylen);
             if (!s->K) {
@@ -6870,6 +6994,10 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
         }
 
         ssh_pkt_getstring(pktin, &s->sigdata, &s->siglen);
+        if (!s->sigdata) {
+            bombout(("unable to parse key exchange reply packet"));
+            crStopV;
+        }
 
         ssh_ecdhkex_freekey(s->eckey);
     } else {
@@ -6887,6 +7015,10 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
         }
 
         ssh_pkt_getstring(pktin, &s->hostkeydata, &s->hostkeylen);
+        if (!s->hostkeydata) {
+            bombout(("unable to parse RSA public key packet"));
+            crStopV;
+        }
         hash_string(ssh->kex->hash, ssh->exhash,
                    s->hostkeydata, s->hostkeylen);
        s->hkey = ssh->hostkey->newkey(ssh->hostkey,
@@ -6895,6 +7027,10 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
         {
             char *keydata;
             ssh_pkt_getstring(pktin, &keydata, &s->rsakeylen);
+            if (!keydata) {
+                bombout(("unable to parse RSA public key packet"));
+                crStopV;
+            }
             s->rsakeydata = snewn(s->rsakeylen, char);
             memcpy(s->rsakeydata, keydata, s->rsakeylen);
         }
@@ -6971,6 +7107,10 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
         }
 
         ssh_pkt_getstring(pktin, &s->sigdata, &s->siglen);
+        if (!s->sigdata) {
+            bombout(("unable to parse signature packet"));
+            crStopV;
+        }
 
         sfree(s->rsakeydata);
     }
@@ -6986,12 +7126,18 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
     dmemdump(s->exchange_hash, ssh->kex->hash->hlen);
 #endif
 
-    if (!s->hkey ||
-       !ssh->hostkey->verifysig(s->hkey, s->sigdata, s->siglen,
+    if (!s->hkey) {
+       bombout(("Server's host key is invalid"));
+       crStopV;
+    }
+
+    if (!ssh->hostkey->verifysig(s->hkey, s->sigdata, s->siglen,
                                 (char *)s->exchange_hash,
                                 ssh->kex->hash->hlen)) {
+#ifndef FUZZING
        bombout(("Server's host key did not match the signature supplied"));
        crStopV;
+#endif
     }
 
     s->keystr = ssh->hostkey->fmtkey(s->hkey);
@@ -7016,6 +7162,9 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
                                             ssh->hostkey->keytype, s->keystr,
                                             s->fingerprint,
                                             ssh_dialog_callback, ssh);
+#ifdef FUZZING
+           s->dlgret = 1;
+#endif
             if (s->dlgret < 0) {
                 do {
                     crReturnV;
@@ -7048,8 +7197,10 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
          * the one we saw before.
          */
         if (strcmp(ssh->hostkey_str, s->keystr)) {
+#ifndef FUZZING
             bombout(("Host key was different in repeat key exchange"));
             crStopV;
+#endif
         }
         sfree(s->keystr);
     }
@@ -7083,13 +7234,14 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
     if (ssh->cs_cipher_ctx)
        ssh->cscipher->free_context(ssh->cs_cipher_ctx);
     ssh->cscipher = s->cscipher_tobe;
-    ssh->cs_cipher_ctx = ssh->cscipher->make_context();
+    if (ssh->cscipher) ssh->cs_cipher_ctx = ssh->cscipher->make_context();
 
     if (ssh->cs_mac_ctx)
        ssh->csmac->free_context(ssh->cs_mac_ctx);
     ssh->csmac = s->csmac_tobe;
     ssh->csmac_etm = s->csmac_etm_tobe;
-    ssh->cs_mac_ctx = ssh->csmac->make_context(ssh->cs_cipher_ctx);
+    if (ssh->csmac)
+        ssh->cs_mac_ctx = ssh->csmac->make_context(ssh->cs_cipher_ctx);
 
     if (ssh->cs_comp_ctx)
        ssh->cscomp->compress_cleanup(ssh->cs_comp_ctx);
@@ -7100,29 +7252,39 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
      * Set IVs on client-to-server keys. Here we use the exchange
      * hash from the _first_ key exchange.
      */
-    {
-       unsigned char keyspace[SSH2_KEX_MAX_HASH_LEN * SSH2_MKKEY_ITERS];
-       assert(sizeof(keyspace) >= ssh->kex->hash->hlen * SSH2_MKKEY_ITERS);
-       ssh2_mkkey(ssh,s->K,s->exchange_hash,'C',keyspace);
-       assert((ssh->cscipher->keylen+7) / 8 <=
-              ssh->kex->hash->hlen * SSH2_MKKEY_ITERS);
-       ssh->cscipher->setkey(ssh->cs_cipher_ctx, keyspace);
-       ssh2_mkkey(ssh,s->K,s->exchange_hash,'A',keyspace);
-       assert(ssh->cscipher->blksize <=
-              ssh->kex->hash->hlen * SSH2_MKKEY_ITERS);
-       ssh->cscipher->setiv(ssh->cs_cipher_ctx, keyspace);
-       ssh2_mkkey(ssh,s->K,s->exchange_hash,'E',keyspace);
-       assert(ssh->csmac->len <=
-              ssh->kex->hash->hlen * SSH2_MKKEY_ITERS);
-       ssh->csmac->setkey(ssh->cs_mac_ctx, keyspace);
-       smemclr(keyspace, sizeof(keyspace));
-    }
-
-    logeventf(ssh, "Initialised %.200s client->server encryption",
-             ssh->cscipher->text_name);
-    logeventf(ssh, "Initialised %.200s client->server MAC algorithm%s",
-             ssh->csmac->text_name,
-              ssh->csmac_etm ? " (in ETM mode)" : "");
+    if (ssh->cscipher) {
+       unsigned char *key;
+
+       key = ssh2_mkkey(ssh, s->K, s->exchange_hash, 'C',
+                         ssh->cscipher->padded_keybytes);
+       ssh->cscipher->setkey(ssh->cs_cipher_ctx, key);
+        smemclr(key, ssh->cscipher->padded_keybytes);
+        sfree(key);
+
+       key = ssh2_mkkey(ssh, s->K, s->exchange_hash, 'A',
+                         ssh->cscipher->blksize);
+       ssh->cscipher->setiv(ssh->cs_cipher_ctx, key);
+        smemclr(key, ssh->cscipher->blksize);
+        sfree(key);
+    }
+    if (ssh->csmac) {
+       unsigned char *key;
+
+       key = ssh2_mkkey(ssh, s->K, s->exchange_hash, 'E',
+                         ssh->csmac->keylen);
+       ssh->csmac->setkey(ssh->cs_mac_ctx, key);
+        smemclr(key, ssh->csmac->keylen);
+        sfree(key);
+    }
+
+    if (ssh->cscipher)
+       logeventf(ssh, "Initialised %.200s client->server encryption",
+                 ssh->cscipher->text_name);
+    if (ssh->csmac)
+       logeventf(ssh, "Initialised %.200s client->server MAC algorithm%s%s",
+                 ssh->csmac->text_name,
+                 ssh->csmac_etm ? " (in ETM mode)" : "",
+                 ssh->cscipher->required_mac ? " (required by cipher)" : "");
     if (ssh->cscomp->text_name)
        logeventf(ssh, "Initialised %s compression",
                  ssh->cscomp->text_name);
@@ -7150,14 +7312,18 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
      */
     if (ssh->sc_cipher_ctx)
        ssh->sccipher->free_context(ssh->sc_cipher_ctx);
-    ssh->sccipher = s->sccipher_tobe;
-    ssh->sc_cipher_ctx = ssh->sccipher->make_context();
+    if (ssh->sccipher) {
+       ssh->sccipher = s->sccipher_tobe;
+       ssh->sc_cipher_ctx = ssh->sccipher->make_context();
+    }
 
     if (ssh->sc_mac_ctx)
        ssh->scmac->free_context(ssh->sc_mac_ctx);
-    ssh->scmac = s->scmac_tobe;
-    ssh->scmac_etm = s->scmac_etm_tobe;
-    ssh->sc_mac_ctx = ssh->scmac->make_context(ssh->sc_cipher_ctx);
+    if (ssh->scmac) {
+       ssh->scmac = s->scmac_tobe;
+       ssh->scmac_etm = s->scmac_etm_tobe;
+       ssh->sc_mac_ctx = ssh->scmac->make_context(ssh->sc_cipher_ctx);
+    }
 
     if (ssh->sc_comp_ctx)
        ssh->sccomp->decompress_cleanup(ssh->sc_comp_ctx);
@@ -7168,28 +7334,38 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
      * Set IVs on server-to-client keys. Here we use the exchange
      * hash from the _first_ key exchange.
      */
-    {
-       unsigned char keyspace[SSH2_KEX_MAX_HASH_LEN * SSH2_MKKEY_ITERS];
-       assert(sizeof(keyspace) >= ssh->kex->hash->hlen * SSH2_MKKEY_ITERS);
-       ssh2_mkkey(ssh,s->K,s->exchange_hash,'D',keyspace);
-       assert((ssh->sccipher->keylen+7) / 8 <=
-              ssh->kex->hash->hlen * SSH2_MKKEY_ITERS);
-       ssh->sccipher->setkey(ssh->sc_cipher_ctx, keyspace);
-       ssh2_mkkey(ssh,s->K,s->exchange_hash,'B',keyspace);
-       assert(ssh->sccipher->blksize <=
-              ssh->kex->hash->hlen * SSH2_MKKEY_ITERS);
-       ssh->sccipher->setiv(ssh->sc_cipher_ctx, keyspace);
-       ssh2_mkkey(ssh,s->K,s->exchange_hash,'F',keyspace);
-       assert(ssh->scmac->len <=
-              ssh->kex->hash->hlen * SSH2_MKKEY_ITERS);
-       ssh->scmac->setkey(ssh->sc_mac_ctx, keyspace);
-       smemclr(keyspace, sizeof(keyspace));
-    }
-    logeventf(ssh, "Initialised %.200s server->client encryption",
-             ssh->sccipher->text_name);
-    logeventf(ssh, "Initialised %.200s server->client MAC algorithm%s",
-             ssh->scmac->text_name,
-              ssh->scmac_etm ? " (in ETM mode)" : "");
+    if (ssh->sccipher) {
+       unsigned char *key;
+
+       key = ssh2_mkkey(ssh, s->K, s->exchange_hash, 'D',
+                         ssh->sccipher->padded_keybytes);
+       ssh->sccipher->setkey(ssh->sc_cipher_ctx, key);
+        smemclr(key, ssh->sccipher->padded_keybytes);
+        sfree(key);
+
+       key = ssh2_mkkey(ssh, s->K, s->exchange_hash, 'B',
+                         ssh->sccipher->blksize);
+       ssh->sccipher->setiv(ssh->sc_cipher_ctx, key);
+        smemclr(key, ssh->sccipher->blksize);
+        sfree(key);
+    }
+    if (ssh->scmac) {
+       unsigned char *key;
+
+       key = ssh2_mkkey(ssh, s->K, s->exchange_hash, 'F',
+                         ssh->scmac->keylen);
+       ssh->scmac->setkey(ssh->sc_mac_ctx, key);
+        smemclr(key, ssh->scmac->keylen);
+        sfree(key);
+    }
+    if (ssh->sccipher)
+       logeventf(ssh, "Initialised %.200s server->client encryption",
+                 ssh->sccipher->text_name);
+    if (ssh->scmac)
+       logeventf(ssh, "Initialised %.200s server->client MAC algorithm%s%s",
+                 ssh->scmac->text_name,
+                 ssh->scmac_etm ? " (in ETM mode)" : "",
+                 ssh->sccipher->required_mac ? " (required by cipher)" : "");
     if (ssh->sccomp->text_name)
        logeventf(ssh, "Initialised %s decompression",
                  ssh->sccomp->text_name);
@@ -7764,7 +7940,7 @@ static void ssh_check_termination(Ssh ssh)
 {
     if (ssh->version == 2 &&
         !conf_get_int(ssh->conf, CONF_ssh_no_shell) &&
-        count234(ssh->channels) == 0 &&
+        (ssh->channels && count234(ssh->channels) == 0) &&
         !(ssh->connshare && share_ndownstreams(ssh->connshare) > 0)) {
         /*
          * We used to send SSH_MSG_DISCONNECT here, because I'd
@@ -9305,11 +9481,20 @@ static void do_ssh2_authconn(Ssh ssh, const unsigned char *in, int inlen,
                s->can_keyb_inter = conf_get_int(ssh->conf, CONF_try_ki_auth) &&
                    in_commasep_string("keyboard-interactive", methods, methlen);
 #ifndef NO_GSSAPI
-               if (!ssh->gsslibs)
-                   ssh->gsslibs = ssh_gss_setup(ssh->conf);
-               s->can_gssapi = conf_get_int(ssh->conf, CONF_try_gssapi_auth) &&
-                   in_commasep_string("gssapi-with-mic", methods, methlen) &&
-                   ssh->gsslibs->nlibraries > 0;
+                if (conf_get_int(ssh->conf, CONF_try_gssapi_auth) &&
+                   in_commasep_string("gssapi-with-mic", methods, methlen)) {
+                    /* Try loading the GSS libraries and see if we
+                     * have any. */
+                    if (!ssh->gsslibs)
+                        ssh->gsslibs = ssh_gss_setup(ssh->conf);
+                    s->can_gssapi = (ssh->gsslibs->nlibraries > 0);
+                } else {
+                    /* No point in even bothering to try to load the
+                     * GSS libraries, if the user configuration and
+                     * server aren't both prepared to attempt GSSAPI
+                     * auth in the first place. */
+                    s->can_gssapi = FALSE;
+                }
 #endif
            }
 
@@ -10503,7 +10688,8 @@ static void do_ssh2_authconn(Ssh ssh, const unsigned char *in, int inlen,
             * Try to send data on all channels if we can.
             */
            for (i = 0; NULL != (c = index234(ssh->channels, i)); i++)
-               ssh2_try_send_and_unthrottle(ssh, c);
+                if (c->type != CHAN_SHARING)
+                    ssh2_try_send_and_unthrottle(ssh, c);
        }
     }
 
@@ -11527,6 +11713,7 @@ Backend ssh_backend = {
     ssh_provide_logctx,
     ssh_unthrottle,
     ssh_cfg_info,
+    ssh_test_for_upstream,
     "ssh",
     PROT_SSH,
     22