X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=blobdiff_plain;f=ssh.c;h=5d6514b5ae7829509c8001f435517d1e44061c6f;hb=0629f1dfa53fe63bce41eaefd9358ea8c7227eeb;hp=e6acec6271f3848f10271a7001a82c9efbbe3bdd;hpb=5de81cb0356187a8dff7b776b9f6abcee2ed0e91;p=PuTTY.git

diff --git a/ssh.c b/ssh.c
index e6acec62..5d6514b5 100644
--- a/ssh.c
+++ b/ssh.c
@@ -1649,7 +1649,7 @@ 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 +1657,16 @@ 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
@@ -2277,6 +2286,13 @@ 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.
@@ -3533,35 +3549,20 @@ 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 +3573,58 @@ 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 */
 
@@ -6058,39 +6100,7 @@ static void ssh1_protocol(Ssh ssh, const void *vin, int inlen,
 }
 
 /*
- * Utility routine for decoding comma-separated strings in KEXINIT.
- */
-static int in_commasep_string(char const *needle, char const *haystack,
-			      int haylen)
-{
-    int needlen;
-    if (!needle || !haystack)	       /* protect against null pointers */
-	return 0;
-    needlen = strlen(needle);
-    while (1) {
-	/*
-	 * Is it at the start of the string?
-	 */
-	if (haylen >= needlen &&       /* haystack is long enough */
-	    !memcmp(needle, haystack, needlen) &&	/* initial match */
-	    (haylen == needlen || haystack[needlen] == ',')
-	    /* either , or EOS follows */
-	    )
-	    return 1;
-	/*
-	 * If not, search for the next comma and resume after that.
-	 * If no comma found, terminate.
-	 */
-	while (haylen > 0 && *haystack != ',')
-	    haylen--, haystack++;
-	if (haylen == 0)
-	    return 0;
-	haylen--, haystack++;	       /* skip over comma itself */
-    }
-}
-
-/*
- * Similar routine for checking whether we have the first string in a list.
+ * Utility routines for decoding comma-separated strings in KEXINIT.
  */
 static int first_in_commasep_string(char const *needle, char const *haystack,
 				    int haylen)
@@ -6099,9 +6109,7 @@ static int first_in_commasep_string(char const *needle, char const *haystack,
     if (!needle || !haystack)	       /* protect against null pointers */
 	return 0;
     needlen = strlen(needle);
-    /*
-     * Is it at the start of the string?
-     */
+
     if (haylen >= needlen &&       /* haystack is long enough */
 	!memcmp(needle, haystack, needlen) &&	/* initial match */
 	(haylen == needlen || haystack[needlen] == ',')
@@ -6111,14 +6119,33 @@ static int first_in_commasep_string(char const *needle, char const *haystack,
     return 0;
 }
 
+static int in_commasep_string(char const *needle, char const *haystack,
+			      int haylen)
+{
+    char *p;
+
+    if (!needle || !haystack)	       /* protect against null pointers */
+	return 0;
+    /*
+     * Is it at the start of the string?
+     */
+    if (first_in_commasep_string(needle, haystack, haylen))
+	return 1;
+    /*
+     * If not, search for the next comma and resume after that.
+     * If no comma found, terminate.
+     */
+    p = memchr(haystack, ',', haylen);
+    if (!p) return 0;
+    /* + 1 to skip over comma */
+    return in_commasep_string(needle, p + 1, haylen - (p + 1 - haystack));
+}
+
 /*
  * Add a value to the comma-separated string at the end of the packet.
- * If the value is already in the string, don't bother adding it again.
  */
 static void ssh2_pkt_addstring_commasep(struct Packet *pkt, const char *data)
 {
-    if (in_commasep_string(data, (char *)pkt->data + pkt->savedpos,
-			   pkt->length - pkt->savedpos)) return;
     if (pkt->length - pkt->savedpos > 0)
 	ssh_pkt_addstring_str(pkt, ",");
     ssh_pkt_addstring_str(pkt, data);
@@ -6126,16 +6153,24 @@ 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))
@@ -6143,14 +6178,79 @@ 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;
+}
+
+/*
+ * Structure for constructing KEXINIT algorithm lists.
+ */
+#define MAXKEXLIST 16
+struct kexinit_algorithm {
+    const char *name;
+    union {
+	struct {
+	    const struct ssh_kex *kex;
+	    int warn;
+	} kex;
+	const struct ssh_signkey *hostkey;
+	struct {
+	    const struct ssh2_cipher *cipher;
+	    int warn;
+	} cipher;
+	struct {
+	    const struct ssh_mac *mac;
+	    int etm;
+	} mac;
+	const struct ssh_compress *comp;
+    } u;
+};
+
+/*
+ * Find a slot in a KEXINIT algorithm list to use for a new algorithm.
+ * If the algorithm is already in the list, return a pointer to its
+ * entry, otherwise return an entry from the end of the list.
+ * This assumes that every time a particular name is passed in, it
+ * comes from the same string constant.  If this isn't true, this
+ * function may need to be rewritten to use strcmp() instead.
+ */
+static struct kexinit_algorithm *ssh2_kexinit_addalg(struct kexinit_algorithm
+						     *list, const char *name)
+{
+    int i;
+
+    for (i = 0; i < MAXKEXLIST; i++)
+	if (list[i].name == NULL || list[i].name == name) {
+	    list[i].name = name;
+	    return &list[i];
+	}
+    assert(!"No space in KEXINIT list");
+    return NULL;
 }
 
 /*
@@ -6205,26 +6305,7 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
         int dlgret;
 	int guessok;
 	int ignorepkt;
-#define MAXKEXLIST 16
-	struct kexinit_algorithm {
-	    const char *name;
-	    union {
-	        struct {
-		    const struct ssh_kex *kex;
-		    int warn;
-		} kex;
-	        const struct ssh_signkey *hostkey;
-		struct {
-		    const struct ssh2_cipher *cipher;
-		    int warn;
-		} cipher;
-	        struct {
-		    const struct ssh_mac *mac;
-		    int etm;
-		} mac;
-	        const struct ssh_compress *comp;
-            } u;
-        } kexlists[NKEXLIST][MAXKEXLIST];
+	struct kexinit_algorithm kexlists[NKEXLIST][MAXKEXLIST];
     };
     crState(do_ssh2_transport_state);
 
@@ -6251,7 +6332,8 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
   begin_key_exchange:
     ssh->pkt_kctx = SSH2_PKTCTX_NOKEX;
     {
-	int i, j, k, n, warn;
+	int i, j, k, warn;
+	struct kexinit_algorithm *alg;
 
 	/*
 	 * Set up the preferred key exchange. (NULL => warn below here)
@@ -6312,6 +6394,9 @@ 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. */
@@ -6345,31 +6430,36 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
 	    for (j = 0; j < MAXKEXLIST; j++)
 	        s->kexlists[i][j].name = NULL;
 	/* List key exchange algorithms. */
-	n = 0;
 	warn = FALSE;
 	for (i = 0; i < s->n_preferred_kex; i++) {
 	    const struct ssh_kexes *k = s->preferred_kex[i];
 	    if (!k) warn = TRUE;
 	    else for (j = 0; j < k->nkexes; j++) {
-	        assert(n < MAXKEXLIST);
-	        s->kexlists[KEXLIST_KEX][n].name = k->list[j]->name;
-		s->kexlists[KEXLIST_KEX][n].u.kex.kex = k->list[j];
-		s->kexlists[KEXLIST_KEX][n].u.kex.warn = warn;
-		n++;
+		alg = ssh2_kexinit_addalg(s->kexlists[KEXLIST_KEX],
+					  k->list[j]->name);
+	        alg->u.kex.kex = k->list[j];
+		alg->u.kex.warn = warn;
 	    }
 	}
 	/* List server host key algorithms. */
         if (!s->got_session_id) {
             /*
              * In the first key exchange, we list all the algorithms
-             * we're prepared to cope with.
+             * we're prepared to cope with, but prefer those algorithms
+	     * for which we have a host key for this host.
              */
-	    n = 0;
             for (i = 0; i < lenof(hostkey_algs); i++) {
-	        assert(n < MAXKEXLIST);
-		s->kexlists[KEXLIST_HOSTKEY][n].name = hostkey_algs[i]->name;
-		s->kexlists[KEXLIST_HOSTKEY][n].u.hostkey = hostkey_algs[i];
-		n++;
+		if (have_ssh_host_key(ssh->savedhost, ssh->savedport,
+				      hostkey_algs[i]->keytype)) {
+		    alg = ssh2_kexinit_addalg(s->kexlists[KEXLIST_HOSTKEY],
+					      hostkey_algs[i]->name);
+		    alg->u.hostkey = hostkey_algs[i];
+		}
+	    }
+            for (i = 0; i < lenof(hostkey_algs); i++) {
+		alg = ssh2_kexinit_addalg(s->kexlists[KEXLIST_HOSTKEY],
+					  hostkey_algs[i]->name);
+		alg->u.hostkey = hostkey_algs[i];
 	    }
         } else {
             /*
@@ -6380,44 +6470,39 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
              * reverification.
              */
             assert(ssh->kex);
-	    s->kexlists[KEXLIST_HOSTKEY][0].name = ssh->hostkey->name;
-	    s->kexlists[KEXLIST_HOSTKEY][0].u.hostkey = ssh->hostkey;
+	    alg = ssh2_kexinit_addalg(s->kexlists[KEXLIST_HOSTKEY],
+				      ssh->hostkey->name);
+	    alg->u.hostkey = ssh->hostkey;
         }
 	/* List encryption algorithms (client->server then server->client). */
 	for (k = KEXLIST_CSCIPHER; k <= KEXLIST_SCCIPHER; k++) {
-	    n = 0;
 	    warn = FALSE;
 	    for (i = 0; i < s->n_preferred_ciphers; i++) {
 		const struct ssh2_ciphers *c = s->preferred_ciphers[i];
 		if (!c) warn = TRUE;
 		else for (j = 0; j < c->nciphers; j++) {
-		    assert(n < MAXKEXLIST);
-		    s->kexlists[k][n].name =  c->list[j]->name;
-		    s->kexlists[k][n].u.cipher.cipher = c->list[j];
-		    s->kexlists[k][n].u.cipher.warn = warn;
-		    n++;
+		    alg = ssh2_kexinit_addalg(s->kexlists[k],
+					      c->list[j]->name);
+		    alg->u.cipher.cipher = c->list[j];
+		    alg->u.cipher.warn = warn;
 		}
 	    }
 	}
 	/* List MAC algorithms (client->server then server->client). */
 	for (j = KEXLIST_CSMAC; j <= KEXLIST_SCMAC; j++) {
-	    n = 0;
 	    for (i = 0; i < s->nmacs; i++) {
-		assert(n < MAXKEXLIST);
-		s->kexlists[j][n].name =  s->maclist[i]->name;
-		s->kexlists[j][n].u.mac.mac = s->maclist[i];
-		s->kexlists[j][n].u.mac.etm = FALSE;
-		n++;
+		alg = ssh2_kexinit_addalg(s->kexlists[j], s->maclist[i]->name);
+		alg->u.mac.mac = s->maclist[i];
+		alg->u.mac.etm = FALSE;
             }
 	    for (i = 0; i < s->nmacs; i++)
                 /* For each MAC, there may also be an ETM version,
                  * which we list second. */
                 if (s->maclist[i]->etm_name) {
-		    assert(n < MAXKEXLIST);
-		    s->kexlists[j][n].name =  s->maclist[i]->etm_name;
-		    s->kexlists[j][n].u.mac.mac = s->maclist[i];
-		    s->kexlists[j][n].u.mac.etm = TRUE;
-		    n++;
+		    alg = ssh2_kexinit_addalg(s->kexlists[j],
+					      s->maclist[i]->etm_name);
+		    alg->u.mac.mac = s->maclist[i];
+		    alg->u.mac.etm = TRUE;
 		}
 	}
 	/* List client->server compression algorithms,
@@ -6426,26 +6511,23 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
 	for (j = KEXLIST_CSCOMP; j <= KEXLIST_SCCOMP; j++) {
 	    assert(lenof(compressions) > 1);
 	    /* Prefer non-delayed versions */
-	    s->kexlists[j][0].name = s->preferred_comp->name;
-	    s->kexlists[j][0].u.comp = s->preferred_comp;
+	    alg = ssh2_kexinit_addalg(s->kexlists[j], s->preferred_comp->name);
+	    alg->u.comp = s->preferred_comp;
 	    /* We don't even list delayed versions of algorithms until
 	     * they're allowed to be used, to avoid a race. See the end of
 	     * this function. */
-	    n = 1;
 	    if (s->userauth_succeeded && s->preferred_comp->delayed_name) {
-		s->kexlists[j][1].name = s->preferred_comp->delayed_name;
-		s->kexlists[j][1].u.comp = s->preferred_comp;
-		n = 2;
+		alg = ssh2_kexinit_addalg(s->kexlists[j],
+					  s->preferred_comp->delayed_name);
+		alg->u.comp = s->preferred_comp;
 	    }
 	    for (i = 0; i < lenof(compressions); i++) {
 		const struct ssh_compress *c = compressions[i];
-		s->kexlists[j][n].name = c->name;
-		s->kexlists[j][n].u.comp = c;
-		n++;
+		alg = ssh2_kexinit_addalg(s->kexlists[j], c->name);
+		alg->u.comp = c;
 		if (s->userauth_succeeded && c->delayed_name) {
-		    s->kexlists[j][n].name = c->delayed_name;
-		    s->kexlists[j][n].u.comp = c;
-		    n++;
+		    alg = ssh2_kexinit_addalg(s->kexlists[j], c->delayed_name);
+		    alg->u.comp = c;
 		}
 	    }
 	}
@@ -6512,6 +6594,24 @@ 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;
@@ -6556,6 +6656,7 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
 	    crStopV;
 	  matched:;
 	}
+
 	if (s->pending_compression) {
 	    logevent("Server supports delayed compression; "
 		     "will try this later");
@@ -6661,8 +6762,8 @@ 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->real_keybits;
+            scbits = s->sccipher_tobe->real_keybits;
             s->nbits = (csbits > scbits ? csbits : scbits);
         }
         /* The keys only have hlen-bit entropy, since they're based on
@@ -6739,6 +6840,10 @@ 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);
@@ -6747,6 +6852,10 @@ 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);
@@ -6782,7 +6891,8 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
         }
     } else if (ssh->kex->main_type == KEXTYPE_ECDH) {
 
-        logeventf(ssh, "Doing ECDH key exchange with hash %s",
+        logeventf(ssh, "Doing ECDH key exchange with curve %s and hash %s",
+                  ssh_ecdhkex_curve_textname(ssh->kex),
                   ssh->kex->hash->text_name);
         ssh->pkt_kctx = SSH2_PKTCTX_ECDHKEX;
 
@@ -6817,6 +6927,10 @@ 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);
@@ -6839,6 +6953,10 @@ 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) {
@@ -6849,6 +6967,10 @@ 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 {
@@ -6866,6 +6988,10 @@ 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,
@@ -6874,6 +7000,10 @@ 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);
         }
@@ -6950,6 +7080,10 @@ 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);
     }
@@ -7068,7 +7202,7 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
 	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_mac_ctx = ssh->csmac->make_context(ssh->cs_cipher_ctx);
 
     if (ssh->cs_comp_ctx)
 	ssh->cscomp->compress_cleanup(ssh->cs_comp_ctx);
@@ -7080,28 +7214,33 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
      * 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));
+	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);
+
+	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);
     }
 
     logeventf(ssh, "Initialised %.200s client->server encryption",
 	      ssh->cscipher->text_name);
-    logeventf(ssh, "Initialised %.200s client->server MAC algorithm%s",
+    logeventf(ssh, "Initialised %.200s client->server MAC algorithm%s%s",
 	      ssh->csmac->text_name,
-              ssh->csmac_etm ? " (in ETM mode)" : "");
+              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);
@@ -7136,7 +7275,7 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
 	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_mac_ctx = ssh->scmac->make_context(ssh->sc_cipher_ctx);
 
     if (ssh->sc_comp_ctx)
 	ssh->sccomp->decompress_cleanup(ssh->sc_comp_ctx);
@@ -7148,27 +7287,32 @@ static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
      * 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));
+	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);
+
+	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);
     }
     logeventf(ssh, "Initialised %.200s server->client encryption",
 	      ssh->sccipher->text_name);
-    logeventf(ssh, "Initialised %.200s server->client MAC algorithm%s",
+    logeventf(ssh, "Initialised %.200s server->client MAC algorithm%s%s",
 	      ssh->scmac->text_name,
-              ssh->scmac_etm ? " (in ETM mode)" : "");
+              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);
@@ -7743,7 +7887,7 @@ 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
@@ -7758,9 +7902,14 @@ static void ssh_check_termination(Ssh ssh)
     }
 }
 
-void ssh_sharing_downstream_connected(Ssh ssh, unsigned id)
+void ssh_sharing_downstream_connected(Ssh ssh, unsigned id,
+                                      const char *peerinfo)
 {
-    logeventf(ssh, "Connection sharing downstream #%u connected", id);
+    if (peerinfo)
+        logeventf(ssh, "Connection sharing downstream #%u connected from %s",
+                  id, peerinfo);
+    else
+        logeventf(ssh, "Connection sharing downstream #%u connected", id);
 }
 
 void ssh_sharing_downstream_disconnected(Ssh ssh, unsigned id)
@@ -9279,11 +9428,20 @@ 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
 	    }
 
@@ -10477,7 +10635,8 @@ 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);
 	}
     }
 
@@ -11501,6 +11660,7 @@ Backend ssh_backend = {
     ssh_provide_logctx,
     ssh_unthrottle,
     ssh_cfg_info,
+    ssh_test_for_upstream,
     "ssh",
     PROT_SSH,
     22