Implement zlib@openssh.com, using the rekey-after-userauth method suggested in

the wishlist entry.

[originally from svn r9120]
[this svn revision also touched putty-website,putty-wishlist]

ssh.c

@@ -544,7 +544,7 @@ static int ssh_comp_none_disable(void *handle)
     return 0;
 }
 const static struct ssh_compress ssh_comp_none = {
-    "none",
+    "none", NULL,
     ssh_comp_none_init, ssh_comp_none_cleanup, ssh_comp_none_block,
     ssh_comp_none_init, ssh_comp_none_cleanup, ssh_comp_none_block,
     ssh_comp_none_disable, NULL
@@ -5422,6 +5422,8 @@ static int do_ssh2_transport(Ssh ssh, void *vin, int inlen,
 	int n_preferred_ciphers;
 	const struct ssh2_ciphers *preferred_ciphers[CIPHER_MAX];
 	const struct ssh_compress *preferred_comp;
+	int userauth_succeeded;	    /* for delayed compression */
+	int pending_compression;
 	int got_session_id, activated_authconn;
 	struct Packet *pktout;
         int dlgret;
@@ -5437,6 +5439,8 @@ static int do_ssh2_transport(Ssh ssh, void *vin, int inlen,
     s->cscomp_tobe = s->sccomp_tobe = NULL;
 
     s->got_session_id = s->activated_authconn = FALSE;
+    s->userauth_succeeded = FALSE;
+    s->pending_compression = FALSE;
 
     /*
      * Be prepared to work around the buggy MAC problem.
@@ -5601,26 +5605,32 @@ static int do_ssh2_transport(Ssh ssh, void *vin, int inlen,
 	    if (i < s->nmacs - 1)
 		ssh2_pkt_addstring_str(s->pktout, ",");
 	}
-	/* List client->server compression algorithms. */
-	ssh2_pkt_addstring_start(s->pktout);
-	assert(lenof(compressions) > 1);
-	ssh2_pkt_addstring_str(s->pktout, s->preferred_comp->name);
-	for (i = 0; i < lenof(compressions); i++) {
-	    const struct ssh_compress *c = compressions[i];
-	    if (c != s->preferred_comp) {
+	/* List client->server compression algorithms,
+	 * then server->client compression algorithms. (We use the
+	 * same set twice.) */
+	for (j = 0; j < 2; j++) {
+	    ssh2_pkt_addstring_start(s->pktout);
+	    assert(lenof(compressions) > 1);
+	    /* Prefer non-delayed versions */
+	    ssh2_pkt_addstring_str(s->pktout, s->preferred_comp->name);
+	    /* 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. */
+	    if (s->userauth_succeeded && s->preferred_comp->delayed_name) {
 		ssh2_pkt_addstring_str(s->pktout, ",");
-		ssh2_pkt_addstring_str(s->pktout, c->name);
+		ssh2_pkt_addstring_str(s->pktout,
+				       s->preferred_comp->delayed_name);
 	    }
-	}
-	/* List server->client compression algorithms. */
-	ssh2_pkt_addstring_start(s->pktout);
-	assert(lenof(compressions) > 1);
-	ssh2_pkt_addstring_str(s->pktout, s->preferred_comp->name);
-	for (i = 0; i < lenof(compressions); i++) {
-	    const struct ssh_compress *c = compressions[i];
-	    if (c != s->preferred_comp) {
-		ssh2_pkt_addstring_str(s->pktout, ",");
-		ssh2_pkt_addstring_str(s->pktout, c->name);
+	    for (i = 0; i < lenof(compressions); i++) {
+		const struct ssh_compress *c = compressions[i];
+		if (c != s->preferred_comp) {
+		    ssh2_pkt_addstring_str(s->pktout, ",");
+		    ssh2_pkt_addstring_str(s->pktout, c->name);
+		    if (s->userauth_succeeded && c->delayed_name) {
+			ssh2_pkt_addstring_str(s->pktout, ",");
+			ssh2_pkt_addstring_str(s->pktout, c->delayed_name);
+		    }
+		}
 	    }
 	}
 	/* List client->server languages. Empty list. */
@@ -5769,6 +5779,13 @@ static int do_ssh2_transport(Ssh ssh, void *vin, int inlen,
 	    if (in_commasep_string(c->name, str, len)) {
 		s->cscomp_tobe = c;
 		break;
+	    } else if (in_commasep_string(c->delayed_name, str, len)) {
+		if (s->userauth_succeeded) {
+		    s->cscomp_tobe = c;
+		    break;
+		} else {
+		    s->pending_compression = TRUE;  /* try this later */
+		}
 	    }
 	}
 	ssh_pkt_getstring(pktin, &str, &len);  /* server->client compression */
@@ -5778,8 +5795,19 @@ static int do_ssh2_transport(Ssh ssh, void *vin, int inlen,
 	    if (in_commasep_string(c->name, str, len)) {
 		s->sccomp_tobe = c;
 		break;
+	    } else if (in_commasep_string(c->delayed_name, str, len)) {
+		if (s->userauth_succeeded) {
+		    s->sccomp_tobe = c;
+		    break;
+		} else {
+		    s->pending_compression = TRUE;  /* try this later */
+		}
 	    }
 	}
+	if (s->pending_compression) {
+	    logevent("Server supports delayed compression; "
+		     "will try this later");
+	}
 	ssh_pkt_getstring(pktin, &str, &len);  /* client->server language */
 	ssh_pkt_getstring(pktin, &str, &len);  /* server->client language */
 	s->ignorepkt = ssh2_pkt_getbool(pktin) && !s->guessok;
@@ -6315,19 +6343,52 @@ static int do_ssh2_transport(Ssh ssh, void *vin, int inlen,
      * start.
      * 
      * We _also_ go back to the start if we see pktin==NULL and
-     * inlen==-1, because this is a special signal meaning
+     * inlen negative, because this is a special signal meaning
      * `initiate client-driven rekey', and `in' contains a message
      * giving the reason for the rekey.
+     *
+     * inlen==-1 means always initiate a rekey;
+     * inlen==-2 means that userauth has completed successfully and
+     *   we should consider rekeying (for delayed compression).
      */
     while (!((pktin && pktin->type == SSH2_MSG_KEXINIT) ||
-	     (!pktin && inlen == -1))) {
+	     (!pktin && inlen < 0))) {
         wait_for_rekey:
 	crReturn(1);
     }
     if (pktin) {
 	logevent("Server initiated key re-exchange");
     } else {
+	if (inlen == -2) {
+	    /* 
+	     * authconn has seen a USERAUTH_SUCCEEDED. Time to enable
+	     * delayed compression, if it's available.
+	     *
+	     * draft-miller-secsh-compression-delayed-00 says that you
+	     * negotiate delayed compression in the first key exchange, and
+	     * both sides start compressing when the server has sent
+	     * USERAUTH_SUCCESS. This has a race condition -- the server
+	     * can't know when the client has seen it, and thus which incoming
+	     * packets it should treat as compressed.
+	     *
+	     * Instead, we do the initial key exchange without offering the
+	     * delayed methods, but note if the server offers them; when we
+	     * get here, if a delayed method was available that was higher
+	     * on our list than what we got, we initiate a rekey in which we
+	     * _do_ list the delayed methods (and hopefully get it as a
+	     * result). Subsequent rekeys will do the same.
+	     */
+	    assert(!s->userauth_succeeded); /* should only happen once */
+	    s->userauth_succeeded = TRUE;
+	    if (!s->pending_compression)
+		/* Can't see any point rekeying. */
+		goto wait_for_rekey;       /* this is utterly horrid */
+	    /* else fall through to rekey... */
+	    s->pending_compression = FALSE;
+	}
         /*
+	 * Now we've decided to rekey.
+	 *
          * Special case: if the server bug is set that doesn't
          * allow rekeying, we give a different log message and
          * continue waiting. (If such a server _initiates_ a rekey,
@@ -6345,7 +6406,7 @@ static int do_ssh2_transport(Ssh ssh, void *vin, int inlen,
                     schedule_timer(ssh->cfg.ssh_rekey_time*60*TICKSPERSEC,
                                    ssh2_timer, ssh);
             }
-            goto wait_for_rekey;       /* this is utterly horrid */
+            goto wait_for_rekey;       /* this is still utterly horrid */
         } else {
             logeventf(ssh, "Initiating key re-exchange (%s)", (char *)in);
         }
@@ -7256,7 +7317,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
 	int tried_gssapi;
 #endif
 	int kbd_inter_refused;
-	int we_are_in;
+	int we_are_in, userauth_success;
 	prompts_t *cur_prompt;
 	int num_prompts;
 	char username[100];
@@ -7292,7 +7353,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
     crBegin(ssh->do_ssh2_authconn_crstate);
 
     s->done_service_req = FALSE;
-    s->we_are_in = FALSE;
+    s->we_are_in = s->userauth_success = FALSE;
 #ifndef NO_GSSAPI
     s->tried_gssapi = FALSE;
 #endif
@@ -7582,7 +7643,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
 	    }
 	    if (pktin->type == SSH2_MSG_USERAUTH_SUCCESS) {
 		logevent("Access granted");
-		s->we_are_in = TRUE;
+		s->we_are_in = s->userauth_success = TRUE;
 		break;
 	    }
 
@@ -8590,6 +8651,20 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
     if (s->agent_response)
 	sfree(s->agent_response);
 
+    if (s->userauth_success) {
+	/*
+	 * We've just received USERAUTH_SUCCESS, and we haven't sent any
+	 * packets since. Signal the transport layer to consider enacting
+	 * delayed compression.
+	 *
+	 * (Relying on we_are_in is not sufficient, as
+	 * draft-miller-secsh-compression-delayed is quite clear that it
+	 * triggers on USERAUTH_SUCCESS specifically, and we_are_in can
+	 * become set for other reasons.)
+	 */
+	do_ssh2_transport(ssh, "enabling delayed compression", -2, NULL);
+    }
+
     /*
      * Now the connection protocol has started, one way or another.
      */

ssh.h

@@ -251,6 +251,9 @@ struct ssh_signkey {
 
 struct ssh_compress {
     char *name;
+    /* For zlib@openssh.com: if non-NULL, this name will be considered once
+     * userauth has completed successfully. */
+    char *delayed_name;
     void *(*compress_init) (void);
     void (*compress_cleanup) (void *);
     int (*compress) (void *, unsigned char *block, int len,

sshzlib.c

@@ -1371,6 +1371,7 @@ int main(int argc, char **argv)
 
 const struct ssh_compress ssh_zlib = {
     "zlib",
+    "zlib@openssh.com", /* delayed version */
     zlib_compress_init,
     zlib_compress_cleanup,
     zlib_compress_block,