Support reconfiguration of key exchange in mid-session. The fiddly

bit is working out when to reschedule the next rekey for when the
timeout or data limit changes; sometimes it will be _right now_
because we're already over the new limit.

Still to do: the Kex panel should not appear in mid-session if we
are using SSHv1.

[originally from svn r5031]

config.c

@@ -1576,37 +1576,39 @@ void setup_config_box(struct controlbox *b, struct sesslist *sesslist,
 			  HELPCTX(ssh_ciphers),
 			  dlg_stdcheckbox_handler,
 			  I(offsetof(Config,ssh2_des_cbc)));
+	}
 
-	    /*
-	     * The Connection/SSH/Kex panel.
-	     */
-	    ctrl_settitle(b, "Connection/SSH/Kex",
-			  "Options controlling SSH key exchange");
+	/*
+	 * The Connection/SSH/Kex panel. (Owing to repeat key
+	 * exchange, this is all meaningful in mid-session.)
+	 */
+	ctrl_settitle(b, "Connection/SSH/Kex",
+		      "Options controlling SSH key exchange");
 
-	    s = ctrl_getset(b, "Connection/SSH/Kex", "main",
-			    "Key exchange algorithm options");
-	    c = ctrl_draglist(s, "Algorithm selection policy", 's',
-			      HELPCTX(ssh_kexlist),
-			      kexlist_handler, P(NULL));
-	    c->listbox.height = 5;
+	s = ctrl_getset(b, "Connection/SSH/Kex", "main",
+			"Key exchange algorithm options");
+	c = ctrl_draglist(s, "Algorithm selection policy", 's',
+			  HELPCTX(ssh_kexlist),
+			  kexlist_handler, P(NULL));
+	c->listbox.height = 5;
 
-	    s = ctrl_getset(b, "Connection/SSH/Kex", "repeat",
-			    "Options controlling key re-exchange");
+	s = ctrl_getset(b, "Connection/SSH/Kex", "repeat",
+			"Options controlling key re-exchange");
 
-	    /* FIXME: these could usefully be configured mid-session in SSH-2.
-	     *        (So could cipher/compression/kex, now we have rekey.) */
-	    ctrl_editbox(s, "Max minutes before rekey (0 for no limit)", 't', 20,
-			 HELPCTX(ssh_kex_repeat),
-			 dlg_stdeditbox_handler,
-			 I(offsetof(Config,ssh_rekey_time)),
-			 I(-1));
-	    ctrl_editbox(s, "Max data before rekey (0 for no limit)", 'd', 20,
-			 HELPCTX(ssh_kex_repeat),
-			 dlg_stdeditbox_handler,
-			 I(offsetof(Config,ssh_rekey_data)),
-			 I(16));
-	    ctrl_text(s, "(Use 1M for 1 megabyte, 1G for 1 gigabyte etc)",
-		      HELPCTX(ssh_kex_repeat));
+	ctrl_editbox(s, "Max minutes before rekey (0 for no limit)", 't', 20,
+		     HELPCTX(ssh_kex_repeat),
+		     dlg_stdeditbox_handler,
+		     I(offsetof(Config,ssh_rekey_time)),
+		     I(-1));
+	ctrl_editbox(s, "Max data before rekey (0 for no limit)", 'd', 20,
+		     HELPCTX(ssh_kex_repeat),
+		     dlg_stdeditbox_handler,
+		     I(offsetof(Config,ssh_rekey_data)),
+		     I(16));
+	ctrl_text(s, "(Use 1M for 1 megabyte, 1G for 1 gigabyte etc)",
+		  HELPCTX(ssh_kex_repeat));
+
+	if (!midsession) {
 
 	    /*
 	     * The Connection/SSH/Auth panel.

ssh.c

@@ -746,7 +746,7 @@ struct ssh_tag {
     unsigned long incoming_data_size, outgoing_data_size, deferred_data_size;
     unsigned long max_data_size;
     int kex_in_progress;
-    long next_rekey;
+    long next_rekey, last_rekey;
 };
 
 #define logevent(s) logevent(ssh->frontend, s)
@@ -5211,6 +5211,7 @@ static int do_ssh2_transport(Ssh ssh, unsigned char *in, int inlen,
      * Key exchange is over. Schedule a timer for our next rekey.
      */
     ssh->kex_in_progress = FALSE;
+    ssh->last_rekey = GETTICKCOUNT();
     if (ssh->cfg.ssh_rekey_time != 0)
 	ssh->next_rekey = schedule_timer(ssh->cfg.ssh_rekey_time*60*TICKSPERSEC,
 					 ssh2_timer, ssh);
@@ -7213,7 +7214,7 @@ static void ssh2_timer(void *ctx, long now)
 {
     Ssh ssh = (Ssh)ctx;
 
-    if (!ssh->kex_in_progress &&
+    if (!ssh->kex_in_progress && ssh->cfg.ssh_rekey_time != 0 &&
 	now - ssh->next_rekey >= 0) {
 	do_ssh2_transport(ssh, "Initiating key re-exchange (timeout)",
 			  -1, NULL);
@@ -7459,8 +7460,37 @@ static void ssh_free(void *handle)
 static void ssh_reconfig(void *handle, Config *cfg)
 {
     Ssh ssh = (Ssh) handle;
+    char *rekeying = NULL;
+    unsigned long old_max_data_size;
+
     pinger_reconfig(ssh->pinger, &ssh->cfg, cfg);
     ssh_setup_portfwd(ssh, cfg);
+
+    if (ssh->cfg.ssh_rekey_time != cfg->ssh_rekey_time &&
+	cfg->ssh_rekey_time != 0) {
+	long new_next = ssh->last_rekey + cfg->ssh_rekey_time*60*TICKSPERSEC;
+	long now = GETTICKCOUNT();
+
+	if (new_next - now < 0) {
+	    rekeying = "Initiating key re-exchange (timeout shortened)";
+	} else {
+	    ssh->next_rekey = schedule_timer(new_next - now, ssh2_timer, ssh);
+	}
+    }
+
+    old_max_data_size = ssh->max_data_size;
+    ssh->max_data_size = parse_blocksize(cfg->ssh_rekey_data);
+    if (old_max_data_size != ssh->max_data_size &&
+	ssh->max_data_size != 0) {
+	if (ssh->outgoing_data_size > ssh->max_data_size ||
+	    ssh->incoming_data_size > ssh->max_data_size)
+	    rekeying = "Initiating key re-exchange (data limit lowered)";
+    }
+
+    if (rekeying && !ssh->kex_in_progress) {
+	do_ssh2_transport(ssh, rekeying, -1, NULL);
+    }
+
     ssh->cfg = *cfg;		       /* STRUCTURE COPY */
 }