From: Guus Sliepen <guus@tinc-vpn.org>
Date: Sat, 27 May 2000 19:04:12 +0000 (+0000)
Subject: Fix for a DoS attack:
X-Git-Tag: release-1.0pre2~23
X-Git-Url: https://tinc-vpn.org/git/browse?p=tinc;a=commitdiff_plain;h=e4ff969a9868ecc25a85daab620f97227de8d493

Fix for a DoS attack:
 A remote user could telnet to the tinc daemon and type only this line:
 61 6 00000000/00000000:28f
 This would deny any packets to be sent to other tinc networks (except
 for to the hosts that run tincd's themselves). Solution is to skip
 hosts in lookup_conn() that have not been activated yet.
Fixed potential conn_list table corruption:
 If a new connection is accepted but a connection with the same subnet
 would already exist in the connection list, the OLD connection is
 terminated.
---

diff --git a/src/net.c b/src/net.c
index f8c7306d..2d16ae83 100644
--- a/src/net.c
+++ b/src/net.c
@@ -821,8 +821,8 @@ cp
 
   if(cl->status.outgoing)
     {
-      alarm(5);
       signal(SIGALRM, sigalrm_handler);
+      alarm(5);
       syslog(LOG_NOTICE, "Try to re-establish outgoing connection in 5 seconds.");
     }
   
diff --git a/src/netutl.c b/src/netutl.c
index cc8266d7..5b4badfd 100644
--- a/src/netutl.c
+++ b/src/netutl.c
@@ -37,7 +37,8 @@
 
 /*
   look for a connection associated with the given vpn ip,
-  return its connection structure
+  return its connection structure.
+  Skips connections that are not activated!
 */
 conn_list_t *lookup_conn(ip_t ip)
 {
@@ -45,10 +46,10 @@ conn_list_t *lookup_conn(ip_t ip)
 cp
   /* Exact match suggested by James B. MacLean */
   for(p = conn_list; p != NULL; p = p->next)
-    if(ip  == p->vpn_ip)
+    if((ip  == p->vpn_ip) && p->active)
       return p;
   for(p = conn_list; p != NULL; p = p->next)
-    if((ip & p->vpn_mask) == (p->vpn_ip & p->vpn_mask))
+    if(((ip & p->vpn_mask) == (p->vpn_ip & p->vpn_mask)) && p->active)
       return p;
 cp
   return NULL;
diff --git a/src/protocol.c b/src/protocol.c
index 3b81d7a2..3b23c9e2 100644
--- a/src/protocol.c
+++ b/src/protocol.c
@@ -188,7 +188,7 @@ void send_key_changed_all(void)
   conn_list_t *p;
 cp
   for(p = conn_list; p != NULL; p = p->next)
-    if(p->status.meta && p->protocol_version > PROT_3)
+    if(p->status.meta && p->active)
       send_key_changed(p, myself);
 cp
 }
@@ -332,7 +332,7 @@ int notify_others(conn_list_t *new, conn_list_t *source,
   conn_list_t *p;
 cp
   for(p = conn_list; p != NULL; p = p->next)
-    if(p != new && p != source && p->status.meta)
+    if(p != new && p != source && p->status.meta && p->active)
       function(p, new);
 cp
   return 0;
@@ -347,7 +347,7 @@ int notify_one(conn_list_t *new)
   conn_list_t *p;
 cp
   for(p = conn_list; p != NULL; p = p->next)
-    if(p != new && p->protocol_version > PROT_3)
+    if(p != new && p->active)
       send_add_host(new, p);
 cp
   return 0;
@@ -392,8 +392,6 @@ cp
 	return -1;
       send_passphrase(cl);
     }
-
-  cl->status.active = 0;
 cp
   return 0;
 }
@@ -424,6 +422,7 @@ cp
 int public_key_h(conn_list_t *cl)
 {
   char *g_n;
+  conn_list_t *old;
 cp
   if(sscanf(cl->buffer, "%*d %as", &g_n) != 1)
     {
@@ -449,6 +448,14 @@ cp
   else
     send_ack(cl);
 
+  /* Okay, before we active the connection, we check if there is another entry
+     in the connection list with the same vpn_ip. If so, it presumably is an
+     old connection that has timed out but we don't know it yet. Because our
+     conn_list entry is not active, lookup_conn will skip ourself. */
+
+  if(old=lookup_conn(cl->vpn_ip)) 
+    terminate_connection(old);
+
   cl->status.active = 1;
   notify_others(cl, NULL, send_add_host);
   notify_one(cl);