Apply TCP_EXPIRE_CONNECTED (86400 seconds) timeout only to established

connections, after SYN packets were seen from both ends.  Before this,
it would get applied right after the first SYN packet was seen (either
from client or server).  With broken TCP connection attempts, when the
remote end does not respond with SYNACK nor with RST, this resulted in
having a useless (ie, no actual TCP connection associated with it) TCP
link with 86400 seconds TTL, wasting system memory.  With high rate of
such broken connection attempts (for example, remote end simply blocks
these connection attempts with ipfw(8) without sending RST back), this
could result in a denial-of-service.

PR:		bin/17963

1 files changed, 10 insertions, 16 deletions

diff --git a/lib/libalias/alias_db.c b/lib/libalias/alias_db.c
index 86223cd..1ea3413 100644
--- a/lib/libalias/alias_db.c
+++ b/lib/libalias/alias_db.c
@@ -1544,22 +1544,19 @@ SetStateIn(struct alias_link *link, int state)
     /* TCP input state */
     switch (state) {
     case ALIAS_TCP_STATE_DISCONNECTED:
-        if (link->data.tcp->state.out != ALIAS_TCP_STATE_CONNECTED) {
+        if (link->data.tcp->state.out != ALIAS_TCP_STATE_CONNECTED)
             link->expire_time = TCP_EXPIRE_DEAD;
-        } else {
+        else
             link->expire_time = TCP_EXPIRE_SINGLEDEAD;
-        }
-        link->data.tcp->state.in = state;
         break;
     case ALIAS_TCP_STATE_CONNECTED:
-        link->expire_time = TCP_EXPIRE_CONNECTED;
-        /*FALLTHROUGH*/
-    case ALIAS_TCP_STATE_NOT_CONNECTED:
-        link->data.tcp->state.in = state;
+        if (link->data.tcp->state.out == ALIAS_TCP_STATE_CONNECTED)
+            link->expire_time = TCP_EXPIRE_CONNECTED;
         break;
     default:
         abort();
     }
+    link->data.tcp->state.in = state;
 }
 
 
@@ -1569,22 +1566,19 @@ SetStateOut(struct alias_link *link, int state)
     /* TCP output state */
     switch (state) {
     case ALIAS_TCP_STATE_DISCONNECTED:
-        if (link->data.tcp->state.in != ALIAS_TCP_STATE_CONNECTED) {
+        if (link->data.tcp->state.in != ALIAS_TCP_STATE_CONNECTED)
             link->expire_time = TCP_EXPIRE_DEAD;
-        } else {
+        else
             link->expire_time = TCP_EXPIRE_SINGLEDEAD;
-        }
-        link->data.tcp->state.out = state;
         break;
     case ALIAS_TCP_STATE_CONNECTED:
-        link->expire_time = TCP_EXPIRE_CONNECTED;
-        /*FALLTHROUGH*/
-    case ALIAS_TCP_STATE_NOT_CONNECTED:
-        link->data.tcp->state.out = state;
+        if (link->data.tcp->state.in == ALIAS_TCP_STATE_CONNECTED)
+            link->expire_time = TCP_EXPIRE_CONNECTED;
         break;
     default:
         abort();
     }
+    link->data.tcp->state.out = state;
 }