fix/hack xl2tpd flow control

[Landry Breuil]

Hi,

for a year or so i've had the following local patch to xl2tpd -without
it, as soon as there's a 'large' packet over ppp, xl2tpd drops the cnx,
while if this check is killed out its perfectly fine and sort of usable.

Reported upstream as https://github.com/xelerance/xl2tpd/issues/133 but
so far no real reaction from upstream.

What do xl2tpd users think about it ? Am i the only one using it with
npppd on the serverside (which i dont control..)

(Oh and im building with
MAKE_FLAGS=DFLAGS="-DDEBUG_HELLO -DDEBUG_CLOSE -DDEBUG_FLOW -DDEBUG_PAYLOAD 
-DDEBUG_CONTROL -DDEBUG_CONTROL_XMIT -DDEBUG_PPPD -DDEBUG_AAA -DDEBUG_FILE 
-DDEBUG_AUTH"
because i love debugging l2tp code)

Landry

Index: control.c
--- control.c.orig
+++ control.c
@@ -1500,10 +1500,11 @@ static inline int expand_payload (struct buffer *buf, 
                c->pSr=new_hdr->Ns;
        } */
 #ifdef DEBUG_PAYLOAD
-    l2tp_log (LOG_DEBUG, "%s: payload, cid = %d, Ns = %d, Nr = %d\n", 
__FUNCTION__,
-         c->cid, new_hdr->Ns, new_hdr->Nr);
+    l2tp_log (LOG_DEBUG, "%s: payload, cid = %d, Ns = %d, Nr = %d, expecting 
%d but not giving a fuck\n", __FUNCTION__,
+         c->cid, new_hdr->Ns, new_hdr->Nr, c->data_seq_num);
 #endif
-    if (new_hdr->Ns != c->data_seq_num)
+    if (0)
+//    if (new_hdr->Ns != c->data_seq_num)
     {
         /* RFC1982-esque comparison of serial numbers */
         if (((new_hdr->Ns < c->data_rec_seq_num) &&
@@ -1525,8 +1526,8 @@ static inline int expand_payload (struct buffer *buf, 
 #ifdef DEBUG_FLOW
             if (DEBUG)
                 l2tp_log (LOG_DEBUG,
-                     "%s: Oops, lost a packet or two (%d).  continuing...\n",
-                     __FUNCTION__, new_hdr->Ns);
+                     "%s: Oops, lost a packet or two (got %d, expected %d).  
continuing...\n",
+                     __FUNCTION__, new_hdr->Ns, c->data_rec_seq_num);
 #endif
             c->data_rec_seq_num = new_hdr->Ns;
         }
@@ -1535,8 +1536,8 @@ static inline int expand_payload (struct buffer *buf, 
 #ifdef DEBUG_FLOW
             if (DEBUG)
                 l2tp_log (LOG_DEBUG,
-                     "%s: Received out of order payload packet (%d)\n",
-                     __FUNCTION__, new_hdr->Ns);
+                     "%s: Received out of order payload packet (got %d, 
expected %d)\n",
+                     __FUNCTION__, new_hdr->Ns, c->data_rec_seq_num);
 #endif
             return -EINVAL;
         }