* tcp.c, tcp_in.c, tcp_out.c, tcp.h: Modify way the retransmission

timer is reset to fix bug#19434, with help from Oleg Tyshev.

src/core/tcp.c

@@ -500,11 +500,13 @@ tcp_slowtmr(void)
       ++pcb_remove;
       LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: max DATA retries reached\n"));
     } else {
+      /* Increase the retransmission timer if it is running */
+      if(pcb->rtime >= 0)
         ++pcb->rtime;
-      if (pcb->unacked != NULL && pcb->rtime >= pcb->rto) {
 
+      if (pcb->unacked != NULL && pcb->rtime >= pcb->rto) {
         /* Time for a retransmission. */
-        LWIP_DEBUGF(TCP_RTO_DEBUG, ("tcp_slowtmr: rtime %"U16_F" pcb->rto %"U16_F"\n",
+        LWIP_DEBUGF(TCP_RTO_DEBUG, ("tcp_slowtmr: rtime %"S16_F" pcb->rto %"S16_F"\n",
                                     pcb->rtime, pcb->rto));
 
         /* Double retransmission time-out unless we are trying to
@@ -512,6 +514,10 @@ tcp_slowtmr(void)
         if (pcb->state != SYN_SENT) {
           pcb->rto = ((pcb->sa >> 3) + pcb->sv) << tcp_backoff[pcb->nrtx];
         }
+
+        /* Reset the retransmission timer. */
+        pcb->rtime = 0;
+
         /* Reduce congestion window and ssthresh. */
         eff_wnd = LWIP_MIN(pcb->cwnd, pcb->snd_wnd);
         pcb->ssthresh = eff_wnd >> 1;
@@ -844,7 +850,7 @@ tcp_alloc(u8_t prio)
     pcb->rto = 3000 / TCP_SLOW_INTERVAL;
     pcb->sa = 0;
     pcb->sv = 3000 / TCP_SLOW_INTERVAL;
-    pcb->rtime = 0;
+    pcb->rtime = -1;
     pcb->cwnd = 1;
     iss = tcp_next_iss();
     pcb->snd_wl2 = iss;
@@ -994,6 +1000,10 @@ tcp_pcb_purge(struct tcp_pcb *pcb)
       LWIP_DEBUGF(TCP_DEBUG, ("tcp_pcb_purge: data left on ->ooseq\n"));
     }
 
+    /* Stop the retransmission timer as it will expect data on unacked
+       queue if it fires */
+    pcb->rtime = -1;
+
     tcp_segs_free(pcb->ooseq);
     pcb->ooseq = NULL;
 #endif /* TCP_QUEUE_OOSEQ */

src/core/tcp_in.c

@@ -504,6 +504,14 @@ tcp_process(struct tcp_pcb *pcb)
       LWIP_DEBUGF(TCP_QLEN_DEBUG, ("tcp_process: SYN-SENT --queuelen %"U16_F"\n", (u16_t)pcb->snd_queuelen));
       rseg = pcb->unacked;
       pcb->unacked = rseg->next;
+
+      /* If there's nothing left to acknowledge, stop the retransmit
+         timer, otherwise reset it to start again */
+      if(pcb->unacked == NULL)
+        pcb->rtime = -1;
+      else
+        pcb->rtime = 0;
+
       tcp_seg_free(rseg);
 
       /* Parse any options in the SYNACK. */
@@ -700,10 +708,7 @@ tcp_receive(struct tcp_pcb *pcb)
         LWIP_DEBUGF(TCP_FR_DEBUG, ("tcp_receive: dupack averted %"U32_F" %"U32_F"\n",
                                    pcb->snd_wl1 + pcb->snd_wnd, right_wnd_edge));
       }
-    } else
+    } else if (TCP_SEQ_BETWEEN(ackno, pcb->lastack+1, pcb->snd_max)){
-      /*if (TCP_SEQ_LT(pcb->lastack, ackno) &&
-        TCP_SEQ_LEQ(ackno, pcb->snd_max)) { */
-      if (TCP_SEQ_BETWEEN(ackno, pcb->lastack+1, pcb->snd_max)){
       /* We come here when the ACK acknowledges new data. */
       
       /* Reset the "IN Fast Retransmit" flag, since we are no longer
@@ -775,6 +780,14 @@ tcp_receive(struct tcp_pcb *pcb)
                       pcb->unsent != NULL);
         }
       }
+
+      /* If there's nothing left to acknowledge, stop the retransmit
+         timer, otherwise reset it to start again */
+      if(pcb->unacked == NULL)
+        pcb->rtime = -1;
+      else
+        pcb->rtime = 0;
+
       pcb->polltmr = 0;
     }
 

src/core/tcp_out.c

@@ -551,6 +551,8 @@ tcp_output_segment(struct tcp_seg *seg, struct tcp_pcb *pcb)
     ip_addr_set(&(pcb->local_ip), &(netif->ip_addr));
   }
 
+  /* Set retransmission timer running if it is not currently enabled */
+  if(pcb->rtime == -1)
     pcb->rtime = 0;
 
   if (pcb->rttest == 0) {
@@ -674,7 +676,6 @@ tcp_rexmit(struct tcp_pcb *pcb)
   /* Do the actual retransmission. */
   snmp_inc_tcpretranssegs();
   tcp_output(pcb);
-
 }
 
 

src/include/lwip/tcp.h

@@ -253,7 +253,7 @@ struct tcp_pcb {
   u8_t polltmr, pollinterval;
   
   /* Retransmission timer. */
-  u16_t rtime;
+  s16_t rtime;
   
   u16_t mss;   /* maximum segment size */
   
@@ -262,7 +262,7 @@ struct tcp_pcb {
   u32_t rtseq;  /* sequence number being timed */
   s16_t sa, sv; /* @todo document this */
 
-  u16_t rto;    /* retransmission time-out */
+  s16_t rto;    /* retransmission time-out */
   u8_t nrtx;    /* number of retransmissions */
 
   /* fast retransmit/recovery */