slirp: Handle more than 65535 blocks in TFTP transfers

RFC 1350 does not mention block count roll-over. However, a lot of TFTP servers
implement it to be able to transmit big files, so do it also.

Current block size is 512 bytes, so TFTP files were limited to 32 MB.

Signed-off-by: Hervé Poussineau <hpoussin@reactos.org>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
(cherry picked from commit 4aa401f39e048e71020cceb59f126ab941095a42)

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

slirp/tftp.c

@@ -97,7 +97,7 @@ static int tftp_session_find(Slirp *slirp, struct tftp_t *tp)
   return -1;
 }
 
-static int tftp_read_data(struct tftp_session *spt, uint16_t block_nr,
+static int tftp_read_data(struct tftp_session *spt, uint32_t block_nr,
                           uint8_t *buf, int len)
 {
     int bytes_read = 0;
@@ -197,19 +197,14 @@ out:
   tftp_session_terminate(spt);
 }
 
-static int tftp_send_data(struct tftp_session *spt,
-                          uint16_t block_nr,
-			  struct tftp_t *recv_tp)
+static int tftp_send_next_block(struct tftp_session *spt,
+                                struct tftp_t *recv_tp)
 {
   struct sockaddr_in saddr, daddr;
   struct mbuf *m;
   struct tftp_t *tp;
   int nobytes;
 
-  if (block_nr < 1) {
-    return -1;
-  }
-
   m = m_get(spt->slirp);
 
   if (!m) {
@@ -223,7 +218,7 @@ static int tftp_send_data(struct tftp_session *spt,
   m->m_data += sizeof(struct udpiphdr);
 
   tp->tp_op = htons(TFTP_DATA);
-  tp->x.tp_data.tp_block_nr = htons(block_nr);
+  tp->x.tp_data.tp_block_nr = htons((spt->block_nr + 1) & 0xffff);
 
   saddr.sin_addr = recv_tp->ip.ip_dst;
   saddr.sin_port = recv_tp->udp.uh_dport;
@@ -231,7 +226,7 @@ static int tftp_send_data(struct tftp_session *spt,
   daddr.sin_addr = spt->client_ip;
   daddr.sin_port = spt->client_port;
 
-  nobytes = tftp_read_data(spt, block_nr - 1, tp->x.tp_data.tp_buf, 512);
+  nobytes = tftp_read_data(spt, spt->block_nr, tp->x.tp_data.tp_buf, 512);
 
   if (nobytes < 0) {
     m_free(m);
@@ -255,6 +250,7 @@ static int tftp_send_data(struct tftp_session *spt,
     tftp_session_terminate(spt);
   }
 
+  spt->block_nr++;
   return 0;
 }
 
@@ -373,7 +369,8 @@ static void tftp_handle_rrq(Slirp *slirp, struct tftp_t *tp, int pktlen)
       }
   }
 
-  tftp_send_data(spt, 1, tp);
+  spt->block_nr = 0;
+  tftp_send_next_block(spt, tp);
 }
 
 static void tftp_handle_ack(Slirp *slirp, struct tftp_t *tp, int pktlen)
@@ -386,9 +383,8 @@ static void tftp_handle_ack(Slirp *slirp, struct tftp_t *tp, int pktlen)
     return;
   }
 
-  if (tftp_send_data(&slirp->tftp_sessions[s],
-		     ntohs(tp->x.tp_data.tp_block_nr) + 1,
-		     tp) < 0) {
+  if (tftp_send_next_block(&slirp->tftp_sessions[s],
+                           tp) < 0) {
     return;
   }
 }

slirp/tftp.h

@@ -37,6 +37,7 @@ struct tftp_session {
 
     struct in_addr client_ip;
     uint16_t client_port;
+    uint32_t block_nr;
 
     int timestamp;
 };