slirp: Implement TFTP Blocksize option

This option is described in RFC 1783. As this is only an optional field,
we may ignore it in some situations and handle it in some others.

However, MS Windows 2003 PXE boot client requests a block size of the MTU
(most of the times 1472 bytes), and doesn't work if the option is not
acknowledged (with whatever value).

According to the RFC 1783, we cannot acknowledge the option with a bigger
value than the requested one.

As current implementation is using 512 bytes by block, accept the option
with a value of 512 if the option was specified, and don't acknowledge it
if it is not present or less than 512 bytes.

Signed-off-by: Hervé Poussineau <hpoussin@reactos.org>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
(cherry picked from commit 95b1ad7ad86793c27ab8e9987be69571937900d1)

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

slirp/tftp.c

@@ -120,13 +120,13 @@ static int tftp_read_data(struct tftp_session *spt, uint32_t block_nr,
 }
 
 static int tftp_send_oack(struct tftp_session *spt,
-                          const char *key, uint32_t value,
+                          const char *keys[], uint32_t values[], int nb,
                           struct tftp_t *recv_tp)
 {
     struct sockaddr_in saddr, daddr;
     struct mbuf *m;
     struct tftp_t *tp;
-    int n = 0;
+    int i, n = 0;
 
     m = m_get(spt->slirp);
 
@@ -140,10 +140,12 @@ static int tftp_send_oack(struct tftp_session *spt,
     m->m_data += sizeof(struct udpiphdr);
 
     tp->tp_op = htons(TFTP_OACK);
-    n += snprintf(tp->x.tp_buf + n, sizeof(tp->x.tp_buf) - n, "%s",
-                  key) + 1;
-    n += snprintf(tp->x.tp_buf + n, sizeof(tp->x.tp_buf) - n, "%u",
-                  value) + 1;
+    for (i = 0; i < nb; i++) {
+        n += snprintf(tp->x.tp_buf + n, sizeof(tp->x.tp_buf) - n, "%s",
+                      keys[i]) + 1;
+        n += snprintf(tp->x.tp_buf + n, sizeof(tp->x.tp_buf) - n, "%u",
+                      values[i]) + 1;
+    }
 
     saddr.sin_addr = recv_tp->ip.ip_dst;
     saddr.sin_port = recv_tp->udp.uh_dport;
@@ -260,6 +262,9 @@ static void tftp_handle_rrq(Slirp *slirp, struct tftp_t *tp, int pktlen)
   int s, k;
   size_t prefix_len;
   char *req_fname;
+  const char *option_name[2];
+  uint32_t option_value[2];
+  int nb_options = 0;
 
   /* check if a session already exists and if so terminate it */
   s = tftp_session_find(slirp, tp);
@@ -337,7 +342,7 @@ static void tftp_handle_rrq(Slirp *slirp, struct tftp_t *tp, int pktlen)
       return;
   }
 
-  while (k < pktlen) {
+  while (k < pktlen && nb_options < ARRAY_SIZE(option_name)) {
       const char *key, *value;
 
       key = &tp->x.tp_buf[k];
@@ -364,11 +369,30 @@ static void tftp_handle_rrq(Slirp *slirp, struct tftp_t *tp, int pktlen)
 	      }
 	  }
 
-	  tftp_send_oack(spt, "tsize", tsize, tp);
-	  return;
+          option_name[nb_options] = "tsize";
+          option_value[nb_options] = tsize;
+          nb_options++;
+      } else if (strcasecmp(key, "blksize") == 0) {
+          int blksize = atoi(value);
+
+          /* If blksize option is bigger than what we will
+           * emit, accept the option with our packet size.
+           * Otherwise, simply do as we didn't see the option.
+           */
+          if (blksize >= 512) {
+              option_name[nb_options] = "blksize";
+              option_value[nb_options] = 512;
+              nb_options++;
+          }
       }
   }
 
+  if (nb_options > 0) {
+      assert(nb_options <= ARRAY_SIZE(option_name));
+      tftp_send_oack(spt, option_name, option_value, nb_options, tp);
+      return;
+  }
+
   spt->block_nr = 0;
   tftp_send_next_block(spt, tp);
 }