More cleanly handle 3-byte IPv4 addresses.

Make a union of the 4 bytes of the address and the address as a 32-bit
integer, and fill in the bytes differently based on whether it's an
interior or exterior route.  Rather than just casting a pointer to a
byte to a pointer to a 4-byte integer - which may not be safe, as the
byte array might not be properly aligned - just use the integer member
of the union.

Change-Id: Ic0e78a832cedb9a5a8d435a6c911409b17e41685
Reviewed-on: https://code.wireshark.org/review/8443
Reviewed-by: Guy Harris <guy@alum.mit.edu>

1 files changed, 26 insertions, 12 deletions

diff --git a/epan/dissectors/packet-igrp.c b/epan/dissectors/packet-igrp.c
index 28429f450d..9ff2bb449b 100644
--- a/epan/dissectors/packet-igrp.c
+++ b/epan/dissectors/packet-igrp.c
@@ -156,22 +156,36 @@ static void dissect_igrp(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
 
 static void dissect_vektor_igrp (tvbuff_t *tvb, proto_tree *igrp_vektor_tree, guint8 network)
 {
-  guint8 *ptr_addr,addr[5];
+  union {
+    guint8 addr_bytes[4];
+    guint32 addr_word;
+  } addr;
   address ip_addr;
 
-  addr[0]=network;
-  addr[1]=tvb_get_guint8(tvb,0);
-  addr[2]=tvb_get_guint8(tvb,1);
-  addr[3]=tvb_get_guint8(tvb,2);
-  addr[4]=0;
-
-  ptr_addr=addr;
-  if (network==0) ptr_addr=&addr[1];
-
-  SET_ADDRESS(&ip_addr, AT_IPv4, 4, ptr_addr);
+  if (network != 0) {
+    /*
+     * Interior route; network is the high-order byte, and the three
+     * bytes in the vector are the lower 3 bytes.
+     */
+    addr.addr_bytes[0]=network;
+    addr.addr_bytes[1]=tvb_get_guint8(tvb,0);
+    addr.addr_bytes[2]=tvb_get_guint8(tvb,1);
+    addr.addr_bytes[3]=tvb_get_guint8(tvb,2);
+  } else {
+    /*
+     * System or exterior route; the three bytes in the vector are
+     * the three high-order bytes, and the low-order byte is 0.   
+     */
+    addr.addr_bytes[0]=tvb_get_guint8(tvb,0);
+    addr.addr_bytes[1]=tvb_get_guint8(tvb,1);
+    addr.addr_bytes[2]=tvb_get_guint8(tvb,2);
+    addr.addr_bytes[3]=0;
+  }                                                
+  
+  SET_ADDRESS(&ip_addr, AT_IPv4, 4, &addr);
   igrp_vektor_tree = proto_tree_add_subtree_format(igrp_vektor_tree, tvb, 0 ,14,
                                                    ett_igrp_net, NULL, "Entry for network %s", address_to_str(wmem_packet_scope(), &ip_addr));
-  proto_tree_add_ipv4(igrp_vektor_tree, hf_igrp_network, tvb, 0, 3, *((guint32*)ptr_addr));
+  proto_tree_add_ipv4(igrp_vektor_tree, hf_igrp_network, tvb, 0, 3, addr.addr_word);
   proto_tree_add_item(igrp_vektor_tree, hf_igrp_delay, tvb, 3, 3, ENC_BIG_ENDIAN);
   proto_tree_add_item(igrp_vektor_tree, hf_igrp_bandwidth, tvb, 6, 3, ENC_BIG_ENDIAN);
   proto_tree_add_uint_format_value(igrp_vektor_tree, hf_igrp_mtu, tvb, 9, 2, tvb_get_ntohs(tvb,9), "%d  bytes", tvb_get_ntohs(tvb,9));