Fix up UDP length calculations. Fix checksum algorithm.

diff --git a/common/packet.c b/common/packet.c
index f354100ecc6e6ad3cf3897ea8856115a6cec7710..ff76bbb59d4bdb808b0684cccb9f580459be707a 100644 (file)
--- a/common/packet.c
+++ b/common/packet.c
@@ -22,7 +22,7 @@
 
 #ifndef lint
 static char copyright[] =
-"$Id: packet.c,v 1.24 1999/04/12 21:37:03 mellon Exp $ Copyright (c) 1996 The Internet Software Consortium.  All rights reserved.\n";
+"$Id: packet.c,v 1.25 1999/04/23 15:38:57 mellon Exp $ Copyright (c) 1996 The Internet Software Consortium.  All rights reserved.\n";
 #endif /* not lint */
 
 #include "dhcpd.h"
@@ -52,6 +52,9 @@ u_int32_t checksum (buf, nbytes, sum)
                log_debug ("sum = %x", sum);
 #endif
                sum += (u_int16_t) ntohs(*((u_int16_t *)(buf + i)));
+               /* Add carry. */
+               if (sum > 0xFFFF)
+                       sum -= 0xFFFF;
        }       
 
        /* If there's a single byte left over, checksum it, too.   Network
@@ -61,13 +64,15 @@ u_int32_t checksum (buf, nbytes, sum)
                log_debug ("sum = %x", sum);
 #endif
                sum += buf [i] << 8;
+               /* Add carry. */
+               if (sum > 0xFFFF)
+                       sum -= 0xFFFF;
        }
        
        return sum;
 }
 
-/* Fold the upper sixteen bits of the checksum down into the lower bits,
-   complement the sum, and then put it into network byte order. */
+/* Finish computing the checksum, and then put it into network byte order. */
 
 u_int32_t wrapsum (sum)
        u_int32_t sum;
@@ -76,17 +81,7 @@ u_int32_t wrapsum (sum)
        log_debug ("wrapsum (%x)", sum);
 #endif
 
-       while (sum > 0x10000) {
-               sum = (sum >> 16) + (sum & 0xFFFF);
-#ifdef DEBUG_CHECKSUM_VERBOSE
-               log_debug ("sum = %x", sum);
-#endif
-               sum += (sum >> 16);
-#ifdef DEBUG_CHECKSUM_VERBOSE
-               log_debug ("sum = %x", sum);
-#endif
-       }
-       sum = sum ^ 0xFFFF;
+       sum = ~sum & 0xFFFF;
 #ifdef DEBUG_CHECKSUM_VERBOSE
        log_debug ("sum = %x", sum);
 #endif
@@ -250,12 +245,12 @@ ssize_t decode_udp_ip_header (interface, buf, bufix, from, data, buflen)
          return -1;
 #endif /* USERLAND_FILTER */
 
-  ++ip_packets_seen;
   /* Check the IP header checksum - it should be zero. */
+  ++ip_packets_seen;
   if (wrapsum (checksum (buf + bufix, ip_len, 0))) {
          ++ip_packets_bad_checksum;
          if (ip_packets_seen > 4 &&
-             (++ip_packets_seen / ++ip_packets_bad_checksum) < 2) {
+             (ip_packets_seen / ip_packets_bad_checksum) < 2) {
                  log_info ("%d bad IP checksums seen in %d packets",
                            ip_packets_bad_checksum, ip_packets_seen);
                  ip_packets_seen = ip_packets_bad_checksum = 0;
@@ -279,7 +274,7 @@ ssize_t decode_udp_ip_header (interface, buf, bufix, from, data, buflen)
          data = buf + bufix + ip_len + sizeof *udp;
          len = ntohs (udp -> uh_ulen) - sizeof *udp;
          ++udp_packets_length_checked;
-         if (len + data > buf + buflen) {
+         if (len + data > buf + bufix + buflen) {
                  ++udp_packets_length_overflow;
                  if (udp_packets_length_checked > 4 &&
                      (udp_packets_length_checked /
@@ -287,8 +282,8 @@ ssize_t decode_udp_ip_header (interface, buf, bufix, from, data, buflen)
                          log_info ("%d udp packets in %d too long - dropped",
                                    udp_packets_length_overflow,
                                    udp_packets_length_checked);
-                         udp_packets_length_overflow
-                                 = udp_packets_length_checked = 0;
+                         udp_packets_length_overflow =
+                                 udp_packets_length_checked = 0;
                  }
                  return -1;
          }
@@ -310,10 +305,10 @@ ssize_t decode_udp_ip_header (interface, buf, bufix, from, data, buflen)
 
   ++udp_packets_seen;
   if (usum && usum != sum) {
-         ++udp_packets_bad_checksum;
+         udp_packets_bad_checksum++;
          if (udp_packets_seen > 4 &&
              (udp_packets_seen / udp_packets_bad_checksum) < 2) {
-                 log_info ("%d bad udp checksums seen in %d packets",
+                 log_info ("%d bad udp checksums in %d packets",
                            udp_packets_bad_checksum, udp_packets_seen);
                  udp_packets_seen = udp_packets_bad_checksum = 0;
          }