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Code Issues Releases Wiki Activity

Fix up UDP length calculations. Fix checksum algorithm.

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This commit is contained in:
Ted Lemon 1999-04-23 15:38:57 +00:00
parent 6177564f37
commit dda42ca14e
1 changed files with 16 additions and 21 deletions
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37
common/packet.c
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@ -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;
}