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Avoid a divide-by-zero when bad checksum counters overflow.

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A mixture of IP or UDP packets with valid and invalid checksum could
cause {ip,udp}_packets_bad_checksum to wrap around to 0, resulting
in a division by zero.

This is packet.c rev. 1.27 from OpenBSD.

admbugs:	552
Obtained from:	OpenBSD
MFC after:	3 days
This commit is contained in:
Mark Johnston 2019-06-26 20:11:52 +00:00
parent b66ed8ee28
commit a3ae40c7a4
1 changed files with 2 additions and 2 deletions
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4
sbin/dhclient/packet.c
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@ -183,7 +183,7 @@ decode_udp_ip_header(unsigned char *buf, int bufix, struct sockaddr_in *from,
ip_packets_seen++; ip_packets_seen++;
if (wrapsum(checksum(buf + bufix, ip_len, 0)) != 0) { if (wrapsum(checksum(buf + bufix, ip_len, 0)) != 0) {
ip_packets_bad_checksum++; ip_packets_bad_checksum++;
if (ip_packets_seen > 4 && if (ip_packets_seen > 4 && ip_packets_bad_checksum != 0 &&
(ip_packets_seen / ip_packets_bad_checksum) < 2) { (ip_packets_seen / ip_packets_bad_checksum) < 2) {
note("%d bad IP checksums seen in %d packets", note("%d bad IP checksums seen in %d packets",
ip_packets_bad_checksum, ip_packets_seen); ip_packets_bad_checksum, ip_packets_seen);
@ -235,7 +235,7 @@ decode_udp_ip_header(unsigned char *buf, int bufix, struct sockaddr_in *from,
udp_packets_seen++; udp_packets_seen++;
if (usum && usum != sum) { if (usum && usum != sum) {
udp_packets_bad_checksum++; udp_packets_bad_checksum++;
if (udp_packets_seen > 4 && if (udp_packets_seen > 4 && udp_packets_bad_checksum != 0 &&
(udp_packets_seen / udp_packets_bad_checksum) < 2) { (udp_packets_seen / udp_packets_bad_checksum) < 2) {
note("%d bad udp checksums in %d packets", note("%d bad udp checksums in %d packets",
udp_packets_bad_checksum, udp_packets_seen); udp_packets_bad_checksum, udp_packets_seen);