monitoring-plugins' check_dhcp has some weird in a counter: $ doas /usr/local/libexec/nagios/check_dhcp -s 10.17.11.55 -u -i bnx0 OK: Received 260350 DHCPOFFER(s), 1 of 1 requested servers responded, max lease time = 21600 sec.
This is caused by receive_dhcp_packet, which only does recvfrom(MSG_PEEK), which causes the packet to be found as long as the timer hasn't expired. The diff below removes the MSG_PEEK flag and returns the correct value: $ doas ./check_dhcp -s 10.17.11.55 -u -i trunk0 OK: Received 1 DHCPOFFER(s), 1 of 1 requested servers responded, max lease time = 21600 sec. OK? martijn@ Index: patches/patch-plugins-root_check_dhcp_c =================================================================== RCS file: /cvs/ports/net/monitoring-plugins/patches/patch-plugins-root_check_dhcp_c,v retrieving revision 1.1 diff -u -p -r1.1 patch-plugins-root_check_dhcp_c --- patches/patch-plugins-root_check_dhcp_c 19 Jul 2017 12:14:29 -0000 1.1 +++ patches/patch-plugins-root_check_dhcp_c 9 Jan 2019 16:00:36 -0000 @@ -3,8 +3,11 @@ Fix stack smashing. Upstream merge request: https://github.com/monitoring-plugins/monitoring-plugins/pull/1500 ---- plugins-root/check_dhcp.c.orig Wed Jul 19 12:53:55 2017 -+++ plugins-root/check_dhcp.c Wed Jul 19 13:46:40 2017 + +MSG_PEEK causes the packet to be counted multiple times. +Index: plugins-root/check_dhcp.c +--- plugins-root/check_dhcp.c.orig ++++ plugins-root/check_dhcp.c @@ -323,7 +323,8 @@ int get_hardware_address(int sock,char *interface_name #elif defined(__bsd__) /* King 2004 see ACKNOWLEDGEMENTS */ @@ -15,3 +18,12 @@ https://github.com/monitoring-plugins/mo char *buf; unsigned char *ptr; struct if_msghdr *ifm; +@@ -693,7 +694,7 @@ int receive_dhcp_packet(void *buffer, int buffer_size, + else{ + bzero(&source_address,sizeof(source_address)); + address_size=sizeof(source_address); +- recv_result=recvfrom(sock,(char *)buffer,buffer_size,MSG_PEEK,(struct sockaddr *)&source_address,&address_size); ++ recv_result=recvfrom(sock,(char *)buffer,buffer_size,0,(struct sockaddr *)&source_address,&address_size); + if(verbose) + printf("recv_result: %d\n",recv_result); +
