From 8baf56acd60933f2fead38af0797a5fb2fdc06f2 Mon Sep 17 00:00:00 2001 From: florian Date: Sat, 6 Mar 2021 18:33:44 +0000 Subject: [PATCH] Turns out there are dhcp servers that ignore DHCPREQUEST messages when they don't like them instead of sending a DHCPNAK. Found the hard way by benno who didn't want to wait 127 seconds. Due to another bug dhcpleased would have exit through a fatal() in the frontend process if he had waited long enough for a Rebooting -> Init transition because we didn't deconfigure our IP address and thus didn't close our UDP socket. Upon configuring a new IP address we would open a new UDP socket send it to the frontend which would then fatal() due to an unexpected fd passed in. Aproporiate timings are rather underspecified in RFC 2131. Instead of doing an exponential backoff up to 64 in the "Rebooting" and "Requesting" state only go up to 2 for a total of 3 packets and total timeout of 3 seconds before going into "Init" state and sending a DHCPDISCOVER. To prevent the fatal() in the frontend process we reshuffle the state transition into the "Init" state and deconfigure the IP when appropriate. --- sbin/dhcpleased/engine.c | 40 ++++++++++++++++++++++++---------------- 1 file changed, 24 insertions(+), 16 deletions(-) diff --git a/sbin/dhcpleased/engine.c b/sbin/dhcpleased/engine.c index ce13e1c0cb4..b0e639ea264 100644 --- a/sbin/dhcpleased/engine.c +++ b/sbin/dhcpleased/engine.c @@ -1,4 +1,4 @@ -/* $OpenBSD: engine.c,v 1.6 2021/03/01 15:56:31 florian Exp $ */ +/* $OpenBSD: engine.c,v 1.7 2021/03/06 18:33:44 florian Exp $ */ /* * Copyright (c) 2017, 2021 Florian Obser @@ -56,7 +56,8 @@ * networks are faster these days. */ #define START_EXP_BACKOFF 1 -#define MAX_EXP_BACKOFF 64 /* RFC 2131 4.1 p23 */ +#define MAX_EXP_BACKOFF_SLOW 64 /* RFC 2131 4.1 p23 */ +#define MAX_EXP_BACKOFF_FAST 2 #define MINIMUM(a, b) (((a) < (b)) ? (a) : (b)) enum if_state { @@ -1025,9 +1026,6 @@ parse_dhcp(struct dhcpleased_iface *iface, struct imsg_dhcp *dhcp) return; } - /* we have been told that our IP is inapropriate, delete now */ - send_rdns_withdraw(iface); - send_deconfigure_interface(iface); state_transition(iface, IF_INIT); break; default: @@ -1075,21 +1073,31 @@ state_transition(struct dhcpleased_iface *iface, enum if_state new_state) } break; case IF_INIT: - if (old_state == IF_REBINDING) { - /* lease expired, delete IP */ + switch (old_state) { + case IF_INIT: + if (iface->timo.tv_sec < MAX_EXP_BACKOFF_SLOW) + iface->timo.tv_sec *= 2; + break; + case IF_REQUESTING: + case IF_RENEWING: + case IF_REBINDING: + case IF_REBOOTING: + /* lease expired, got DHCPNAK or timeout: delete IP */ send_rdns_withdraw(iface); send_deconfigure_interface(iface); - } - if (old_state == IF_INIT) { - if (iface->timo.tv_sec < MAX_EXP_BACKOFF) - iface->timo.tv_sec *= 2; - } else + /* fall through */ + case IF_DOWN: iface->timo.tv_sec = START_EXP_BACKOFF; + break; + case IF_BOUND: + fatal("invalid transition Bound -> Init"); + break; + } request_dhcp_discover(iface); break; case IF_REBOOTING: if (old_state == IF_REBOOTING) { - if (iface->timo.tv_sec < MAX_EXP_BACKOFF) + if (iface->timo.tv_sec < MAX_EXP_BACKOFF_FAST) iface->timo.tv_sec *= 2; } else { /* make sure we send broadcast */ @@ -1100,7 +1108,7 @@ state_transition(struct dhcpleased_iface *iface, enum if_state new_state) break; case IF_REQUESTING: if (old_state == IF_REQUESTING) { - if (iface->timo.tv_sec < MAX_EXP_BACKOFF) + if (iface->timo.tv_sec < MAX_EXP_BACKOFF_FAST) iface->timo.tv_sec *= 2; } else iface->timo.tv_sec = START_EXP_BACKOFF; @@ -1164,13 +1172,13 @@ iface_timeout(int fd, short events, void *arg) state_transition(iface, IF_INIT); break; case IF_REBOOTING: - if (iface->timo.tv_sec >= MAX_EXP_BACKOFF) + if (iface->timo.tv_sec >= MAX_EXP_BACKOFF_FAST) state_transition(iface, IF_INIT); else state_transition(iface, IF_REBOOTING); break; case IF_REQUESTING: - if (iface->timo.tv_sec >= MAX_EXP_BACKOFF) + if (iface->timo.tv_sec >= MAX_EXP_BACKOFF_FAST) state_transition(iface, IF_INIT); else state_transition(iface, IF_REQUESTING); -- 2.20.1