dhcpcd-discuss

Hi,

today a customer had a problem with a stray dhcp server in his net. I tried to 
get the IP of the server by sending a requesting with dhcpcd, but the ip of 
the offender wasn't written out by dhcpcd as it is usually done.

I found out that the server didn't set DHO_SERVERID.

So I added some code to dhcpcd to print out the source ip of the dhcp udp 
packet if the DHO_SERVERID option isn't set. Patch attached, please consider 
applying.

Kind regards,

Gerd

-- 
Address (better: trap) for people I really don't want to get mail from:
jonas@xxxxxxxxxxxxxxxxx

From 66985ab12e6cc7a9dc162906aea1cb7dcd09a991 Mon Sep 17 00:00:00 2001
From: Gerd von Egidy <gerd.von.egidy@xxxxxxxxxxxxx>
Date: Wed, 28 Apr 2010 12:02:17 +0200
Subject: [PATCH] improve log_dhcp to always tell from which server a message came

currently this information is derived from the DHO_SERVERID option.
But when the server doesn't set it, no source info is logged. Print
the src ip of the udp packet as "from" in this case. This is not perfect
as there could be a dhcp forwarder involved, but this is better than nothing.
---
 dhcpcd.c |   24 ++++++++++++------------
 1 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/dhcpcd.c b/dhcpcd.c
index 983c3b6..bc23934 100644
--- a/dhcpcd.c
+++ b/dhcpcd.c
@@ -407,7 +407,7 @@ start_expire(void *arg)
 
 static void
 log_dhcp(int lvl, const char *msg,
-    const struct interface *iface, const struct dhcp_message *dhcp)
+    const struct interface *iface, const struct dhcp_message *dhcp, const struct in_addr *from)
 {
 	char *a;
 	struct in_addr addr;
@@ -432,9 +432,9 @@ log_dhcp(int lvl, const char *msg,
 			syslog(lvl, "%s: %s %s from %s",
 			    iface->name, msg, a, inet_ntoa(addr));
 	} else if (a != NULL)
-		syslog(lvl, "%s: %s %s", iface->name, msg, a);
+		syslog(lvl, "%s: %s %s from %s", iface->name, msg, a, inet_ntoa(*from));
 	else
-		syslog(lvl, "%s: %s", iface->name, msg);
+		syslog(lvl, "%s: %s from %s", iface->name, msg, inet_ntoa(*from));
 	free(a);
 }
 
@@ -463,7 +463,7 @@ whitelisted_ip(const struct if_options *ifo, in_addr_t addr)
 }
 
 static void
-handle_dhcp(struct interface *iface, struct dhcp_message **dhcpp)
+handle_dhcp(struct interface *iface, struct dhcp_message **dhcpp, const struct in_addr *from)
 {
 	struct if_state *state = iface->state;
 	struct if_options *ifo = state->options;
@@ -485,11 +485,11 @@ handle_dhcp(struct interface *iface, struct dhcp_message **dhcpp)
 		if (has_option_mask(ifo->requiremask, DHO_SERVERID) &&
 		    get_option_addr(&addr, dhcp, DHO_SERVERID) == -1)
 		{
-			log_dhcp(LOG_WARNING, "reject NAK", iface, dhcp);
+			log_dhcp(LOG_WARNING, "reject NAK", iface, dhcp, from);
 			return;
 		}
 		/* We should restart on a NAK */
-		log_dhcp(LOG_WARNING, "NAK:", iface, dhcp);
+		log_dhcp(LOG_WARNING, "NAK:", iface, dhcp, from);
 		if (!(options & DHCPCD_TEST)) {
 			drop_config(iface, "NAK");
 			unlink(iface->leasefile);
@@ -512,7 +512,7 @@ handle_dhcp(struct interface *iface, struct dhcp_message **dhcpp)
 			 * To ignore bootp, require dhcp_message_type instead. */
 			if (type == 0 && i == DHO_SERVERID)
 				continue;
-			log_dhcp(LOG_WARNING, "reject DHCP", iface, dhcp);
+			log_dhcp(LOG_WARNING, "reject DHCP", iface, dhcp, from);
 			return;
 		}
 	}		
@@ -529,7 +529,7 @@ handle_dhcp(struct interface *iface, struct dhcp_message **dhcpp)
 		if (type == 0 ||
 		    get_option_addr(&lease->server, dhcp, DHO_SERVERID) != 0)
 			lease->server.s_addr = INADDR_ANY;
-		log_dhcp(LOG_INFO, "offered", iface, dhcp);
+		log_dhcp(LOG_INFO, "offered", iface, dhcp, from);
 		free(state->offer);
 		state->offer = dhcp;
 		*dhcpp = NULL;
@@ -558,18 +558,18 @@ handle_dhcp(struct interface *iface, struct dhcp_message **dhcpp)
 
 	if (type) {
 		if (type == DHCP_OFFER) {
-			log_dhcp(LOG_INFO, "ignoring offer of", iface, dhcp);
+			log_dhcp(LOG_INFO, "ignoring offer of", iface, dhcp, from);
 			return;
 		}
 
 		/* We should only be dealing with acks */
 		if (type != DHCP_ACK) {
-			log_dhcp(LOG_ERR, "not ACK or OFFER", iface, dhcp);
+			log_dhcp(LOG_ERR, "not ACK or OFFER", iface, dhcp, from);
 			return;
 		}
 
 		if (!(ifo->options & DHCPCD_INFORM))
-			log_dhcp(LOG_INFO, "acknowledged", iface, dhcp);
+			log_dhcp(LOG_INFO, "acknowledged", iface, dhcp, from);
 	}
 
 	/* BOOTP could have already assigned this above, so check we still
@@ -685,7 +685,7 @@ handle_dhcp_packet(void *arg)
 			    hwaddr_ntoa(dhcp->chaddr, sizeof(dhcp->chaddr)));
 			continue;
 		}
-		handle_dhcp(iface, &dhcp);
+		handle_dhcp(iface, &dhcp, &from);
 		if (iface->raw_fd == -1)
 			break;
 	}
-- 
1.6.6.2