udhcpc: an option to perform ARP check (Jonas Danielsson <jonas.danielsson@axis.com>)

configurable, ~+300 bytes when on.

include/usage.h

@@ -2183,8 +2183,8 @@
        "and * (run both after creating and before deleting). The commands run in\n" \
        "the /dev directory, and use system() which calls /bin/sh.\n\n" \
 	) \
-       "Config file parsing stops on the first matching line. If no config\n"\
+       "Config file parsing stops on the first matching line. If no config\n" \
-       "entry is matched, devices are created with default 0:0 660. (Make\n"\
+       "entry is matched, devices are created with default 0:0 660. (Make\n" \
        "the last line match .* to override this.)\n\n" \
 	)
 
@@ -3843,44 +3843,50 @@ USE_FEATURE_RUN_PARTS_FANCY("\n	-l	Prints names of all matching files even when
        "	[-p pidfile] [-r IP] [-s script]"
 #define udhcpc_full_usage \
 	USE_GETOPT_LONG( \
-       "	-V,--vendorclass=CLASSID	Set vendor class identifier" \
+       "	-V,--vendorclass=CLASSID	Vendor class identifier" \
-       "\n	-i,--interface=INTERFACE	Interface to use (default: eth0)" \
+       "\n	-i,--interface=INTERFACE	Interface to use (default eth0)" \
        "\n	-H,-h,--hostname=HOSTNAME	Client hostname" \
-       "\n	-c,--clientid=CLIENTID	Set client identifier" \
+       "\n	-c,--clientid=CLIENTID	Client identifier" \
        "\n	-C,--clientid-none	Suppress default client identifier" \
-       "\n	-p,--pidfile=file	Store process ID of daemon in file" \
+       "\n	-p,--pidfile=file	Create pidfile" \
        "\n	-r,--request=IP		IP address to request" \
        "\n	-s,--script=file	Run file at dhcp events (default: /usr/share/udhcpc/default.script)" \
-       "\n	-t,--retries=N		Send up to N request packets"\
+       "\n	-t,--retries=N		Send up to N request packets" \
-       "\n	-T,--timeout=N		Try to get a lease for N seconds (default: 3)"\
+       "\n	-T,--timeout=N		Try to get a lease for N seconds (default 3)" \
-       "\n	-A,--tryagain=N		Wait N seconds (default: 60) after failure"\
+       "\n	-A,--tryagain=N		Wait N seconds (default 60) after failure" \
        "\n	-f,--foreground	Run in foreground" \
-       "\n	-b,--background	Background if lease cannot be immediately negotiated" \
+       "\n	-b,--background	Background if lease is not immediately obtained" \
        "\n	-S,--syslog	Log to syslog too" \
-       "\n	-n,--now	Exit with failure if lease cannot be immediately negotiated" \
+       "\n	-n,--now	Exit with failure if lease is not immediately obtained" \
        "\n	-q,--quit	Quit after obtaining lease" \
        "\n	-R,--release	Release IP on quit" \
-       "\n	-v,--version	Display version" \
+	USE_FEATURE_UDHCPC_ARPING( \
+       "\n	-a,--arping	Use arping to validate offered address" \
+       "\n	-W,--wait=N	Wait N seconds after declining (default 10)" \
+	) \
 	) \
 	SKIP_GETOPT_LONG( \
-       "	-V CLASSID	Set vendor class identifier" \
+       "	-V CLASSID	Vendor class identifier" \
        "\n	-i INTERFACE	Interface to use (default: eth0)" \
        "\n	-H,-h HOSTNAME	Client hostname" \
-       "\n	-c CLIENTID	Set client identifier" \
+       "\n	-c CLIENTID	Client identifier" \
        "\n	-C		Suppress default client identifier" \
-       "\n	-p file		Store process ID of daemon in file" \
+       "\n	-p file		Create pidfile" \
        "\n	-r IP		IP address to request" \
        "\n	-s file		Run file at dhcp events (default: /usr/share/udhcpc/default.script)" \
-       "\n	-t N		Send up to N request packets"\
+       "\n	-t N		Send up to N request packets" \
-       "\n	-T N		Try to get a lease for N seconds (default: 3)"\
+       "\n	-T N		Try to get a lease for N seconds (default 3)" \
-       "\n	-A N		Wait N seconds (default: 60) after failure"\
+       "\n	-A N		Wait N seconds (default 60) after failure" \
        "\n	-f		Run in foreground" \
-       "\n	-b		Background if lease cannot be immediately negotiated" \
+       "\n	-b		Background if lease is not immediately obtained" \
        "\n	-S		Log to syslog too" \
-       "\n	-n		Exit with failure if lease cannot be immediately negotiated" \
+       "\n	-n		Exit with failure if lease is not immediately obtained" \
        "\n	-q		Quit after obtaining lease" \
        "\n	-R		Release IP on quit" \
-       "\n	-v		Display version" \
+	USE_FEATURE_UDHCPC_ARPING( \
+       "\n	-a		Use arping to validate offered address" \
+       "\n	-W N		Wait N seconds after declining (default 10)" \
+	) \
 	)
 
 #define udhcpd_trivial_usage \

networking/udhcp/Config.in

@@ -54,6 +54,16 @@ config APP_UDHCPC
 
 	  See http://udhcp.busybox.net for further details.
 
+config FEATURE_UDHCPC_ARPING
+	bool "Ask udhcpc to verify that the offered address is free, using arpping"
+	default y
+	depends on APP_UDHCPC
+	help
+	  If selected, udhcpc will use arpping to make sure the offered address
+	  is really available. The client will DHCPDECLINE the offer if the
+	  address is in use, and restart the discover process.
+
+
 config FEATURE_UDHCP_DEBUG
 	bool "Compile udhcp with noisy debugging messages"
 	default n

networking/udhcp/Kbuild

@@ -10,10 +10,16 @@ lib-$(CONFIG_APP_UDHCPC)        += common.o options.o packet.o \
                                    signalpipe.o socket.o
 lib-$(CONFIG_APP_UDHCPD)        += common.o options.o packet.o \
                                    signalpipe.o socket.o
+
 lib-$(CONFIG_APP_UDHCPC)        += dhcpc.o clientpacket.o clientsocket.o \
                                    script.o
+
+UDHCPC_NEEDS_ARPING-$(CONFIG_FEATURE_UDHCPC_ARPING) = y
+lib-$(UDHCPC_NEEDS_ARPING)      += arpping.o
+
 lib-$(CONFIG_APP_UDHCPD)        += dhcpd.o arpping.o files.o leases.o \
                                    serverpacket.o static_leases.o
+
 lib-$(CONFIG_APP_DUMPLEASES)    += dumpleases.o
 lib-$(CONFIG_APP_DHCPRELAY)     += dhcprelay.o
 lib-$(CONFIG_FEATURE_RFC3397)   += domain_codec.o

networking/udhcp/arpping.c

@@ -32,12 +32,16 @@ struct arpMsg {
 	uint8_t  pad[18];       /* 2a pad for min. ethernet payload (60 bytes) */
 } ATTRIBUTE_PACKED;
 
+enum {
+	ARP_MSG_SIZE = 0x2a
+};
+
 
 /* Returns 1 if no reply received */
 
 int arpping(uint32_t test_ip, uint32_t from_ip, uint8_t *from_mac, const char *interface)
 {
-	int timeout_ms = 2000;
+	int timeout_ms;
 	struct pollfd pfd[1];
 #define s (pfd[0].fd)           /* socket */
 	int rv = 1;             /* "no reply received" yet */
@@ -51,7 +55,7 @@ int arpping(uint32_t test_ip, uint32_t from_ip, uint8_t *from_mac, const char *i
 	}
 
 	if (setsockopt_broadcast(s) == -1) {
-		bb_perror_msg("cannot setsocketopt on raw socket");
+		bb_perror_msg("cannot enable bcast on raw socket");
 		goto ret;
 	}
 
@@ -67,28 +71,35 @@ int arpping(uint32_t test_ip, uint32_t from_ip, uint8_t *from_mac, const char *i
 	arp.operation = htons(ARPOP_REQUEST);           /* ARP op code */
 	memcpy(arp.sHaddr, from_mac, 6);                /* source hardware address */
 	memcpy(arp.sInaddr, &from_ip, sizeof(from_ip)); /* source IP address */
-	/* tHaddr */                                    /* target hardware address */
+	/* tHaddr is zero-fiiled */                     /* target hardware address */
 	memcpy(arp.tInaddr, &test_ip, sizeof(test_ip)); /* target IP address */
 
 	memset(&addr, 0, sizeof(addr));
 	safe_strncpy(addr.sa_data, interface, sizeof(addr.sa_data));
-	if (sendto(s, &arp, sizeof(arp), 0, &addr, sizeof(addr)) < 0)
+	if (sendto(s, &arp, sizeof(arp), 0, &addr, sizeof(addr)) < 0) {
+		// TODO: error message? caller didn't expect us to fail,
+		// just returning 1 "no reply received" misleads it.
 		goto ret;
+	}
 
 	/* wait for arp reply, and check it */
+	timeout_ms = 2000;
 	do {
 		int r;
 		unsigned prevTime = monotonic_us();
 
 		pfd[0].events = POLLIN;
 		r = safe_poll(pfd, 1, timeout_ms);
-		if (r < 0) {
+		if (r < 0)
 			break;
-		} else if (r) {
+		if (r) {
-			if (read(s, &arp, sizeof(arp)) < 0)
+			r = read(s, &arp, sizeof(arp));
+			if (r < 0)
 				break;
-			if (arp.operation == htons(ARPOP_REPLY)
+			if (r >= ARP_MSG_SIZE
-			 && memcmp(arp.tHaddr, from_mac, 6) == 0
+			 && arp.operation == htons(ARPOP_REPLY)
+			 /* don't check it: Linux doesn't return proper tHaddr (fixed in 2.6.24?) */
+			 /* && memcmp(arp.tHaddr, from_mac, 6) == 0 */
 			 && *((uint32_t *) arp.sInaddr) == test_ip
 			) {
 				rv = 0;

networking/udhcp/clientpacket.c

@@ -69,6 +69,22 @@ static void add_requests(struct dhcpMessage *packet)
 
 }
 
+#if ENABLE_FEATURE_UDHCPC_ARPING
+/* Unicast a DHCP decline message */
+int send_decline(uint32_t xid, uint32_t server)
+{
+	struct dhcpMessage packet;
+
+	init_packet(&packet, DHCPDECLINE);
+	packet.xid = xid;
+	add_requests(&packet);
+
+	bb_info_msg("Sending decline...");
+
+	return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
+		SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
+}
+#endif
 
 /* Broadcast a DHCP discover packet to the network, with an optionally requested IP */
 int send_discover(uint32_t xid, uint32_t requested)

networking/udhcp/common.h

@@ -76,7 +76,7 @@ void udhcp_run_script(struct dhcpMessage *packet, const char *name);
 
 void udhcp_sp_setup(void);
 int udhcp_sp_fd_set(fd_set *rfds, int extra_fd);
-int udhcp_sp_read(fd_set *rfds);
+int udhcp_sp_read(const fd_set *rfds);
 int raw_socket(int ifindex);
 int read_interface(const char *interface, int *ifindex, uint32_t *addr, uint8_t *arp);
 int listen_socket(/*uint32_t ip,*/ int port, const char *inf);

networking/udhcp/dhcpc.c

@@ -145,6 +145,13 @@ int udhcpc_main(int argc, char **argv)
 {
 	uint8_t *temp, *message;
 	char *str_c, *str_V, *str_h, *str_F, *str_r, *str_T, *str_A, *str_t;
+	int tryagain_timeout = 60;
+	int discover_timeout = 3;
+	int discover_retries = 3;
+#if ENABLE_FEATURE_UDHCPC_ARPING
+	int decline_wait = 10;
+	char *str_W;
+#endif
 	uint32_t xid = 0;
 	uint32_t lease = 0; /* can be given as 32-bit quantity */
 	unsigned t1 = 0, t2 = 0; /* what a wonderful names */
@@ -180,6 +187,10 @@ int udhcpc_main(int argc, char **argv)
 		OPT_v = 1 << 17,
 		OPT_S = 1 << 18,
 		OPT_A = 1 << 19,
+#if ENABLE_FEATURE_UDHCPC_ARPING
+		OPT_a = 1 << 20,
+		OPT_W = 1 << 21,
+#endif
 	};
 #if ENABLE_GETOPT_LONG
 	static const char udhcpc_longopts[] ALIGN1 =
@@ -203,14 +214,15 @@ int udhcpc_main(int argc, char **argv)
 		"retries\0"       Required_argument "t"
 		"tryagain\0"      Required_argument "A"
 		"syslog\0"        No_argument       "S"
+#if ENABLE_FEATURE_UDHCPC_ARPING
+		"arping\0"        No_argument       "a"
+		"wait\0"          Required_argument "W"
+#endif
 		;
 #endif
 	/* Default options. */
 	client_config.interface = "eth0";
 	client_config.script = DEFAULT_SCRIPT;
-	client_config.retries = 3;
-	client_config.timeout = 3;
-	client_config.tryagain = 60;
 
 	/* Parse command line */
 	opt_complementary = "c--C:C--c" // mutually exclusive
@@ -218,10 +230,12 @@ int udhcpc_main(int argc, char **argv)
 #if ENABLE_GETOPT_LONG
 	applet_long_options = udhcpc_longopts;
 #endif
-	opt = getopt32(argv, "c:CV:fbH:h:F:i:np:qRr:s:T:t:vSA:",
+	opt = getopt32(argv, "c:CV:fbH:h:F:i:np:qRr:s:T:t:vSA:"
-		&str_c, &str_V, &str_h, &str_h, &str_F,
+		USE_FEATURE_UDHCPC_ARPING("aW:")
+		, &str_c, &str_V, &str_h, &str_h, &str_F,
 		&client_config.interface, &client_config.pidfile, &str_r,
 		&client_config.script, &str_T, &str_t, &str_A
+		USE_FEATURE_UDHCPC_ARPING(, &str_W)
 		);
 
 	if (opt & OPT_c)
@@ -259,11 +273,11 @@ int udhcpc_main(int argc, char **argv)
 		requested_ip = inet_addr(str_r);
 	// if (opt & OPT_s) client_config.script = ...
 	if (opt & OPT_T)
-		client_config.timeout = xatoi_u(str_T);
+		discover_timeout = xatoi_u(str_T);
 	if (opt & OPT_t)
-		client_config.retries = xatoi_u(str_t);
+		discover_retries = xatoi_u(str_t);
 	if (opt & OPT_A)
-		client_config.tryagain = xatoi_u(str_A);
+		tryagain_timeout = xatoi_u(str_A);
 	if (opt & OPT_v) {
 		puts("version "BB_VER);
 		return 0;
@@ -274,6 +288,11 @@ int udhcpc_main(int argc, char **argv)
 		logmode |= LOGMODE_SYSLOG;
 	}
 
+#if ENABLE_FEATURE_UDHCPC_ARPING
+	if (opt & OPT_W)
+		decline_wait = xatou_range(str_W, 10, INT_MAX);
+#endif
+
 	if (read_interface(client_config.interface, &client_config.ifindex,
 			   NULL, client_config.arp))
 		return 1;
@@ -339,14 +358,14 @@ int udhcpc_main(int argc, char **argv)
 			/* timeout dropped to zero */
 			switch (state) {
 			case INIT_SELECTING:
-				if (packet_num < client_config.retries) {
+				if (packet_num < discover_retries) {
 					if (packet_num == 0)
 						xid = random_xid();
 
 					/* send discover packet */
 					send_discover(xid, requested_ip); /* broadcast */
 
-					timeout = now + client_config.timeout;
+					timeout = now + discover_timeout;
 					packet_num++;
 				} else {
 					udhcp_run_script(NULL, "leasefail");
@@ -360,12 +379,12 @@ int udhcpc_main(int argc, char **argv)
 					}
 					/* wait to try again */
 					packet_num = 0;
-					timeout = now + client_config.tryagain;
+					timeout = now + tryagain_timeout;
 				}
 				break;
 			case RENEW_REQUESTED:
 			case REQUESTING:
-				if (packet_num < client_config.retries) {
+				if (packet_num < discover_retries) {
 					/* send request packet */
 					if (state == RENEW_REQUESTED)
 						send_renew(xid, server_addr, requested_ip); /* unicast */
@@ -491,6 +510,28 @@ int udhcpc_main(int argc, char **argv)
 						lease = ntohl(lease);
 					}
 
+#if ENABLE_FEATURE_UDHCPC_ARPING
+					if (opt & OPT_a) {
+						if (!arpping(packet.yiaddr,
+							    (uint32_t) 0,
+							    client_config.arp,
+							    client_config.interface)
+						) {
+							bb_info_msg("offered address is in use,"
+								" declining");
+							send_decline(xid, server_addr);
+
+							if (state != REQUESTING)
+								udhcp_run_script(NULL, "deconfig");
+							state = INIT_SELECTING;
+							requested_ip = 0;
+							packet_num = 0;
+							change_mode(LISTEN_RAW);
+							timeout = now + decline_wait;
+							break;
+						}
+					}
+#endif
 					/* enter bound state */
 					t1 = lease / 2;
 

networking/udhcp/dhcpc.h

@@ -1,5 +1,6 @@
 /* vi: set sw=4 ts=4: */
 /* dhcpc.h */
+
 #ifndef _DHCPC_H
 #define _DHCPC_H
 
@@ -28,9 +29,6 @@ struct client_config_t {
 	uint8_t *hostname;              /* Optional hostname to use */
 	uint8_t *fqdn;                  /* Optional fully qualified domain name to use */
 	int ifindex;                    /* Index number of the interface to use */
-	int retries;                    /* Max number of request packets */
-	int timeout;                    /* Number of seconds to try to get a lease */
-	int tryagain;                   /* Number of seconds to try to get a lease */
 	uint8_t arp[6];                 /* Our arp address */
 };
 
@@ -42,6 +40,9 @@ struct client_config_t {
 uint32_t random_xid(void);
 int send_discover(uint32_t xid, uint32_t requested);
 int send_selecting(uint32_t xid, uint32_t server, uint32_t requested);
+#if ENABLE_FEATURE_UDHCPC_ARPING
+int send_decline(uint32_t xid, uint32_t server);
+#endif
 int send_renew(uint32_t xid, uint32_t server, uint32_t ciaddr);
 int send_renew(uint32_t xid, uint32_t server, uint32_t ciaddr);
 int send_release(uint32_t server, uint32_t ciaddr);

networking/udhcp/signalpipe.c

@@ -66,7 +66,7 @@ int udhcp_sp_fd_set(fd_set *rfds, int extra_fd)
 /* Read a signal from the signal pipe. Returns 0 if there is
  * no signal, -1 on error (and sets errno appropriately), and
  * your signal on success */
-int udhcp_sp_read(fd_set *rfds)
+int udhcp_sp_read(const fd_set *rfds)
 {
 	unsigned char sig;