ntpd: let user know if spike was detected
[oweals/busybox.git] / networking / udhcp / dhcpc.c
index d0fe94a481e5a098a6e8da2da81adb1e94474317..8dee916d9892cdb6d2eb249916109a8ccff9478c 100644 (file)
@@ -26,8 +26,8 @@
 #include "dhcpc.h"
 
 #include <netinet/if_ether.h>
-#include <netpacket/packet.h>
 #include <linux/filter.h>
+#include <linux/if_packet.h>
 
 /* "struct client_config_t client_config" is in bb_common_bufsiz1 */
 
@@ -46,7 +46,6 @@ static const char udhcpc_longopts[] ALIGN1 =
        "request\0"        Required_argument "r"
        "script\0"         Required_argument "s"
        "timeout\0"        Required_argument "T"
-       "version\0"        No_argument       "v"
        "retries\0"        Required_argument "t"
        "tryagain\0"       Required_argument "A"
        "syslog\0"         No_argument       "S"
@@ -102,6 +101,7 @@ static const uint8_t len_of_option_as_string[] = {
        [OPTION_STATIC_ROUTES   ] = sizeof("255.255.255.255/32 255.255.255.255 "),
        [OPTION_6RD             ] = sizeof("32 128 ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff 255.255.255.255 "),
        [OPTION_STRING          ] = 1,
+       [OPTION_STRING_HOST     ] = 1,
 #if ENABLE_FEATURE_UDHCP_RFC3397
        [OPTION_DNS_STRING      ] = 1, /* unused */
        /* Hmmm, this severely overestimates size if SIP_SERVERS option
@@ -124,24 +124,6 @@ static int sprint_nip(char *dest, const char *pre, const uint8_t *ip)
        return sprintf(dest, "%s%u.%u.%u.%u", pre, ip[0], ip[1], ip[2], ip[3]);
 }
 
-static int sprint_nip6(char *dest, /*const char *pre,*/ const uint8_t *ip)
-{
-       char hexstrbuf[16 * 2];
-       bin2hex(hexstrbuf, (void*)ip, 16);
-       return sprintf(dest, /* "%s" */
-               "%.4s:%.4s:%.4s:%.4s:%.4s:%.4s:%.4s:%.4s",
-               /* pre, */
-               hexstrbuf + 0 * 4,
-               hexstrbuf + 1 * 4,
-               hexstrbuf + 2 * 4,
-               hexstrbuf + 3 * 4,
-               hexstrbuf + 4 * 4,
-               hexstrbuf + 5 * 4,
-               hexstrbuf + 6 * 4,
-               hexstrbuf + 7 * 4
-       );
-}
-
 /* really simple implementation, just count the bits */
 static int mton(uint32_t mask)
 {
@@ -154,6 +136,63 @@ static int mton(uint32_t mask)
        return i;
 }
 
+/* Check if a given label represents a valid DNS label
+ * Return pointer to the first character after the label upon success,
+ * NULL otherwise.
+ * See RFC1035, 2.3.1
+ */
+/* We don't need to be particularly anal. For example, allowing _, hyphen
+ * at the end, or leading and trailing dots would be ok, since it
+ * can't be used for attacks. (Leading hyphen can be, if someone uses
+ * cmd "$hostname"
+ * in the script: then hostname may be treated as an option)
+ */
+static const char *valid_domain_label(const char *label)
+{
+       unsigned char ch;
+       unsigned pos = 0;
+
+       for (;;) {
+               ch = *label;
+               if ((ch|0x20) < 'a' || (ch|0x20) > 'z') {
+                       if (pos == 0) {
+                               /* label must begin with letter */
+                               return NULL;
+                       }
+                       if (ch < '0' || ch > '9') {
+                               if (ch == '\0' || ch == '.')
+                                       return label;
+                               /* DNS allows only '-', but we are more permissive */
+                               if (ch != '-' && ch != '_')
+                                       return NULL;
+                       }
+               }
+               label++;
+               pos++;
+               //Do we want this?
+               //if (pos > 63) /* NS_MAXLABEL; labels must be 63 chars or less */
+               //      return NULL;
+       }
+}
+
+/* Check if a given name represents a valid DNS name */
+/* See RFC1035, 2.3.1 */
+static int good_hostname(const char *name)
+{
+       //const char *start = name;
+
+       for (;;) {
+               name = valid_domain_label(name);
+               if (!name)
+                       return 0;
+               if (!name[0])
+                       return 1;
+                       //Do we want this?
+                       //return ((name - start) < 1025); /* NS_MAXDNAME */
+               name++;
+       }
+}
+
 /* Create "opt_name=opt_value" string */
 static NOINLINE char *xmalloc_optname_optval(uint8_t *option, const struct dhcp_optflag *optflag, const char *opt_name)
 {
@@ -206,8 +245,11 @@ static NOINLINE char *xmalloc_optname_optval(uint8_t *option, const struct dhcp_
                 * the case of list of options.
                 */
                case OPTION_STRING:
+               case OPTION_STRING_HOST:
                        memcpy(dest, option, len);
                        dest[len] = '\0';
+                       if (type == OPTION_STRING_HOST && !good_hostname(dest))
+                               safe_strncpy(dest, "bad", len);
                        return ret;
                case OPTION_STATIC_ROUTES: {
                        /* Option binary format:
@@ -387,6 +429,7 @@ static char **fill_envp(struct dhcp_packet *packet)
        /* +1 element for each option, +2 for subnet option: */
        if (packet) {
                /* note: do not search for "pad" (0) and "end" (255) options */
+//TODO: change logic to scan packet _once_
                for (i = 1; i < 255; i++) {
                        temp = udhcp_get_option(packet, i);
                        if (temp) {
@@ -499,9 +542,6 @@ static void udhcp_run_script(struct dhcp_packet *packet, const char *name)
        char **envp, **curr;
        char *argv[3];
 
-       if (client_config.script == NULL)
-               return;
-
        envp = fill_envp(packet);
 
        /* call script */
@@ -549,7 +589,6 @@ static void init_packet(struct dhcp_packet *packet, char type)
 
 static void add_client_options(struct dhcp_packet *packet)
 {
-       uint8_t c;
        int i, end, len;
 
        udhcp_add_simple_option(packet, DHCP_MAX_SIZE, htons(IP_UDP_DHCP_SIZE));
@@ -559,13 +598,9 @@ static void add_client_options(struct dhcp_packet *packet)
         * No bounds checking because it goes towards the head of the packet. */
        end = udhcp_end_option(packet->options);
        len = 0;
-       for (i = 0; (c = dhcp_optflags[i].code) != 0; i++) {
-               if ((   (dhcp_optflags[i].flags & OPTION_REQ)
-                    && !client_config.no_default_options
-                   )
-                || (client_config.opt_mask[c >> 3] & (1 << (c & 7)))
-               ) {
-                       packet->options[end + OPT_DATA + len] = c;
+       for (i = 1; i < DHCP_END; i++) {
+               if (client_config.opt_mask[i >> 3] & (1 << (i & 7))) {
+                       packet->options[end + OPT_DATA + len] = i;
                        len++;
                }
        }
@@ -632,6 +667,15 @@ static int raw_bcast_from_client_config_ifindex(struct dhcp_packet *packet)
                client_config.ifindex);
 }
 
+static int bcast_or_ucast(struct dhcp_packet *packet, uint32_t ciaddr, uint32_t server)
+{
+       if (server)
+               return udhcp_send_kernel_packet(packet,
+                       ciaddr, CLIENT_PORT,
+                       server, SERVER_PORT);
+       return raw_bcast_from_client_config_ifindex(packet);
+}
+
 /* Broadcast a DHCP discover packet to the network, with an optionally requested IP */
 /* NOINLINE: limit stack usage in caller */
 static NOINLINE int send_discover(uint32_t xid, uint32_t requested)
@@ -738,17 +782,13 @@ static NOINLINE int send_renew(uint32_t xid, uint32_t server, uint32_t ciaddr)
        add_client_options(&packet);
 
        bb_info_msg("Sending renew...");
-       if (server)
-               return udhcp_send_kernel_packet(&packet,
-                       ciaddr, CLIENT_PORT,
-                       server, SERVER_PORT);
-       return raw_bcast_from_client_config_ifindex(&packet);
+       return bcast_or_ucast(&packet, ciaddr, server);
 }
 
 #if ENABLE_FEATURE_UDHCPC_ARPING
 /* Broadcast a DHCP decline message */
 /* NOINLINE: limit stack usage in caller */
-static NOINLINE int send_decline(uint32_t xid, uint32_t server, uint32_t requested)
+static NOINLINE int send_decline(/*uint32_t xid,*/ uint32_t server, uint32_t requested)
 {
        struct dhcp_packet packet;
 
@@ -757,12 +797,14 @@ static NOINLINE int send_decline(uint32_t xid, uint32_t server, uint32_t request
         */
        init_packet(&packet, DHCPDECLINE);
 
+#if 0
        /* RFC 2131 says DHCPDECLINE's xid is randomly selected by client,
         * but in case the server is buggy and wants DHCPDECLINE's xid
         * to match the xid which started entire handshake,
         * we use the same xid we used in initial DHCPDISCOVER:
         */
        packet.xid = xid;
+#endif
        /* DHCPDECLINE uses "requested ip", not ciaddr, to store offered IP */
        udhcp_add_simple_option(&packet, DHCP_REQUESTED_IP, requested);
 
@@ -789,7 +831,11 @@ static int send_release(uint32_t server, uint32_t ciaddr)
        udhcp_add_simple_option(&packet, DHCP_SERVER_ID, server);
 
        bb_info_msg("Sending release...");
-       return udhcp_send_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
+       /* Note: normally we unicast here since "server" is not zero.
+        * However, there _are_ people who run "address-less" DHCP servers,
+        * and reportedly ISC dhcp client and Windows allow that.
+        */
+       return bcast_or_ucast(&packet, ciaddr, server);
 }
 
 /* Returns -1 on errors that are fatal for the socket, -2 for those that aren't */
@@ -799,13 +845,31 @@ static NOINLINE int udhcp_recv_raw_packet(struct dhcp_packet *dhcp_pkt, int fd)
        int bytes;
        struct ip_udp_dhcp_packet packet;
        uint16_t check;
+       unsigned char cmsgbuf[CMSG_LEN(sizeof(struct tpacket_auxdata))];
+       struct iovec iov;
+       struct msghdr msg;
+       struct cmsghdr *cmsg;
 
-       memset(&packet, 0, sizeof(packet));
-       bytes = safe_read(fd, &packet, sizeof(packet));
-       if (bytes < 0) {
-               log1("Packet read error, ignoring");
-               /* NB: possible down interface, etc. Caller should pause. */
-               return bytes; /* returns -1 */
+       /* used to use just safe_read(fd, &packet, sizeof(packet))
+        * but we need to check for TP_STATUS_CSUMNOTREADY :(
+        */
+       iov.iov_base = &packet;
+       iov.iov_len = sizeof(packet);
+       memset(&msg, 0, sizeof(msg));
+       msg.msg_iov = &iov;
+       msg.msg_iovlen = 1;
+       msg.msg_control = cmsgbuf;
+       msg.msg_controllen = sizeof(cmsgbuf);
+       for (;;) {
+               bytes = recvmsg(fd, &msg, 0);
+               if (bytes < 0) {
+                       if (errno == EINTR)
+                               continue;
+                       log1("Packet read error, ignoring");
+                       /* NB: possible down interface, etc. Caller should pause. */
+                       return bytes; /* returns -1 */
+               }
+               break;
        }
 
        if (bytes < (int) (sizeof(packet.ip) + sizeof(packet.udp))) {
@@ -842,6 +906,20 @@ static NOINLINE int udhcp_recv_raw_packet(struct dhcp_packet *dhcp_pkt, int fd)
                return -2;
        }
 
+       for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
+               if (cmsg->cmsg_level == SOL_PACKET
+                && cmsg->cmsg_type == PACKET_AUXDATA
+               ) {
+                       /* some VMs don't checksum UDP and TCP data
+                        * they send to the same physical machine,
+                        * here we detect this case:
+                        */
+                       struct tpacket_auxdata *aux = (void *)CMSG_DATA(cmsg);
+                       if (aux->tp_status & TP_STATUS_CSUMNOTREADY)
+                               goto skip_udp_sum_check;
+               }
+       }
+
        /* verify UDP checksum. IP header has to be modified for this */
        memset(&packet.ip, 0, offsetof(struct iphdr, protocol));
        /* ip.xx fields which are not memset: protocol, check, saddr, daddr */
@@ -852,13 +930,14 @@ static NOINLINE int udhcp_recv_raw_packet(struct dhcp_packet *dhcp_pkt, int fd)
                log1("Packet with bad UDP checksum received, ignoring");
                return -2;
        }
+ skip_udp_sum_check:
 
        if (packet.data.cookie != htonl(DHCP_MAGIC)) {
                bb_info_msg("Packet with bad magic, ignoring");
                return -2;
        }
 
-       log1("Got valid DHCP packet");
+       log1("Received a packet");
        udhcp_dump_packet(&packet.data);
 
        bytes -= sizeof(packet.ip) + sizeof(packet.udp);
@@ -947,7 +1026,7 @@ static int udhcp_raw_socket(int ifindex)
        log1("Opening raw socket on ifindex %d", ifindex); //log2?
 
        fd = xsocket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP));
-       log1("Got raw socket fd %d", fd); //log2?
+       log1("Got raw socket fd"); //log2?
 
        sock.sll_family = AF_PACKET;
        sock.sll_protocol = htons(ETH_P_IP);
@@ -959,7 +1038,14 @@ static int udhcp_raw_socket(int ifindex)
                /* Ignoring error (kernel may lack support for this) */
                if (setsockopt(fd, SOL_SOCKET, SO_ATTACH_FILTER, &filter_prog,
                                sizeof(filter_prog)) >= 0)
-                       log1("Attached filter to raw socket fd %d", fd); // log?
+                       log1("Attached filter to raw socket fd"); // log?
+       }
+
+       if (setsockopt(fd, SOL_PACKET, PACKET_AUXDATA,
+                       &const_int_1, sizeof(int)) < 0
+       ) {
+               if (errno != ENOPROTOOPT)
+                       log1("Can't set PACKET_AUXDATA on raw socket");
        }
 
        log1("Created raw socket");
@@ -1010,7 +1096,7 @@ static void perform_renew(void)
        }
 }
 
-static void perform_release(uint32_t requested_ip, uint32_t server_addr)
+static void perform_release(uint32_t server_addr, uint32_t requested_ip)
 {
        char buffer[sizeof("255.255.255.255")];
        struct in_addr temp_addr;
@@ -1058,34 +1144,35 @@ static void client_background(void)
 //usage:# define IF_UDHCP_VERBOSE(...)
 //usage:#endif
 //usage:#define udhcpc_trivial_usage
-//usage:       "[-fbnq"IF_UDHCP_VERBOSE("v")"oCRB] [-i IFACE] [-r IP] [-s PROG] [-p PIDFILE]\n"
-//usage:       "       [-H HOSTNAME] [-V VENDOR] [-x OPT:VAL]... [-O OPT]..." IF_FEATURE_UDHCP_PORT(" [-P N]")
+//usage:       "[-fbq"IF_UDHCP_VERBOSE("v")IF_FEATURE_UDHCPC_ARPING("a")"RB] [-t N] [-T SEC] [-A SEC/-n]\n"
+//usage:       "       [-i IFACE]"IF_FEATURE_UDHCP_PORT(" [-P PORT]")" [-s PROG] [-p PIDFILE]\n"
+//usage:       "       [-oC] [-r IP] [-V VENDOR] [-F NAME] [-x OPT:VAL]... [-O OPT]..."
 //usage:#define udhcpc_full_usage "\n"
 //usage:       IF_LONG_OPTS(
 //usage:     "\n       -i,--interface IFACE    Interface to use (default eth0)"
-//usage:     "\n       -p,--pidfile FILE       Create pidfile"
+//usage:       IF_FEATURE_UDHCP_PORT(
+//usage:     "\n       -P,--client-port PORT   Use PORT (default 68)"
+//usage:       )
 //usage:     "\n       -s,--script PROG        Run PROG at DHCP events (default "CONFIG_UDHCPC_DEFAULT_SCRIPT")"
+//usage:     "\n       -p,--pidfile FILE       Create pidfile"
 //usage:     "\n       -B,--broadcast          Request broadcast replies"
-//usage:     "\n       -t,--retries N          Send up to N discover packets"
-//usage:     "\n       -T,--timeout N          Pause between packets (default 3 seconds)"
-//usage:     "\n       -A,--tryagain N         Wait N seconds after failure (default 20)"
+//usage:     "\n       -t,--retries N          Send up to N discover packets (default 3)"
+//usage:     "\n       -T,--timeout SEC        Pause between packets (default 3)"
+//usage:     "\n       -A,--tryagain SEC       Wait if lease is not obtained (default 20)"
+//usage:     "\n       -n,--now                Exit if lease is not obtained"
+//usage:     "\n       -q,--quit               Exit after obtaining lease"
+//usage:     "\n       -R,--release            Release IP on exit"
 //usage:     "\n       -f,--foreground         Run in foreground"
 //usage:       USE_FOR_MMU(
 //usage:     "\n       -b,--background         Background if lease is not obtained"
 //usage:       )
-//usage:     "\n       -n,--now                Exit if lease is not obtained"
-//usage:     "\n       -q,--quit               Exit after obtaining lease"
-//usage:     "\n       -R,--release            Release IP on exit"
 //usage:     "\n       -S,--syslog             Log to syslog too"
-//usage:       IF_FEATURE_UDHCP_PORT(
-//usage:     "\n       -P,--client-port N      Use port N (default 68)"
-//usage:       )
 //usage:       IF_FEATURE_UDHCPC_ARPING(
 //usage:     "\n       -a,--arping             Use arping to validate offered address"
 //usage:       )
-//usage:     "\n       -O,--request-option OPT Request option OPT from server (cumulative)"
-//usage:     "\n       -o,--no-default-options Don't request any options (unless -O is given)"
 //usage:     "\n       -r,--request IP         Request this IP address"
+//usage:     "\n       -o,--no-default-options Don't request any options (unless -O is given)"
+//usage:     "\n       -O,--request-option OPT Request option OPT from server (cumulative)"
 //usage:     "\n       -x OPT:VAL              Include option OPT in sent packets (cumulative)"
 //usage:     "\n                               Examples of string, numeric, and hex byte opts:"
 //usage:     "\n                               -x hostname:bbox - option 12"
@@ -1100,29 +1187,29 @@ static void client_background(void)
 //usage:       )
 //usage:       IF_NOT_LONG_OPTS(
 //usage:     "\n       -i IFACE        Interface to use (default eth0)"
-//usage:     "\n       -p FILE         Create pidfile"
+//usage:       IF_FEATURE_UDHCP_PORT(
+//usage:     "\n       -P PORT         Use PORT (default 68)"
+//usage:       )
 //usage:     "\n       -s PROG         Run PROG at DHCP events (default "CONFIG_UDHCPC_DEFAULT_SCRIPT")"
+//usage:     "\n       -p FILE         Create pidfile"
 //usage:     "\n       -B              Request broadcast replies"
-//usage:     "\n       -t N            Send up to N discover packets"
-//usage:     "\n       -T N            Pause between packets (default 3 seconds)"
-//usage:     "\n       -A N            Wait N seconds (default 20) after failure"
+//usage:     "\n       -t N            Send up to N discover packets (default 3)"
+//usage:     "\n       -T SEC          Pause between packets (default 3)"
+//usage:     "\n       -A SEC          Wait if lease is not obtained (default 20)"
+//usage:     "\n       -n              Exit if lease is not obtained"
+//usage:     "\n       -q              Exit after obtaining lease"
+//usage:     "\n       -R              Release IP on exit"
 //usage:     "\n       -f              Run in foreground"
 //usage:       USE_FOR_MMU(
 //usage:     "\n       -b              Background if lease is not obtained"
 //usage:       )
-//usage:     "\n       -n              Exit if lease is not obtained"
-//usage:     "\n       -q              Exit after obtaining lease"
-//usage:     "\n       -R              Release IP on exit"
 //usage:     "\n       -S              Log to syslog too"
-//usage:       IF_FEATURE_UDHCP_PORT(
-//usage:     "\n       -P N            Use port N (default 68)"
-//usage:       )
 //usage:       IF_FEATURE_UDHCPC_ARPING(
 //usage:     "\n       -a              Use arping to validate offered address"
 //usage:       )
-//usage:     "\n       -O OPT          Request option OPT from server (cumulative)"
-//usage:     "\n       -o              Don't request any options (unless -O is given)"
 //usage:     "\n       -r IP           Request this IP address"
+//usage:     "\n       -o              Don't request any options (unless -O is given)"
+//usage:     "\n       -O OPT          Request option OPT from server (cumulative)"
 //usage:     "\n       -x OPT:VAL      Include option OPT in sent packets (cumulative)"
 //usage:     "\n                       Examples of string, numeric, and hex byte opts:"
 //usage:     "\n                       -x hostname:bbox - option 12"
@@ -1136,8 +1223,8 @@ static void client_background(void)
 //usage:       )
 //usage:       )
 //usage:     "\nSignals:"
-//usage:     "\n       USR1    Renew current lease"
-//usage:     "\n       USR2    Release current lease"
+//usage:     "\n       USR1    Renew lease"
+//usage:     "\n       USR2    Release lease"
 
 
 int udhcpc_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
@@ -1154,16 +1241,13 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
        int discover_retries = 3;
        uint32_t server_addr = server_addr; /* for compiler */
        uint32_t requested_ip = 0;
-       uint32_t xid = 0;
-       uint32_t lease_seconds = 0; /* can be given as 32-bit quantity */
+       uint32_t xid = xid; /* for compiler */
        int packet_num;
        int timeout; /* must be signed */
        unsigned already_waited_sec;
        unsigned opt;
        int max_fd;
        int retval;
-       struct timeval tv;
-       struct dhcp_packet packet;
        fd_set rfds;
 
        /* Default options */
@@ -1190,7 +1274,7 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
                , &list_x
                IF_FEATURE_UDHCP_PORT(, &str_P)
                IF_UDHCP_VERBOSE(, &dhcp_verbose)
-               );
+       );
        if (opt & (OPT_h|OPT_H)) {
                //msg added 2011-11
                bb_error_msg("option -h NAME is deprecated, use -x hostname:NAME");
@@ -1219,8 +1303,6 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
                SERVER_PORT = CLIENT_PORT - 1;
        }
 #endif
-       if (opt & OPT_o)
-               client_config.no_default_options = 1;
        while (list_O) {
                char *optstr = llist_pop(&list_O);
                unsigned n = bb_strtou(optstr, NULL, 0);
@@ -1230,6 +1312,14 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
                }
                client_config.opt_mask[n >> 3] |= 1 << (n & 7);
        }
+       if (!(opt & OPT_o)) {
+               unsigned i, n;
+               for (i = 0; (n = dhcp_optflags[i].code) != 0; i++) {
+                       if (dhcp_optflags[i].flags & OPTION_REQ) {
+                               client_config.opt_mask[n >> 3] |= 1 << (n & 7);
+                       }
+               }
+       }
        while (list_x) {
                char *optstr = llist_pop(&list_x);
                char *colon = strchr(optstr, ':');
@@ -1303,6 +1393,8 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
         * "continue" statements in code below jump to the top of the loop.
         */
        for (;;) {
+               struct timeval tv;
+               struct dhcp_packet packet;
                /* silence "uninitialized!" warning */
                unsigned timestamp_before_wait = timestamp_before_wait;
 
@@ -1322,8 +1414,8 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
                retval = 0;
                /* If we already timed out, fall through with retval = 0, else... */
                if ((int)tv.tv_sec > 0) {
+                       log1("Waiting on select %u seconds", (int)tv.tv_sec);
                        timestamp_before_wait = (unsigned)monotonic_sec();
-                       log1("Waiting on select...");
                        retval = select(max_fd + 1, &rfds, NULL, NULL, &tv);
                        if (retval < 0) {
                                /* EINTR? A signal was caught, don't panic */
@@ -1350,7 +1442,7 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
                                        NULL,
                                        client_config.client_mac)
                        ) {
-                               return 1; /* iface is gone? */
+                               goto ret0; /* iface is gone? */
                        }
                        if (clientid_mac_ptr)
                                memcpy(clientid_mac_ptr, client_config.client_mac, 6);
@@ -1360,7 +1452,7 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
 
                        switch (state) {
                        case INIT_SELECTING:
-                               if (packet_num < discover_retries) {
+                               if (!discover_retries || packet_num < discover_retries) {
                                        if (packet_num == 0)
                                                xid = random_xid();
                                        /* broadcast */
@@ -1389,7 +1481,7 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
                                packet_num = 0;
                                continue;
                        case REQUESTING:
-                               if (packet_num < discover_retries) {
+                               if (!discover_retries || packet_num < discover_retries) {
                                        /* send broadcast select packet */
                                        send_select(xid, server_addr, requested_ip);
                                        timeout = discover_timeout;
@@ -1487,13 +1579,11 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
                        timeout = 0;
                        continue;
                case SIGUSR2:
-                       perform_release(requested_ip, server_addr);
+                       perform_release(server_addr, requested_ip);
                        timeout = INT_MAX;
                        continue;
                case SIGTERM:
                        bb_info_msg("Received SIGTERM");
-                       if (opt & OPT_R) /* release on quit */
-                               perform_release(requested_ip, server_addr);
                        goto ret0;
                }
 
@@ -1546,7 +1636,7 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
 
                switch (state) {
                case INIT_SELECTING:
-                       /* Must be a DHCPOFFER to one of our xid's */
+                       /* Must be a DHCPOFFER */
                        if (*message == DHCPOFFER) {
 /* What exactly is server's IP? There are several values.
  * Example DHCP offer captured with tchdump:
@@ -1567,14 +1657,19 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
  * might work too.
  * "Next server" and router are definitely wrong ones to use, though...
  */
+/* We used to ignore pcakets without DHCP_SERVER_ID.
+ * I've got user reports from people who run "address-less" servers.
+ * They either supply DHCP_SERVER_ID of 0.0.0.0 or don't supply it at all.
+ * They say ISC DHCP client supports this case.
+ */
+                               server_addr = 0;
                                temp = udhcp_get_option(&packet, DHCP_SERVER_ID);
                                if (!temp) {
-                                       bb_error_msg("no server ID, ignoring packet");
-                                       continue;
-                                       /* still selecting - this server looks bad */
+                                       bb_error_msg("no server ID, using 0.0.0.0");
+                               } else {
+                                       /* it IS unaligned sometimes, don't "optimize" */
+                                       move_from_unaligned32(server_addr, temp);
                                }
-                               /* it IS unaligned sometimes, don't "optimize" */
-                               move_from_unaligned32(server_addr, temp);
                                /*xid = packet.xid; - already is */
                                requested_ip = packet.yiaddr;
 
@@ -1590,6 +1685,9 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
                case RENEW_REQUESTED:
                case REBINDING:
                        if (*message == DHCPACK) {
+                               uint32_t lease_seconds;
+                               struct in_addr temp_addr;
+
                                temp = udhcp_get_option(&packet, DHCP_LEASE_TIME);
                                if (!temp) {
                                        bb_error_msg("no lease time with ACK, using 1 hour lease");
@@ -1598,9 +1696,11 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
                                        /* it IS unaligned sometimes, don't "optimize" */
                                        move_from_unaligned32(lease_seconds, temp);
                                        lease_seconds = ntohl(lease_seconds);
-                                       lease_seconds &= 0x0fffffff; /* paranoia: must not be prone to overflows */
-                                       if (lease_seconds < 10) /* and not too small */
-                                               lease_seconds = 10;
+                                       /* paranoia: must not be too small and not prone to overflows */
+                                       if (lease_seconds < 0x10)
+                                               lease_seconds = 0x10;
+                                       if (lease_seconds >= 0x10000000)
+                                               lease_seconds = 0x0fffffff;
                                }
 #if ENABLE_FEATURE_UDHCPC_ARPING
                                if (opt & OPT_a) {
@@ -1621,7 +1721,7 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
                                        ) {
                                                bb_info_msg("Offered address is in use "
                                                        "(got ARP reply), declining");
-                                               send_decline(xid, server_addr, packet.yiaddr);
+                                               send_decline(/*xid,*/ server_addr, packet.yiaddr);
 
                                                if (state != REQUESTING)
                                                        udhcp_run_script(NULL, "deconfig");
@@ -1638,20 +1738,15 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
 #endif
                                /* enter bound state */
                                timeout = lease_seconds / 2;
-                               {
-                                       struct in_addr temp_addr;
-                                       temp_addr.s_addr = packet.yiaddr;
-                                       bb_info_msg("Lease of %s obtained, lease time %u",
-                                               inet_ntoa(temp_addr), (unsigned)lease_seconds);
-                               }
+                               temp_addr.s_addr = packet.yiaddr;
+                               bb_info_msg("Lease of %s obtained, lease time %u",
+                                       inet_ntoa(temp_addr), (unsigned)lease_seconds);
                                requested_ip = packet.yiaddr;
                                udhcp_run_script(&packet, state == REQUESTING ? "bound" : "renew");
 
                                state = BOUND;
                                change_listen_mode(LISTEN_NONE);
                                if (opt & OPT_q) { /* quit after lease */
-                                       if (opt & OPT_R) /* release on quit */
-                                               perform_release(requested_ip, server_addr);
                                        goto ret0;
                                }
                                /* future renew failures should not exit (JM) */
@@ -1663,6 +1758,8 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
                                        opt = ((opt & ~OPT_b) | OPT_f);
                                }
 #endif
+                               /* make future renew packets use different xid */
+                               /* xid = random_xid(); ...but why bother? */
                                already_waited_sec = 0;
                                continue; /* back to main loop */
                        }
@@ -1689,6 +1786,8 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
        } /* for (;;) - main loop ends */
 
  ret0:
+       if (opt & OPT_R) /* release on quit */
+               perform_release(server_addr, requested_ip);
        retval = 0;
  ret:
        /*if (client_config.pidfile) - remove_pidfile has its own check */