[systemd-devel] [PATCH] sd-dhcp-client: fix REBOOT state handling

[Dan Williams]

client->secs wasn't getting set in the REBOOT state, causing
an assertion.  REBOOT should work the same way as INIT, per
RFC 2131:

 secs   2  Filled in by client, seconds elapsed since client
           began address acquisition or renewal process.

REBOOT is necessary because some DHCP servers (eg on
home routers) do not hand back the same IP address unless the
'ciaddr' field is filled with that address, which DISCOVER
cannot do per the RFCs.  This leads to multiple leases
on machine reboot or DHCP client restart.
---
 src/libsystemd-network/sd-dhcp-client.c | 31 +++++++++++++------------------
 1 file changed, 13 insertions(+), 18 deletions(-)

diff --git a/src/libsystemd-network/sd-dhcp-client.c b/src/libsystemd-network/sd-dhcp-client.c
index a8ec654..300fc38 100644
--- a/src/libsystemd-network/sd-dhcp-client.c
+++ b/src/libsystemd-network/sd-dhcp-client.c
@@ -89,7 +89,6 @@ struct sd_dhcp_client {
         uint32_t mtu;
         uint32_t xid;
         usec_t start_time;
-        uint16_t secs;
         unsigned int attempt;
         usec_t request_sent;
         sd_event_source *timeout_t1;
@@ -399,10 +398,12 @@ static int client_message_init(sd_dhcp_client *client, DHCPPacket **ret,
         _cleanup_free_ DHCPPacket *packet;
         size_t optlen, optoffset, size;
         be16_t max_size;
+        usec_t time_now;
+        uint16_t secs;
         int r;
 
         assert(client);
-        assert(client->secs);
+        assert(client->start_time);
         assert(ret);
         assert(_optlen);
         assert(_optoffset);
@@ -422,7 +423,15 @@ static int client_message_init(sd_dhcp_client *client, DHCPPacket **ret,
 
         /* Although 'secs' field is a SHOULD in RFC 2131, certain DHCP servers
            refuse to issue an DHCP lease if 'secs' is set to zero */
-        packet->dhcp.secs = htobe16(client->secs);
+        r = sd_event_now(client->event, clock_boottime_or_monotonic(), &time_now);
+        if (r < 0)
+                return r;
+        assert(time_now >= client->start_time);
+
+        /* seconds between sending first and last DISCOVER
+         * must always be strictly positive to deal with broken servers */
+        secs = ((time_now - client->start_time) / USEC_PER_SEC) ? : 1;
+        packet->dhcp.secs = htobe16(secs);
 
         /* RFC2132 section 4.1
            A client that cannot receive unicast IP datagrams until its protocol
@@ -529,24 +538,12 @@ static int dhcp_client_send_raw(sd_dhcp_client *client, DHCPPacket *packet,
 static int client_send_discover(sd_dhcp_client *client) {
         _cleanup_free_ DHCPPacket *discover = NULL;
         size_t optoffset, optlen;
-        usec_t time_now;
         int r;
 
         assert(client);
         assert(client->state == DHCP_STATE_INIT ||
                client->state == DHCP_STATE_SELECTING);
 
-        /* See RFC2131 section 4.4.1 */
-
-        r = sd_event_now(client->event, clock_boottime_or_monotonic(), &time_now);
-        if (r < 0)
-                return r;
-        assert(time_now >= client->start_time);
-
-        /* seconds between sending first and last DISCOVER
-         * must always be strictly positive to deal with broken servers */
-        client->secs = ((time_now - client->start_time) / USEC_PER_SEC) ? : 1;
-
         r = client_message_init(client, &discover, DHCP_DISCOVER,
                                 &optlen, &optoffset);
         if (r < 0)
@@ -963,10 +960,8 @@ static int client_start(sd_dhcp_client *client) {
         }
         client->fd = r;
 
-        if (client->state == DHCP_STATE_INIT) {
+        if (client->state == DHCP_STATE_INIT || client->state == DHCP_STATE_INIT_REBOOT)
                 client->start_time = now(clock_boottime_or_monotonic());
-                client->secs = 0;
-        }
 
         return client_initialize_events(client, client_receive_message_raw);
 }
-- 
1.9.3