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authorBeniamino Galvani <bgalvani@redhat.com>2016-01-27 11:21:23 +0100
committerBeniamino Galvani <bgalvani@redhat.com>2016-02-02 15:23:34 +0100
commit1d1a3e0afb85478cda43670b8ed92a6db6c83f3e (patch)
tree97b240693fba36064c44c19b458031a3089f7beb
parentcd72d2044ad28b475bf84a38ba6db45292467dd8 (diff)
dhcp: delay restarts after NAKs
The server might answer to a DHCPREQUEST with a NAK and currently the client restarts the configuration process immediately. It was observed that this can easily generate loops in which the network is flooded with DISCOVER,OFFER,REQUEST,NAK sequences. RFC 2131 only states that "if the client receives a DHCPNAK message, the client restarts the configuration process" without further details. Add a delay with exponential backoff between retries after NAKs to limit the number of requests and cap the delay to 30 minutes.
-rw-r--r--src/libsystemd-network/sd-dhcp-client.c29
1 files changed, 25 insertions, 4 deletions
diff --git a/src/libsystemd-network/sd-dhcp-client.c b/src/libsystemd-network/sd-dhcp-client.c
index d3ad6b7717..cad1a52c09 100644
--- a/src/libsystemd-network/sd-dhcp-client.c
+++ b/src/libsystemd-network/sd-dhcp-client.c
@@ -43,6 +43,9 @@
#define MAX_CLIENT_ID_LEN (sizeof(uint32_t) + MAX_DUID_LEN) /* Arbitrary limit */
#define MAX_MAC_ADDR_LEN CONST_MAX(INFINIBAND_ALEN, ETH_ALEN)
+#define RESTART_AFTER_NAK_MIN_USEC (1 * USEC_PER_SEC)
+#define RESTART_AFTER_NAK_MAX_USEC (30 * USEC_PER_MINUTE)
+
struct sd_dhcp_client {
unsigned n_ref;
@@ -101,6 +104,7 @@ struct sd_dhcp_client {
sd_dhcp_client_cb_t cb;
void *userdata;
sd_dhcp_lease *lease;
+ usec_t start_delay;
};
static const uint8_t default_req_opts[] = {
@@ -945,6 +949,7 @@ error:
}
static int client_initialize_time_events(sd_dhcp_client *client) {
+ uint64_t usec = 0;
int r;
assert(client);
@@ -952,10 +957,15 @@ static int client_initialize_time_events(sd_dhcp_client *client) {
client->timeout_resend = sd_event_source_unref(client->timeout_resend);
+ if (client->start_delay) {
+ sd_event_now(client->event, clock_boottime_or_monotonic(), &usec);
+ usec += client->start_delay;
+ }
+
r = sd_event_add_time(client->event,
&client->timeout_resend,
clock_boottime_or_monotonic(),
- 0, 0,
+ usec, 0,
client_timeout_resend, client);
if (r < 0)
goto error;
@@ -985,7 +995,7 @@ static int client_initialize_events(sd_dhcp_client *client,
return 0;
}
-static int client_start(sd_dhcp_client *client) {
+static int client_start_delayed(sd_dhcp_client *client) {
int r;
assert_return(client, -EINVAL);
@@ -1013,6 +1023,11 @@ static int client_start(sd_dhcp_client *client) {
return client_initialize_events(client, client_receive_message_raw);
}
+static int client_start(sd_dhcp_client *client) {
+ client->start_delay = 0;
+ return client_start_delayed(client);
+}
+
static int client_timeout_expire(sd_event_source *s, uint64_t usec,
void *userdata) {
sd_dhcp_client *client = userdata;
@@ -1362,6 +1377,7 @@ static int client_set_lease_timeouts(sd_dhcp_client *client) {
static int client_handle_message(sd_dhcp_client *client, DHCPMessage *message,
int len) {
DHCP_CLIENT_DONT_DESTROY(client);
+ char time_string[FORMAT_TIMESPAN_MAX];
int r = 0, notify_event = 0;
assert(client);
@@ -1409,6 +1425,7 @@ static int client_handle_message(sd_dhcp_client *client, DHCPMessage *message,
r = client_handle_ack(client, message, len);
if (r >= 0) {
+ client->start_delay = 0;
client->timeout_resend =
sd_event_source_unref(client->timeout_resend);
client->receive_message =
@@ -1458,11 +1475,15 @@ static int client_handle_message(sd_dhcp_client *client, DHCPMessage *message,
if (r < 0)
goto error;
- r = client_start(client);
+ r = client_start_delayed(client);
if (r < 0)
goto error;
- log_dhcp_client(client, "REBOOTED");
+ log_dhcp_client(client, "REBOOT in %s", format_timespan(time_string, FORMAT_TIMESPAN_MAX,
+ client->start_delay, USEC_PER_SEC));
+
+ client->start_delay = CLAMP(client->start_delay * 2,
+ RESTART_AFTER_NAK_MIN_USEC, RESTART_AFTER_NAK_MAX_USEC);
return 0;
} else if (r == -ENOMSG)