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mDNS: probe rate limiting if more then 15 conflicts occur in 10s

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According to RFC6762 section 8.1:
If fifteen conflicts occur within any ten-second period, then the
host MUST wait at least five seconds before each successive
additional probe attempt.
If the host restarts mDNS, instead of a probe wait timeout randomly
chosen between 0 and 250ms, we wait 5s if more then 15 conflicts
occured in 10seconds. This flag is reset from the moment probing
succeeded.
This commit is contained in:
Jasper Verschueren 2018-11-19 10:59:16 +01:00 committed by Dirk Ziegelmeier
parent 593c02aed4
commit 19cbf2a652
2 changed files with 78 additions and 6 deletions
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68
src/apps/mdns/mdns.c
View File

@ -65,6 +65,7 @@
#include "lwip/prot/dns.h"
#include "lwip/prot/iana.h"
#include "lwip/timeouts.h"
#include "lwip/sys.h"
#include <string.h>
@ -1629,6 +1630,53 @@ mdns_handle_question(struct mdns_packet *pkt, struct netif *netif)
}
}
/**
* Handle a probe conflict:
* - Check if we exceeded the maximum of 15 conflicts in 10seconds.
* - Let the user know there is a conflict.
*
* @param netif network interface on which the conflict occured.
*/
static void
mdns_probe_conflict(struct netif *netif)
{
struct mdns_host* mdns = NETIF_TO_HOST(netif);
int i;
u32_t diff;
u8_t index2;
/* Disable currently running probe / announce timer */
sys_untimeout(mdns_probe_and_announce, netif);
/* Increase the number of conflicts occured */
mdns->num_conflicts++;
mdns->conflict_time[mdns->index] = sys_now();
/* Print timestamp list */
LWIP_DEBUGF(MDNS_DEBUG, ("mDNS: conflict timestamp list, insert index = %d\n", mdns->index));
for(i = 0; i < MDNS_PROBE_MAX_CONFLICTS_BEFORE_RATE_LIMIT; i++) {
LWIP_DEBUGF(MDNS_DEBUG, ("mDNS: time no. %d = %d\n", i, mdns->conflict_time[i]));
}
/* Check if we had enough conflicts, minimum 15 */
if (mdns->num_conflicts >= MDNS_PROBE_MAX_CONFLICTS_BEFORE_RATE_LIMIT) {
/* Get the index to the oldest timestamp */
index2 = (mdns->index + 1) % MDNS_PROBE_MAX_CONFLICTS_BEFORE_RATE_LIMIT;
/* Compare the oldest vs newest time stamp */
diff = mdns->conflict_time[mdns->index] - mdns->conflict_time[index2];
/* If they are less then 10 seconds apart, initiate rate limit */
if (diff < MDNS_PROBE_MAX_CONFLICTS_TIME_WINDOW) {
LWIP_DEBUGF(MDNS_DEBUG, ("mDNS: probe rate limit enabled\n"));
mdns->rate_limit_activated = 1;
}
}
/* Increase index */
mdns->index = (mdns->index + 1) % MDNS_PROBE_MAX_CONFLICTS_BEFORE_RATE_LIMIT;
/* Inform the host on the conflict, if a callback is set */
if (mdns_name_result_cb != NULL) {
mdns_name_result_cb(netif, MDNS_PROBING_CONFLICT);
}
}
/**
* Handle response MDNS packet
* Only prints debug for now. Will need more code to do conflict resolution.
@ -1698,10 +1746,7 @@ mdns_handle_response(struct mdns_packet *pkt, struct netif *netif)
}
if (conflict != 0) {
sys_untimeout(mdns_probe_and_announce, netif);
if (mdns_name_result_cb != NULL) {
mdns_name_result_cb(netif, MDNS_PROBING_CONFLICT);
}
mdns_probe_conflict(netif);
}
}
}
@ -1921,6 +1966,8 @@ mdns_probe_and_announce(void* arg)
if (mdns->sent_num == 0) {
/* probing was succesful, announce all records */
mdns->state = MDNS_STATE_ANNOUNCING;
/* Reset rate limit max probe conflict timeout flag */
mdns->rate_limit_activated = 0;
/* Let the client know probing was successful */
if (mdns_name_result_cb != NULL) {
mdns_name_result_cb(netif, MDNS_PROBING_SUCCESSFUL);
@ -2279,10 +2326,19 @@ mdns_resp_restart(struct netif *netif)
/* Make sure timer is not running */
sys_untimeout(mdns_probe_and_announce, netif);
/* @todo if we've failed 15 times within a 10 second period we MUST wait 5 seconds (or wait 5 seconds every time except first)*/
mdns->sent_num = 0;
mdns->state = MDNS_STATE_PROBE_WAIT;
sys_timeout(MDNS_INITIAL_PROBE_DELAY_MS, mdns_probe_and_announce, netif);
/* RFC6762 section 8.1: If fifteen conflicts occur within any ten-second period,
* then the host MUST wait at least five seconds before each successive
* additional probe attempt.
*/
if (mdns->rate_limit_activated == 1) {
sys_timeout(MDNS_PROBE_MAX_CONFLICTS_TIMEOUT, mdns_probe_and_announce, netif);
}
else {
sys_timeout(MDNS_INITIAL_PROBE_DELAY_MS, mdns_probe_and_announce, netif);
}
}
/**

16
src/include/lwip/apps/mdns_priv.h
View File

@ -64,6 +64,14 @@ extern "C" {
#define MDNS_TTL_120 120
#define MDNS_TTL_4500 4500
/* RFC6762 section 8.1: If fifteen conflicts occur within any ten-second period,
* then the host MUST wait at least five seconds before each successive
* additional probe attempt.
*/
#define MDNS_PROBE_MAX_CONFLICTS_BEFORE_RATE_LIMIT 15
#define MDNS_PROBE_MAX_CONFLICTS_TIME_WINDOW 10000
#define MDNS_PROBE_MAX_CONFLICTS_TIMEOUT 5000
/* Domain structs - also visible for unit tests */
struct mdns_domain {
@ -196,6 +204,14 @@ struct mdns_host {
/** delayed msg struct for IPv6 */
struct mdns_delayed_msg ipv6;
#endif
/** Timestamp of probe conflict saved in list */
u32_t conflict_time[MDNS_PROBE_MAX_CONFLICTS_BEFORE_RATE_LIMIT];
/** Rate limit flag */
u8_t rate_limit_activated;
/** List index for timestamps */
u8_t index;
/** number of conflicts since startup */
u8_t num_conflicts;
};
struct mdns_host* netif_mdns_data(struct netif *netif);