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mass_dns: Be more aggressive with timeouts but slower to increase capacity.

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dmiller
2024-05-13 14:31:34 +00:00
parent 37e0f7f80b
commit a626407796
1 changed files with 64 additions and 34 deletions
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92
nmap_dns.cc
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@@ -168,17 +168,19 @@ extern NmapOps o;
// In milliseconds
// Each row MUST be terminated with -1
static int read_timeouts[][4] = {
{ 4000, 4000, 5000, -1 }, // 1 server
{ 2500, 4000, -1, -1 }, // 2 servers
{ 2500, 3000, -1, -1 }, // 3+ servers
#define MAX_DNS_TRIES 3
#define MIN_DNS_TIMEOUT (MIN_RTT_TIMEOUT * 3)
static int read_timeouts[][MAX_DNS_TRIES + 1] = {
{ 2 * MIN_DNS_TIMEOUT, 30 * MIN_DNS_TIMEOUT, 40 * MIN_DNS_TIMEOUT, -1 }, // 1 server
{ 2 * MIN_DNS_TIMEOUT, 20 * MIN_DNS_TIMEOUT, -1, -1 }, // 2 servers
{ MIN_DNS_TIMEOUT, 10 * MIN_DNS_TIMEOUT, -1, -1 }, // 3+ servers
};
#define CAPACITY_MIN 10
#define CAPACITY_MAX 200
#define CAPACITY_MAX 100
#define CAPACITY_UP_STEP 2
#define CAPACITY_MINOR_DOWN_SCALE 0.9
#define CAPACITY_MAJOR_DOWN_SCALE 0.7
#define CAPACITY_MINOR_DOWN_SCALE 0.5
#define CAPACITY_MAJOR_DOWN_SCALE 0.2
// Each request will try to resolve on at most this many servers:
#define SERVERS_TO_TRY 3
@@ -212,14 +214,22 @@ struct dns_server {
int connected;
int reqs_on_wire;
int capacity;
int max_capacity;
int write_busy;
std::list<request *> to_process;
std::list<request *> in_process;
struct timeval last_increase;
dns_server() : hostname(), addr_len(0), connected(0), reqs_on_wire(0),
capacity(CAPACITY_MIN), max_capacity(CAPACITY_MAX), write_busy(0), to_process(), in_process()
{
memset(&addr, 0, sizeof(addr));
memset(&last_increase, 0, sizeof(last_increase));
}
};
struct request {
DNS::Request *targ;
struct timeval timeout;
struct timeval sent;
int tries;
int servers_tried;
dns_server *first_server;
@@ -414,7 +424,8 @@ static void output_summary() {
static void check_capacities(dns_server *tpserv) {
if (tpserv->capacity < CAPACITY_MIN) tpserv->capacity = CAPACITY_MIN;
if (tpserv->capacity > CAPACITY_MAX) tpserv->capacity = CAPACITY_MAX;
if (tpserv->max_capacity > CAPACITY_MAX) tpserv->max_capacity = CAPACITY_MAX;
if (tpserv->capacity > tpserv->max_capacity) tpserv->capacity = tpserv->max_capacity;
if (o.debugging >= TRACE_DEBUG_LEVEL) log_write(LOG_STDOUT, "CAPACITY <%s> = %d\n", tpserv->hostname.c_str(), tpserv->capacity);
}
@@ -430,9 +441,9 @@ static void close_dns_servers() {
serverI->in_process.clear();
}
}
nsock_loop_quit(dnspool);
}
// Puts as many packets on the line as capacity will allow
static void do_possible_writes() {
std::list<dns_server>::iterator servI;
@@ -491,8 +502,6 @@ static void put_dns_packet_on_wire(request *req) {
u8 packet[maxlen];
size_t plen=0;
struct timeval now, timeout;
req->curr_server->write_busy = 1;
req->curr_server->reqs_on_wire++;
DNS::Request &reqt = *req->targ;
@@ -511,18 +520,14 @@ static void put_dns_packet_on_wire(request *req) {
break;
}
memcpy(&now, nsock_gettimeofday(), sizeof(struct timeval));
TIMEVAL_MSEC_ADD(timeout, now, read_timeouts[read_timeout_index][req->tries]);
memcpy(&req->timeout, &timeout, sizeof(struct timeval));
req->tries++;
memcpy(&req->sent, nsock_gettimeofday(), sizeof(struct timeval));
nsock_write(dnspool, req->curr_server->nsd, write_evt_handler, WRITE_TIMEOUT, req, reinterpret_cast<const char *>(packet), plen);
}
// Processes DNS packets that have timed out
// Returns time until next read timeout
static int deal_with_timedout_reads() {
static int deal_with_timedout_reads(bool adjust_timing) {
std::list<dns_server>::iterator servI;
std::list<dns_server>::iterator servItemp;
std::list<request *>::iterator reqI;
@@ -541,24 +546,39 @@ static int deal_with_timedout_reads() {
nextI = servI->in_process.begin();
if (nextI == servI->in_process.end()) continue;
struct timeval earliest_sent = now;
bool adjusted = false;
bool may_increase = adjust_timing;
do {
reqI = nextI++;
tpreq = *reqI;
tp = TIMEVAL_MSEC_SUBTRACT(tpreq->timeout, now);
if (tp > 0 && tp < min_timeout) min_timeout = tp;
int to = read_timeouts[read_timeout_index][tpreq->tries];
if (tp <= 0) {
servI->capacity = (int) (servI->capacity * CAPACITY_MINOR_DOWN_SCALE);
check_capacities(&*servI);
int elapsed = TIMEVAL_MSEC_SUBTRACT(now, tpreq->sent);
tp = to - elapsed;
if (tp > 0) {
// only bother checking this if we might increase the capacity
if (may_increase && TIMEVAL_BEFORE(tpreq->sent, earliest_sent)) {
earliest_sent = tpreq->sent;
}
if (tp < min_timeout) min_timeout = tp;
}
else {
may_increase = false;
tpreq->tries++;
servI->in_process.erase(reqI);
records.erase(tpreq->id);
servI->reqs_on_wire--;
// If we've tried this server enough times, move to the next one
if (read_timeouts[read_timeout_index][tpreq->tries] == -1) {
if (!adjusted) {
servI->max_capacity = servI->capacity * 1.5;
servI->capacity = (int) (servI->capacity * CAPACITY_MAJOR_DOWN_SCALE);
check_capacities(&*servI);
adjusted = true;
}
servItemp = servI;
servItemp++;
@@ -591,6 +611,12 @@ static int deal_with_timedout_reads() {
servItemp->to_process.push_back(tpreq);
}
} else {
if (!adjusted) {
servI->max_capacity = servI->capacity * 2;
servI->capacity = (int) (servI->capacity * CAPACITY_MINOR_DOWN_SCALE);
check_capacities(&*servI);
adjusted = true;
}
servI->to_process.push_back(tpreq);
}
@@ -598,6 +624,11 @@ static int deal_with_timedout_reads() {
} while (nextI != servI->in_process.end());
if (may_increase && TIMEVAL_MSEC_SUBTRACT(earliest_sent, servI->last_increase) > (2 * MIN_DNS_TIMEOUT) && servI->reqs_on_wire > servI->capacity - CAPACITY_UP_STEP) {
servI->capacity += CAPACITY_UP_STEP;
check_capacities(&*servI);
servI->last_increase = now;
}
}
if (min_timeout > 500) return 500;
@@ -612,8 +643,10 @@ static void process_request(int action, info &reqinfo) {
switch (action) {
case ACTION_SYSTEM_RESOLVE:
case ACTION_FINISHED:
server->capacity += CAPACITY_UP_STEP;
check_capacities(&*server);
if (server->reqs_on_wire == server->capacity && server->capacity * 2 < server->max_capacity) {
server->capacity++;
check_capacities(server);
}
records.erase(tpreq->id);
server->in_process.remove(tpreq);
server->reqs_on_wire--;
@@ -628,8 +661,8 @@ static void process_request(int action, info &reqinfo) {
break;
case ACTION_TIMEOUT:
memcpy(&tpreq->timeout, nsock_gettimeofday(), sizeof(struct timeval));
deal_with_timedout_reads();
tpreq->tries = MAX_DNS_TRIES;
deal_with_timedout_reads(false);
break;
default:
assert(false);
@@ -876,9 +909,6 @@ static void connect_dns_servers() {
}
if (o.ipoptionslen)
nsock_iod_set_ipoptions(serverI->nsd, o.ipoptions, o.ipoptionslen);
serverI->reqs_on_wire = 0;
serverI->capacity = CAPACITY_MIN;
serverI->write_busy = 0;
nsock_connect_udp(dnspool, serverI->nsd, connect_evt_handler, NULL, (struct sockaddr *) &serverI->addr, serverI->addr_len, 53);
nsock_read(dnspool, serverI->nsd, read_evt_handler, -1, NULL);
@@ -1232,7 +1262,7 @@ static void nmap_mass_dns_core(DNS::Request *requests, int num_requests) {
stat_actual = total_reqs;
while (total_reqs > 0) {
timeout = deal_with_timedout_reads();
timeout = deal_with_timedout_reads(true);
do_possible_writes();