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bug #50837: add zero-window probe timeout

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This commit adds a timeout to the zero-window probing (persist timer)
mechanism. LwIP has not historically had a timeout for the persist
timer, leading to unbounded blocking if connection drops during the
zero-window condition

This commit also adds two units test, one to check the RTO timeout
and a second to check the zero-window probe timeout
This commit is contained in:
Joel Cunningham 2017-05-03 23:43:49 -05:00
parent d87b11e8f9
commit c03fef9a3c
6 changed files with 214 additions and 13 deletions
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3
CHANGELOG
View File

@ -52,6 +52,9 @@ HISTORY
++ Bugfixes:
2017-05-09: Joel Cunningham
* tcp: add zero-window probe timeout (bug #50837)
2017-04-11: Simon Goldschmidt
* sockets.c: task #14420 (Remove sys_sem_signal from inside SYS_ARCH_PROTECT
crit section) done for LWIP_TCPIP_CORE_LOCKING==1

26
src/core/tcp.c
View File

@ -1072,17 +1072,21 @@ tcp_slowtmr_start:
LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: max DATA retries reached\n"));
} else {
if (pcb->persist_backoff > 0) {
/* If snd_wnd is zero, use persist timer to send 1 byte probes
* instead of using the standard retransmission mechanism. */
u8_t backoff_cnt = tcp_persist_backoff[pcb->persist_backoff-1];
if (pcb->persist_cnt < backoff_cnt) {
pcb->persist_cnt++;
}
if (pcb->persist_cnt >= backoff_cnt) {
if (tcp_zero_window_probe(pcb) == ERR_OK) {
pcb->persist_cnt = 0;
if (pcb->persist_backoff < sizeof(tcp_persist_backoff)) {
pcb->persist_backoff++;
if (pcb->persist_probe >= TCP_MAXRTX) {
++pcb_remove; /* max probes reached */
} else {
/* If snd_wnd is zero, use persist timer to send 1 byte probes
* instead of using the standard retransmission mechanism. */
u8_t backoff_cnt = tcp_persist_backoff[pcb->persist_backoff-1];
if (pcb->persist_cnt < backoff_cnt) {
pcb->persist_cnt++;
}
if (pcb->persist_cnt >= backoff_cnt) {
if (tcp_zero_window_probe(pcb) == ERR_OK) {
pcb->persist_cnt = 0;
if (pcb->persist_backoff < sizeof(tcp_persist_backoff)) {
pcb->persist_backoff++;
}
}
}
}

4
src/core/tcp_in.c
View File

@ -765,6 +765,7 @@ tcp_process(struct tcp_pcb *pcb)
pcb->tmr = tcp_ticks;
}
pcb->keep_cnt_sent = 0;
pcb->persist_probe = 0;
tcp_parseopt(pcb);
@ -1093,10 +1094,11 @@ tcp_receive(struct tcp_pcb *pcb)
/* start persist timer */
pcb->persist_cnt = 0;
pcb->persist_backoff = 1;
pcb->persist_probe = 0;
}
} else if (pcb->persist_backoff > 0) {
/* stop persist timer */
pcb->persist_backoff = 0;
pcb->persist_backoff = 0;
}
LWIP_DEBUGF(TCP_WND_DEBUG, ("tcp_receive: window update %"TCPWNDSIZE_F"\n", pcb->snd_wnd));
#if TCP_WND_DEBUG

9
src/core/tcp_out.c
View File

@ -1103,6 +1103,7 @@ tcp_output(struct tcp_pcb *pcb)
if (pcb->persist_backoff == 0) {
pcb->persist_cnt = 0;
pcb->persist_backoff = 1;
pcb->persist_probe = 0;
}
goto output_done;
}
@ -1638,6 +1639,14 @@ tcp_zero_window_probe(struct tcp_pcb *pcb)
return ERR_OK;
}
/* increment probe count. NOTE: we record probe even if it fails
to actually transmit due to an error. This ensures memory exhaustion/
routing problem doesn't leave a zero-window pcb as an indefinite zombie.
RTO mechanism has similar behavior, see pcb->nrtx */
if (pcb->persist_probe < 0xFF) {
++pcb->persist_probe;
}
is_fin = ((TCPH_FLAGS(seg->tcphdr) & TCP_FIN) != 0) && (seg->len == 0);
/* we want to send one seqno: either FIN or data (no options) */
len = is_fin ? 0 : 1;

2
src/include/lwip/tcp.h
View File

@ -310,6 +310,8 @@ struct tcp_pcb {
u8_t persist_cnt;
/* Persist timer back-off */
u8_t persist_backoff;
/* Number of persist probes */
u8_t persist_probe;
/* KEEPALIVE counter */
u8_t keep_cnt_sent;

183
test/unit/tcp/test_tcp.c
View File

@ -816,6 +816,185 @@ START_TEST(test_tcp_rto_tracking)
}
END_TEST
START_TEST(test_tcp_rto_timeout)
{
struct netif netif;
struct test_tcp_txcounters txcounters;
struct test_tcp_counters counters;
struct tcp_pcb *pcb, *cur;
err_t err;
u16_t i;
LWIP_UNUSED_ARG(_i);
/* Setup data for a single segment */
for (i = 0; i < TCP_MSS; i++) {
tx_data[i] = (u8_t)i;
}
/* initialize local vars */
test_tcp_init_netif(&netif, &txcounters, &test_local_ip, &test_netmask);
memset(&counters, 0, sizeof(counters));
/* create and initialize the pcb */
tcp_ticks = SEQNO1 - ISS;
pcb = test_tcp_new_counters_pcb(&counters);
EXPECT_RET(pcb != NULL);
tcp_set_state(pcb, ESTABLISHED, &test_local_ip, &test_remote_ip, TEST_LOCAL_PORT, TEST_REMOTE_PORT);
pcb->mss = TCP_MSS;
pcb->cwnd = TCP_MSS;
/* send our segment */
err = tcp_write(pcb, &tx_data[0], TCP_MSS, TCP_WRITE_FLAG_COPY);
EXPECT_RET(err == ERR_OK);
err = tcp_output(pcb);
EXPECT(txcounters.num_tx_calls == 1);
EXPECT(txcounters.num_tx_bytes == 1 * (TCP_MSS + 40U));
memset(&txcounters, 0, sizeof(txcounters));
/* ensure no errors have been recorded */
EXPECT(counters.err_calls == 0);
EXPECT(counters.last_err == ERR_OK);
/* Force us into retransmisson timeout */
while (!(pcb->flags & TF_RTO)) {
test_tcp_tmr();
}
/* check first rexmit */
EXPECT(pcb->nrtx == 1);
EXPECT(txcounters.num_tx_calls == 1);
EXPECT(txcounters.num_tx_bytes == 1 * (TCP_MSS + 40U));
/* still no error expected */
EXPECT(counters.err_calls == 0);
EXPECT(counters.last_err == ERR_OK);
/* keep running the timer till we hit our maximum RTO */
while (counters.last_err == ERR_OK) {
test_tcp_tmr();
}
/* check number of retransmissions */
EXPECT(txcounters.num_tx_calls == TCP_MAXRTX);
EXPECT(txcounters.num_tx_bytes == TCP_MAXRTX * (TCP_MSS + 40U));
/* check the connection (pcb) has been aborted */
EXPECT(counters.err_calls == 1);
EXPECT(counters.last_err == ERR_ABRT);
/* check our pcb is no longer active */
for (cur = tcp_active_pcbs; cur != NULL; cur = cur->next) {
EXPECT(cur != pcb);
}
EXPECT_RET(MEMP_STATS_GET(used, MEMP_TCP_PCB) == 0);
}
END_TEST
START_TEST(test_tcp_zwp_timeout)
{
struct netif netif;
struct test_tcp_txcounters txcounters;
struct test_tcp_counters counters;
struct tcp_pcb *pcb, *cur;
struct pbuf* p;
err_t err;
u16_t i;
LWIP_UNUSED_ARG(_i);
/* Setup data for two segments */
for (i = 0; i < 2*TCP_MSS; i++) {
tx_data[i] = (u8_t)i;
}
/* initialize local vars */
test_tcp_init_netif(&netif, &txcounters, &test_local_ip, &test_netmask);
memset(&counters, 0, sizeof(counters));
/* create and initialize the pcb */
tcp_ticks = SEQNO1 - ISS;
pcb = test_tcp_new_counters_pcb(&counters);
EXPECT_RET(pcb != NULL);
tcp_set_state(pcb, ESTABLISHED, &test_local_ip, &test_remote_ip, TEST_LOCAL_PORT, TEST_REMOTE_PORT);
pcb->mss = TCP_MSS;
pcb->cwnd = TCP_MSS;
/* send first segment */
err = tcp_write(pcb, &tx_data[0], TCP_MSS, TCP_WRITE_FLAG_COPY);
EXPECT(err == ERR_OK);
err = tcp_output(pcb);
EXPECT(err == ERR_OK);
/* verify segment is in-flight */
EXPECT(pcb->unsent == NULL);
check_seqnos(pcb->unacked, 1, seqnos);
EXPECT(txcounters.num_tx_calls == 1);
EXPECT(txcounters.num_tx_bytes == 1 * (TCP_MSS + 40U));
memset(&txcounters, 0, sizeof(txcounters));
/* ACK the segment and close the TX window */
p = tcp_create_rx_segment_wnd(pcb, NULL, 0, 0, TCP_MSS, TCP_ACK, 0);
test_tcp_input(p, &netif);
EXPECT(pcb->unacked == NULL);
EXPECT(pcb->unsent == NULL);
EXPECT(pcb->persist_backoff == 1);
EXPECT(pcb->snd_wnd == 0);
/* send second segment, should be buffered */
err = tcp_write(pcb, &tx_data[TCP_MSS], TCP_MSS, TCP_WRITE_FLAG_COPY);
EXPECT(err == ERR_OK);
err = tcp_output(pcb);
EXPECT(err == ERR_OK);
/* ensure it is buffered */
EXPECT(pcb->unacked == NULL);
check_seqnos(pcb->unsent, 1, &seqnos[1]);
EXPECT(txcounters.num_tx_calls == 0);
EXPECT(txcounters.num_tx_bytes == 0);
/* ensure no errors have been recorded */
EXPECT(counters.err_calls == 0);
EXPECT(counters.last_err == ERR_OK);
/* run timer till first probe */
EXPECT(pcb->persist_probe == 0);
while (pcb->persist_probe == 0) {
test_tcp_tmr();
}
EXPECT(txcounters.num_tx_calls == 1);
EXPECT(txcounters.num_tx_bytes == (1 + 40U));
memset(&txcounters, 0, sizeof(txcounters));
/* respond to probe with remote's current SEQ, ACK, and zero-window */
p = tcp_create_rx_segment_wnd(pcb, NULL, 0, 0, 0, TCP_ACK, 0);
test_tcp_input(p, &netif);
/* ensure zero-window is still active, but probe count reset */
EXPECT(pcb->persist_backoff > 1);
EXPECT(pcb->persist_probe == 0);
EXPECT(pcb->snd_wnd == 0);
/* ensure no errors have been recorded */
EXPECT(counters.err_calls == 0);
EXPECT(counters.last_err == ERR_OK);
/* now run the timer till we hit our maximum probe count */
while (counters.last_err == ERR_OK) {
test_tcp_tmr();
}
/* check maximum number of 1 byte probes were sent */
EXPECT(txcounters.num_tx_calls == TCP_MAXRTX);
EXPECT(txcounters.num_tx_bytes == TCP_MAXRTX * (1 + 40U));
/* check the connection (pcb) has been aborted */
EXPECT(counters.err_calls == 1);
EXPECT(counters.last_err == ERR_ABRT);
/* check our pcb is no longer active */
for (cur = tcp_active_pcbs; cur != NULL; cur = cur->next) {
EXPECT(cur != pcb);
}
EXPECT_RET(MEMP_STATS_GET(used, MEMP_TCP_PCB) == 0);
}
END_TEST
/** Create the suite including all tests for this module */
Suite *
tcp_suite(void)
@ -829,7 +1008,9 @@ tcp_suite(void)
TESTFUNC(test_tcp_rto_rexmit_wraparound),
TESTFUNC(test_tcp_tx_full_window_lost_from_unacked),
TESTFUNC(test_tcp_tx_full_window_lost_from_unsent),
TESTFUNC(test_tcp_rto_tracking)
TESTFUNC(test_tcp_rto_tracking),
TESTFUNC(test_tcp_rto_timeout),
TESTFUNC(test_tcp_zwp_timeout)
};
return create_suite("TCP", tests, sizeof(tests)/sizeof(testfunc), tcp_setup, tcp_teardown);
}