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bug #50837: add zero-window probe timeout

Browse Source 
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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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;