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tcp: advance next seq nr for zero window probes

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It is possible that the byte sent as a zero window probe is accepted
and acknowledged by the receiver side without the window being opened.
In that case, the stream has effectively advanced by one byte, and
since lwIP did not take this into account on the sender side, the
result was a desynchronization between the sender and the receiver.
That situation could occur even on a lwIP loopback device, after
filling up the receiver side's receive buffer, and resulted in an ACK
storm. This patch corrects the problem by advancing the sender's next
sequence number by one as needed when sending a zero window probe.
This commit is contained in:
David van Moolenbroek 2016-09-19 11:33:34 +00:00 committed by sg
parent 95754ba95a
commit 9ba9dee2aa
1 changed files with 7 additions and 0 deletions
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7
src/core/tcp_out.c
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@ -1537,6 +1537,7 @@ tcp_zero_window_probe(struct tcp_pcb *pcb)
struct tcp_seg *seg;
u16_t len;
u8_t is_fin;
u32_t snd_nxt;
struct netif *netif;
LWIP_DEBUGF(TCP_DEBUG, ("tcp_zero_window_probe: sending ZERO WINDOW probe to "));
@ -1581,6 +1582,12 @@ tcp_zero_window_probe(struct tcp_pcb *pcb)
pbuf_copy_partial(seg->p, d, 1, seg->p->tot_len - seg->len);
}
/* The byte may be acknowledged without the window being opened. */
snd_nxt = ntohl(seg->tcphdr->seqno) + 1;
if (TCP_SEQ_LT(pcb->snd_nxt, snd_nxt)) {
pcb->snd_nxt = snd_nxt;
}
netif = ip_route(&pcb->local_ip, &pcb->remote_ip);
if (netif == NULL) {
err = ERR_RTE;