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handle ACK in FIN, fix ACK to FIN + payload

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This commit is contained in:
Sergio R. Caprile 2026-08-07 11:49:28 -03:00
parent 9f16806a22
commit 9c6b4edd37
3 changed files with 99 additions and 30 deletions
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34
mongoose.c
View file

@ -9693,6 +9693,8 @@ static void read_conn(struct mg_connection *c, struct pkt *pkt) {
struct connstate *s = (struct connstate *) (c + 1);
struct mg_iobuf *io = c->is_tls ? &c->rtls : &c->recv;
uint32_t seq = mg_ntohl(pkt->tcp->seq);
// Evaluation order is important: 1) process FIN, 2) process keep-alive,
// 3) discard invalid SEG.SEQ, 4) process ACK and payload.
if (pkt->tcp->flags & TH_FIN) {
uint8_t flags = TH_ACK;
if (mg_ntohl(pkt->tcp->seq) != s->ack) {
@ -9721,18 +9723,12 @@ static void read_conn(struct mg_connection *c, struct pkt *pkt) {
}
tx_tcp(c->mgr->ifp, s->mac, &c->loc, &c->rem, c->dscp, flags,
mg_htonl(s->seq), mg_htonl(s->ack), "", 0);
if (pkt->pay.len == 0) return; // if no data, we're done
} else if (pkt->pay.len <= 1 && mg_ntohl(pkt->tcp->seq) == s->ack - 1) {
// Keep-Alive (RFC-9293 3.8.4, allow erroneous implementations)
MG_VERBOSE(("%lu keepalive ACK", c->id));
tx_tcp(c->mgr->ifp, s->mac, &c->loc, &c->rem, c->dscp, TH_ACK,
mg_htonl(s->seq), mg_htonl(s->ack), NULL, 0);
return; // no data to process
} else if (pkt->pay.len == 0) { // this is an ACK
if (pkt->tcp->flags & TH_ACK)
handle_ack(s, mg_ntohl(pkt->tcp->ack), mg_ntohs(pkt->tcp->win));
if (s->fin_rcvd && s->ttype == MIP_TTYPE_FIN) s->twclosure = true;
return; // no data to process
return; // RFC-9293 3.10.7.4 discard (incorrect) payload, ACK, window
} else if (seq != s->ack) {
uint32_t ack = (uint32_t) (mg_htonl(pkt->tcp->seq) + pkt->pay.len);
if (s->ack == ack) {
@ -9742,14 +9738,20 @@ static void read_conn(struct mg_connection *c, struct pkt *pkt) {
tx_tcp(c->mgr->ifp, s->mac, &c->loc, &c->rem, c->dscp, TH_ACK,
mg_htonl(s->seq), mg_htonl(s->ack), "", 0);
}
return; // drop it
} else if (io->size - io->len < pkt->pay.len &&
!mg_iobuf_resize(io, io->len + pkt->pay.len)) {
return; // drop it, RFC-9293 3.10.7.4: ignore ACKno
}
// Now process the segment for ACK and payload
if (pkt->tcp->flags & TH_ACK) {
handle_ack(s, mg_ntohl(pkt->tcp->ack), mg_ntohs(pkt->tcp->win));
if (pkt->pay.len == 0 && s->fin_rcvd && s->ttype == MIP_TTYPE_FIN)
s->twclosure = true;
}
if (pkt->pay.len == 0) return;
if (io->size - io->len < pkt->pay.len &&
!mg_iobuf_resize(io, io->len + pkt->pay.len)) {
mg_error(c, "oom");
return; // drop it
}
if (pkt->tcp->flags & TH_ACK)
handle_ack(s, mg_ntohl(pkt->tcp->ack), mg_ntohs(pkt->tcp->win));
// Copy TCP payload into the IO buffer. If the connection is plain text,
// we copy to c->recv. If the connection is TLS, this data is encrypted,
// therefore we copy that encrypted data to the c->rtls iobuffer instead,
@ -9758,9 +9760,11 @@ static void read_conn(struct mg_connection *c, struct pkt *pkt) {
memcpy(&io->buf[io->len], pkt->pay.buf, pkt->pay.len);
io->len += pkt->pay.len;
MG_VERBOSE(("%lu SEQ %x -> %x", c->id, mg_htonl(pkt->tcp->seq), s->ack));
// Advance ACK counter
s->ack = (uint32_t) (mg_htonl(pkt->tcp->seq) + pkt->pay.len);
s->unacked += pkt->pay.len;
if (!(pkt->tcp->flags & TH_FIN)) { // FIN already advanced s->ack
// Advance ACK counter
s->ack = (uint32_t) (mg_htonl(pkt->tcp->seq) + pkt->pay.len);
s->unacked += pkt->pay.len;
}
// size_t diff = s->acked <= s->ack ? s->ack - s->acked : s->ack;
if (s->unacked > MG_TCPIP_WIN / 2 && s->acked != s->ack) {
// Send ACK immediately

34
src/net_builtin.c
View file

@ -1462,6 +1462,8 @@ static void read_conn(struct mg_connection *c, struct pkt *pkt) {
struct connstate *s = (struct connstate *) (c + 1);
struct mg_iobuf *io = c->is_tls ? &c->rtls : &c->recv;
uint32_t seq = mg_ntohl(pkt->tcp->seq);
// Evaluation order is important: 1) process FIN, 2) process keep-alive,
// 3) discard invalid SEG.SEQ, 4) process ACK and payload.
if (pkt->tcp->flags & TH_FIN) {
uint8_t flags = TH_ACK;
if (mg_ntohl(pkt->tcp->seq) != s->ack) {
@ -1490,18 +1492,12 @@ static void read_conn(struct mg_connection *c, struct pkt *pkt) {
}
tx_tcp(c->mgr->ifp, s->mac, &c->loc, &c->rem, c->dscp, flags,
mg_htonl(s->seq), mg_htonl(s->ack), "", 0);
if (pkt->pay.len == 0) return; // if no data, we're done
} else if (pkt->pay.len <= 1 && mg_ntohl(pkt->tcp->seq) == s->ack - 1) {
// Keep-Alive (RFC-9293 3.8.4, allow erroneous implementations)
MG_VERBOSE(("%lu keepalive ACK", c->id));
tx_tcp(c->mgr->ifp, s->mac, &c->loc, &c->rem, c->dscp, TH_ACK,
mg_htonl(s->seq), mg_htonl(s->ack), NULL, 0);
return; // no data to process
} else if (pkt->pay.len == 0) { // this is an ACK
if (pkt->tcp->flags & TH_ACK)
handle_ack(s, mg_ntohl(pkt->tcp->ack), mg_ntohs(pkt->tcp->win));
if (s->fin_rcvd && s->ttype == MIP_TTYPE_FIN) s->twclosure = true;
return; // no data to process
return; // RFC-9293 3.10.7.4 discard (incorrect) payload, ACK, window
} else if (seq != s->ack) {
uint32_t ack = (uint32_t) (mg_htonl(pkt->tcp->seq) + pkt->pay.len);
if (s->ack == ack) {
@ -1511,14 +1507,20 @@ static void read_conn(struct mg_connection *c, struct pkt *pkt) {
tx_tcp(c->mgr->ifp, s->mac, &c->loc, &c->rem, c->dscp, TH_ACK,
mg_htonl(s->seq), mg_htonl(s->ack), "", 0);
}
return; // drop it
} else if (io->size - io->len < pkt->pay.len &&
!mg_iobuf_resize(io, io->len + pkt->pay.len)) {
return; // drop it, RFC-9293 3.10.7.4: ignore ACKno
}
// Now process the segment for ACK and payload
if (pkt->tcp->flags & TH_ACK) {
handle_ack(s, mg_ntohl(pkt->tcp->ack), mg_ntohs(pkt->tcp->win));
if (pkt->pay.len == 0 && s->fin_rcvd && s->ttype == MIP_TTYPE_FIN)
s->twclosure = true;
}
if (pkt->pay.len == 0) return;
if (io->size - io->len < pkt->pay.len &&
!mg_iobuf_resize(io, io->len + pkt->pay.len)) {
mg_error(c, "oom");
return; // drop it
}
if (pkt->tcp->flags & TH_ACK)
handle_ack(s, mg_ntohl(pkt->tcp->ack), mg_ntohs(pkt->tcp->win));
// Copy TCP payload into the IO buffer. If the connection is plain text,
// we copy to c->recv. If the connection is TLS, this data is encrypted,
// therefore we copy that encrypted data to the c->rtls iobuffer instead,
@ -1527,9 +1529,11 @@ static void read_conn(struct mg_connection *c, struct pkt *pkt) {
memcpy(&io->buf[io->len], pkt->pay.buf, pkt->pay.len);
io->len += pkt->pay.len;
MG_VERBOSE(("%lu SEQ %x -> %x", c->id, mg_htonl(pkt->tcp->seq), s->ack));
// Advance ACK counter
s->ack = (uint32_t) (mg_htonl(pkt->tcp->seq) + pkt->pay.len);
s->unacked += pkt->pay.len;
if (!(pkt->tcp->flags & TH_FIN)) { // FIN already advanced s->ack
// Advance ACK counter
s->ack = (uint32_t) (mg_htonl(pkt->tcp->seq) + pkt->pay.len);
s->unacked += pkt->pay.len;
}
// size_t diff = s->acked <= s->ack ? s->ack - s->acked : s->ack;
if (s->unacked > MG_TCPIP_WIN / 2 && s->acked != s->ack) {
// Send ACK immediately

61
test/mip_test.c
View file

@ -536,6 +536,23 @@ static void test_tcp_basics(bool ipv6) {
s_driver_data.len = 0;
mg_mgr_free(&mgr);
// Initiate closure with FIN and payload
init_tcp_tests(&mgr, &e, &ipp, &driver, &mif, fn);
init_tcp_handshake(&e, &ipp, &mgr); // starts with seq_no=1000, ackno=2
create_tcp_simpleseg(&e, &ipp, 1001, 2, TH_FIN | TH_ACK, 2);
mg_mgr_poll(&mgr, 0);
while (!received_response(&s_driver_data)) mg_mgr_poll(&mgr, 0);
ASSERT((t->flags == (TH_FIN | TH_ACK)));
ASSERT((t->seq == mg_htonl(2)));
ASSERT((t->ack == mg_htonl(1004)));
create_tcp_simpleseg(&e, &ipp, 1004, 3, TH_ACK, 0);
mg_mgr_poll(&mgr, 0);
ASSERT(!received_response(&s_driver_data));
ASSERT(mgr.conns->next == NULL); // only one connection: the listener
s_driver_data.len = 0;
mg_mgr_free(&mgr);
// Test client-initiated closure timeout, do not ACK
init_tcp_tests(&mgr, &e, &ipp, &driver, &mif, fn);
init_tcp_handshake(&e, &ipp, &mgr); // starts with seq_no=1000, ackno=2
@ -964,6 +981,49 @@ static void test_tcp_txwindow(void) {
mg_mgr_free(&mgr);
}
static void test_tcp_ackseq(void) {
struct mg_mgr mgr;
struct eth e;
struct ip ip;
struct ipp ipp;
struct tcp *t = (struct tcp *) (s_driver_data.buf + sizeof(e) + sizeof(ip));
int count = 0, stallcount;
uint32_t seq;
struct mg_tcpip_driver driver;
struct mg_tcpip_if mif;
ipp.ip4 = &ip;
ipp.ip6 = NULL;
init_tcp_tests(&mgr, &e, &ipp, &driver, &mif, txwindow_fn);
mgr.conns->fn_data = &count;
init_tcp_handshake(&e, &ipp, &mgr);
do {
while (!received_response(&s_driver_data)) mg_mgr_poll(&mgr, 0);
seq = (uint32_t)(mg_htonl(t->seq) + s_driver_data.len - (size_t)((char *)((uint32_t *)t + (t->off >> 4)) - s_driver_data.buf));
} while (seq < (TCP_TEST_WIN + 2));
stallcount = count;
mg_mgr_poll(&mgr, 0), s_driver_data.len = 0;
ASSERT(stallcount == count);
// Keepalive probe
create_tcp_simpleseg(&e, &ipp, 1000, seq, TH_ACK, 0);
mg_mgr_poll(&mgr, 0);
ASSERT(stallcount == count);
// Invalid SEG.SEQ
create_tcp_simpleseg(&e, &ipp, 1002, seq, TH_ACK, 0);
mg_mgr_poll(&mgr, 0);
ASSERT(stallcount == count);
// Valid FIN+ACK
create_tcp_simpleseg(&e, &ipp, 1001, seq, TH_FIN | TH_ACK, 0);
mg_mgr_poll(&mgr, 0);
ASSERT(stallcount < count);
s_driver_data.len = 0;
mg_mgr_free(&mgr);
}
static void test_frag_recv_path(void) {
struct mg_mgr mgr;
struct eth e;
@ -1125,6 +1185,7 @@ static void test_tcp(bool ipv6) {
test_tcp_backlog();
test_tcp_retransmit();
test_tcp_txwindow();
test_tcp_ackseq();
}
}