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Kernel: Send RST/ACK if no socket is available

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Previously there was no way for Serenity to send a packet without an
established socket connection, and there was no way to appropriately
respond to a SYN packet on a non-listening port. This patch will respond
to any non-established socket attempts with the appropraite RST/ACK,
letting the client know to close the connection.
This commit is contained in:
brapru 2021-07-18 18:19:25 -04:00 • committed by Gunnar Beutner
parent 63a15ed19d
commit 9c3e6f3f63
2 changed files with 38 additions and 16 deletions
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50
Kernel/Net/NetworkTask.cpp
View file

@ -30,6 +30,7 @@ static void handle_icmp(EthernetFrameHeader const&, IPv4Packet const&, Time cons
static void handle_udp(IPv4Packet const&, Time const& packet_timestamp);
static void handle_tcp(IPv4Packet const&, Time const& packet_timestamp);
static void send_delayed_tcp_ack(RefPtr<TCPSocket> socket);
static void send_tcp_rst(IPv4Packet const& ipv4_packet, TCPPacket const& tcp_packet, RefPtr<NetworkAdapter> adapter);
static void flush_delayed_tcp_acks();
static void retransmit_tcp_packets();
@ -328,6 +329,39 @@ void flush_delayed_tcp_acks()
}
}
void send_tcp_rst(IPv4Packet const& ipv4_packet, TCPPacket const& tcp_packet, RefPtr<NetworkAdapter> adapter)
{
auto routing_decision = route_to(ipv4_packet.source(), ipv4_packet.destination(), adapter);
if (routing_decision.is_zero())
return;
auto ipv4_payload_offset = routing_decision.adapter->ipv4_payload_offset();
const size_t options_size = 0;
const size_t tcp_header_size = sizeof(TCPPacket) + options_size;
const size_t buffer_size = ipv4_payload_offset + tcp_header_size;
auto packet = routing_decision.adapter->acquire_packet_buffer(buffer_size);
if (!packet)
return;
routing_decision.adapter->fill_in_ipv4_header(*packet, ipv4_packet.destination(),
routing_decision.next_hop, ipv4_packet.source(), IPv4Protocol::TCP,
buffer_size - ipv4_payload_offset, 64);
memset(packet->buffer.data() + ipv4_payload_offset, 0, sizeof(TCPPacket));
auto& rst_packet = *(TCPPacket*)(packet->buffer.data() + ipv4_payload_offset);
rst_packet.set_source_port(tcp_packet.destination_port());
rst_packet.set_destination_port(tcp_packet.source_port());
rst_packet.set_window_size(0);
rst_packet.set_sequence_number(0);
rst_packet.set_ack_number(tcp_packet.sequence_number() + 1);
rst_packet.set_data_offset(tcp_header_size / sizeof(u32));
rst_packet.set_flags(TCPFlags::RST | TCPFlags::ACK);
rst_packet.set_checksum(TCPSocket::compute_tcp_checksum(ipv4_packet.source(), ipv4_packet.destination(), rst_packet, 0));
routing_decision.adapter->send_packet({ packet->buffer.data(), packet->buffer.size() });
routing_decision.adapter->release_packet_buffer(*packet);
}
void handle_tcp(IPv4Packet const& ipv4_packet, Time const& packet_timestamp)
{
if (ipv4_packet.payload_size() < sizeof(TCPPacket)) {
@ -377,20 +411,8 @@ void handle_tcp(IPv4Packet const& ipv4_packet, Time const& packet_timestamp)
auto socket = TCPSocket::from_tuple(tuple);
if (!socket) {
dbgln("handle_tcp: No TCP socket for tuple {}", tuple.to_string());
dbgln("handle_tcp: source={}:{}, destination={}:{}, seq_no={}, ack_no={}, flags={:#04x} ({}{}{}{}), window_size={}, payload_size={}",
ipv4_packet.source().to_string(), tcp_packet.source_port(),
ipv4_packet.destination().to_string(),
tcp_packet.destination_port(),
tcp_packet.sequence_number(),
tcp_packet.ack_number(),
tcp_packet.flags(),
tcp_packet.has_syn() ? "SYN " : "",
tcp_packet.has_ack() ? "ACK " : "",
tcp_packet.has_fin() ? "FIN " : "",
tcp_packet.has_rst() ? "RST " : "",
tcp_packet.window_size(),
payload_size);
dbgln("handle_tcp: No TCP socket for tuple {}. Sending RST.", tuple.to_string());
send_tcp_rst(ipv4_packet, tcp_packet, adapter);
return;
}