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nic_router: do not re-use ARP request as reply

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So far, in order to create an ARP reply, the NIC router merely created a copy
of the corresponding ARP request and modified only those values that differ.
This approach has the disadvantage of re-using bad parameters from a broken
request. The specific use-case that made this visible was an early version of
the Pine board network driver that used to forward ARP requests with a greater
size than required. The ARP replies of the router re-used this size and
confused other network nodes with that. In general, the NIC router should
rely on the data of incoming packets the least possible. Therefore, with this
commit, the router creates a new ARP reply from scratch and uses only those
values required from the corresponding ARP request.

Fixes #4235
This commit is contained in:
Martin Stein 2021-07-22 16:22:20 +02:00 committed by Christian Helmuth
parent 9384e075cb
commit 8bc861ca71
2 changed files with 46 additions and 28 deletions
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69
repos/os/src/server/nic_router/interface.cc
View File

@ -43,6 +43,24 @@ using Genode::Signal_transmitter;
** Utilities **
***************/
enum {
ETHERNET_HEADER_SIZE = sizeof(Ethernet_frame),
ETHERNET_DATA_SIZE_WITH_ARP =
sizeof(Arp_packet) + ETHERNET_HEADER_SIZE < Ethernet_frame::MIN_SIZE ?
Ethernet_frame::MIN_SIZE - ETHERNET_HEADER_SIZE :
sizeof(Arp_packet),
ETHERNET_CRC_SIZE = sizeof(Genode::uint32_t),
ARP_PACKET_SIZE =
ETHERNET_HEADER_SIZE +
ETHERNET_DATA_SIZE_WITH_ARP +
ETHERNET_CRC_SIZE,
};
template <typename LINK_TYPE>
static void _destroy_dissolved_links(Link_list &dissolved_links,
Deallocator &dealloc)
@ -1265,15 +1283,7 @@ void Interface::_handle_ip(Ethernet_frame &eth,
void Interface::_broadcast_arp_request(Ipv4_address const &src_ip,
Ipv4_address const &dst_ip)
{
enum {
ETH_HDR_SZ = sizeof(Ethernet_frame),
ETH_DAT_SZ = sizeof(Arp_packet) + ETH_HDR_SZ >= Ethernet_frame::MIN_SIZE ?
sizeof(Arp_packet) :
Ethernet_frame::MIN_SIZE - ETH_HDR_SZ,
ETH_CRC_SZ = sizeof(Genode::uint32_t),
PKT_SIZE = ETH_HDR_SZ + ETH_DAT_SZ + ETH_CRC_SZ,
};
send(PKT_SIZE, [&] (void *pkt_base, Size_guard &size_guard) {
send(ARP_PACKET_SIZE, [&] (void *pkt_base, Size_guard &size_guard) {
/* write Ethernet header */
Ethernet_frame &eth = Ethernet_frame::construct_at(pkt_base, size_guard);
@ -1340,22 +1350,31 @@ void Interface::_handle_arp_reply(Ethernet_frame &eth,
}
void Interface::_send_arp_reply(Ethernet_frame &eth,
Size_guard &size_guard,
Arp_packet &arp)
void Interface::_send_arp_reply(Ethernet_frame &request_eth,
Arp_packet &request_arp)
{
/* interchange source and destination MAC and IP addresses */
Ipv4_address dst_ip = arp.dst_ip();
arp.dst_ip(arp.src_ip());
arp.dst_mac(arp.src_mac());
eth.dst(eth.src());
arp.src_ip(dst_ip);
arp.src_mac(_router_mac);
eth.src(_router_mac);
send(ARP_PACKET_SIZE, [&] (void *reply_base, Size_guard &reply_guard) {
/* mark packet as reply and send it back to its sender */
arp.opcode(Arp_packet::REPLY);
send(eth, size_guard);
Ethernet_frame &reply_eth {
Ethernet_frame::construct_at(reply_base, reply_guard) };
reply_eth.dst(request_eth.src());
reply_eth.src(_router_mac);
reply_eth.type(Ethernet_frame::Type::ARP);
Arp_packet &reply_arp {
reply_eth.construct_at_data<Arp_packet>(reply_guard) };
reply_arp.hardware_address_type(Arp_packet::ETHERNET);
reply_arp.protocol_address_type(Arp_packet::IPV4);
reply_arp.hardware_address_size(sizeof(Mac_address));
reply_arp.protocol_address_size(sizeof(Ipv4_address));
reply_arp.opcode(Arp_packet::REPLY);
reply_arp.src_mac(_router_mac);
reply_arp.src_ip(request_arp.dst_ip());
reply_arp.dst_mac(request_arp.src_mac());
reply_arp.dst_ip(request_arp.src_ip());
});
}
@ -1380,7 +1399,7 @@ void Interface::_handle_arp_request(Ethernet_frame &eth,
if (_config().verbose()) {
log("[", local_domain, "] answer ARP request for router IP "
"with router MAC"); }
_send_arp_reply(eth, size_guard, arp);
_send_arp_reply(eth, arp);
} else {
@ -1405,7 +1424,7 @@ void Interface::_handle_arp_request(Ethernet_frame &eth,
if (_config().verbose()) {
log("[", local_domain, "] answer ARP request for foreign IP "
"with router MAC"); }
_send_arp_reply(eth, size_guard, arp);
_send_arp_reply(eth, arp);
}
}
}

5
repos/os/src/server/nic_router/interface.h
View File

@ -217,9 +217,8 @@ class Net::Interface : private Interface_list::Element
Arp_packet &arp,
Domain &local_domain);
void _send_arp_reply(Ethernet_frame &eth,
Size_guard &size_guard,
Arp_packet &arp);
void _send_arp_reply(Ethernet_frame &request_eth,
Arp_packet &request_arp);
void _handle_dhcp_request(Ethernet_frame &eth,
Dhcp_packet &dhcp,