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n-dhcp4: don't fail dispatch in case of receive errors

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Currently any error encountered in n_dhcp4_c_connection_dispatch_io()
causes a dispatch failure and interrupts the library state
machine. The recvmsg() on the socket can fail for different reasons;
one of these is for example that the UDP request previously sent got a
ICMP port-unreachable response. This can be reproduced in the
following way:

 ip netns add ns1
 ip link add veth0 type veth peer name veth1
 ip link set veth1 netns ns1
 ip link set veth0 up

 cat > dhcpd.conf <<EOF
 server-identifier 172.25.0.1;
 max-lease-time 120;
 default-lease-time 120;
 subnet 172.25.0.0 netmask 255.255.255.0 {
        range 172.25.0.100 172.25.0.200;
 }
 EOF

 ip -n ns1 link set veth1 up
 ip -n ns1 address add dev veth1 172.25.0.1/24
 ip netns exec ns1 iptables -A INPUT -p udp --dport 67 -j REJECT
 ip netns exec ns1 dhcpd -4 -cf dhcpd.conf -pf /tmp/dhcp-server.pid

If a client is started on veth0, it is able to obtain a lease despite
the firewall rule blocking DHCP, because dhcpd uses a packet
socket. Then it fails during the renewal because the recvmsg() fails:

 dhcp4 (veth0): send REQUEST of 172.25.0.178 to 172.25.0.1
 dhcp4 (veth0): error -111 dispatching events
 dhcp4 (veth0): state changed bound -> fail

The client should consider such errors non fatal and keep running.

https://bugzilla.redhat.com/show_bug.cgi?id=1829178
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/486
(cherry picked from commit c5d1d4c498)
This commit is contained in:
Beniamino Galvani 2020-04-29 18:18:28 +02:00
parent 39a8dd0dc8
commit bee01292f8
2 changed files with 22 additions and 8 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

29
shared/n-dhcp4/src/n-dhcp4-c-connection.c
View file

@ -1136,6 +1136,13 @@ int n_dhcp4_c_connection_dispatch_timer(NDhcp4CConnection *connection,
return 0;
}
/*
* Returns:
* 0 on success
* N_DHCP4_E_MALFORMED if a malformed packet was received
* N_DHCP4_E_UNEXPECTED if the packet received contains unexpected data
* N_DHCP4_E_AGAIN if there was another error (non fatal for the client)
*/
int n_dhcp4_c_connection_dispatch_io(NDhcp4CConnection *connection,
NDhcp4Incoming **messagep) {
_c_cleanup_(n_dhcp4_incoming_freep) NDhcp4Incoming *message = NULL;
@ -1150,10 +1157,11 @@ int n_dhcp4_c_connection_dispatch_io(NDhcp4CConnection *connection,
connection->scratch_buffer,
sizeof(connection->scratch_buffer),
&message);
if (r)
if (!r)
break;
else if (r == N_DHCP4_E_MALFORMED)
return r;
break;
return N_DHCP4_E_AGAIN;
case N_DHCP4_C_CONNECTION_STATE_DRAINING:
r = n_dhcp4_c_socket_packet_recv(connection->fd_packet,
connection->scratch_buffer,
@ -1161,8 +1169,10 @@ int n_dhcp4_c_connection_dispatch_io(NDhcp4CConnection *connection,
&message);
if (!r)
break;
else if (r != N_DHCP4_E_AGAIN)
else if (r == N_DHCP4_E_MALFORMED)
return r;
else if (r != N_DHCP4_E_AGAIN)
return N_DHCP4_E_AGAIN;
/*
* The UDP socket is open and the packet socket has been shut down
@ -1180,18 +1190,21 @@ int n_dhcp4_c_connection_dispatch_io(NDhcp4CConnection *connection,
connection->scratch_buffer,
sizeof(connection->scratch_buffer),
&message);
if (r)
if (!r)
break;
else if (r == N_DHCP4_E_MALFORMED)
return r;
break;
return N_DHCP4_E_AGAIN;
default:
abort();
return -ENOTRECOVERABLE;
}
r = n_dhcp4_c_connection_verify_incoming(connection, message, &type);
if (r)
if (r == N_DHCP4_E_MALFORMED || r == N_DHCP4_E_UNEXPECTED)
return r;
else if (r != 0)
return N_DHCP4_E_AGAIN;
if (type == N_DHCP4_MESSAGE_OFFER || type == N_DHCP4_MESSAGE_ACK) {
n_dhcp4_c_log(connection->client_config, LOG_INFO,

1
shared/n-dhcp4/src/n-dhcp4-c-probe.c
View file

@ -1242,6 +1242,7 @@ int n_dhcp4_client_probe_dispatch_io(NDhcp4ClientProbe *probe, uint32_t events)
return 0;
}
abort();
return r;
}