udhcpd: optional BOOTP support

from Adam Goldman <adamg@pobox.com>

This patch makes udhcpd respond correctly to queries from BOOTP clients.

It contains the following changes:

The end field, or DHCP_END option, is required in DHCP requests but
optional in BOOTP requests. However, we still send an end
field in all replies, because some BOOTP clients expect one in replies
even if they didn't send one in the request.

Requests without a DHCP_MESSAGE_TYPE are recognized as BOOTP requests
and handled appropriately, instead of being discarded. We still require
an RFC 1048 options field, but we allow it to be empty.

Since a BOOTP client will keep using the assigned IP forever, we only
send a BOOTP reply if a static lease exists for that client.

BOOTP replies shouldn't contain DHCP_* options, so we omit them if there
was no DHCP_MESSAGE_TYPE in the request. Options other than DHCP_*
options are still sent.

The options field of a BOOTP reply must be exactly 64 bytes. If we
construct a reply with more than 64 bytes of options, we give up and log
an error instead of sending it. udhcp_send_raw_packet already pads the
options field to 64 bytes if it is too short.

This implementation has been tested against an HP PA-RISC client.

function                                             old     new   delta
.rodata                                           105247  105321     +74
udhcpd_main                                         1520    1591     +71
send_offer                                           419     470     +51
init_packet                                           81      97     +16
udhcp_init_header                                     75      88     +13
udhcp_scan_options                                   192     203     +11
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 6/0 up/down: 236/0)             Total: 236 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/networking/udhcp/dhcpc.c b/networking/udhcp/dhcpc.c
index c757fb37c..200a2fb8a 100644
--- a/networking/udhcp/dhcpc.c
+++ b/networking/udhcp/dhcpc.c
@@ -971,7 +971,7 @@ static NOINLINE int d4_recv_raw_packet(struct dhcp_packet *dhcp_pkt, int fd)
 	}
  skip_udp_sum_check:
 
-	if (packet.data.cookie != htonl(DHCP_MAGIC)) {
+	if (packet.data.cookie != htonl(RFC1048_MAGIC)) {
 		log1s("packet with bad magic, ignoring");
 		return -2;
 	}