busybox/networking/udhcp/packet.c
Johannes Stezenbach 2d576e2a22 udhcpc: make DHCP packets to have at least 300 DHCP bytes
Commit b8b72f02 removed all padding from DHCP packets
to fix operation with buggy servers which can't handle
maximum sized packets.  But it introduced a regression
with buggy routers which drop DHCP packets smaller
than 300 bytes (i.e. 342 byte ethernet packets).
Add back some padding to work around.

function                                             old     new   delta
udhcp_send_kernel_packet                             268     292     +24
udhcp_send_raw_packet                                462     473     +11
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 35/0)               Total: 35 bytes

Signed-off-by: Johannes Stezenbach <js@sig21.net>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2013-10-28 23:27:37 +01:00

237 lines
6.1 KiB
C

/* vi: set sw=4 ts=4: */
/*
* Packet ops
*
* Rewrite by Russ Dill <Russ.Dill@asu.edu> July 2001
*
* Licensed under GPLv2, see file LICENSE in this source tree.
*/
#include "common.h"
#include "dhcpd.h"
#include <netinet/in.h>
#include <netinet/if_ether.h>
#include <netpacket/packet.h>
void FAST_FUNC udhcp_init_header(struct dhcp_packet *packet, char type)
{
memset(packet, 0, sizeof(*packet));
packet->op = BOOTREQUEST; /* if client to a server */
switch (type) {
case DHCPOFFER:
case DHCPACK:
case DHCPNAK:
packet->op = BOOTREPLY; /* if server to client */
}
packet->htype = 1; /* ethernet */
packet->hlen = 6;
packet->cookie = htonl(DHCP_MAGIC);
if (DHCP_END != 0)
packet->options[0] = DHCP_END;
udhcp_add_simple_option(packet, DHCP_MESSAGE_TYPE, type);
}
#if defined CONFIG_UDHCP_DEBUG && CONFIG_UDHCP_DEBUG >= 2
void FAST_FUNC udhcp_dump_packet(struct dhcp_packet *packet)
{
char buf[sizeof(packet->chaddr)*2 + 1];
if (dhcp_verbose < 2)
return;
bb_info_msg(
//" op %x"
//" htype %x"
" hlen %x"
//" hops %x"
" xid %x"
//" secs %x"
//" flags %x"
" ciaddr %x"
" yiaddr %x"
" siaddr %x"
" giaddr %x"
//" chaddr %s"
//" sname %s"
//" file %s"
//" cookie %x"
//" options %s"
//, packet->op
//, packet->htype
, packet->hlen
//, packet->hops
, packet->xid
//, packet->secs
//, packet->flags
, packet->ciaddr
, packet->yiaddr
, packet->siaddr_nip
, packet->gateway_nip
//, packet->chaddr[16]
//, packet->sname[64]
//, packet->file[128]
//, packet->cookie
//, packet->options[]
);
*bin2hex(buf, (void *) packet->chaddr, sizeof(packet->chaddr)) = '\0';
bb_info_msg(" chaddr %s", buf);
}
#endif
/* Read a packet from socket fd, return -1 on read error, -2 on packet error */
int FAST_FUNC udhcp_recv_kernel_packet(struct dhcp_packet *packet, int fd)
{
int bytes;
memset(packet, 0, sizeof(*packet));
bytes = safe_read(fd, packet, sizeof(*packet));
if (bytes < 0) {
log1("Packet read error, ignoring");
return bytes; /* returns -1 */
}
if (bytes < offsetof(struct dhcp_packet, options)
|| packet->cookie != htonl(DHCP_MAGIC)
) {
bb_info_msg("Packet with bad magic, ignoring");
return -2;
}
log1("Received a packet");
udhcp_dump_packet(packet);
return bytes;
}
/* Construct a ip/udp header for a packet, send packet */
int FAST_FUNC udhcp_send_raw_packet(struct dhcp_packet *dhcp_pkt,
uint32_t source_nip, int source_port,
uint32_t dest_nip, int dest_port, const uint8_t *dest_arp,
int ifindex)
{
struct sockaddr_ll dest_sll;
struct ip_udp_dhcp_packet packet;
unsigned padding;
int fd;
int result = -1;
const char *msg;
fd = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP));
if (fd < 0) {
msg = "socket(%s)";
goto ret_msg;
}
memset(&dest_sll, 0, sizeof(dest_sll));
memset(&packet, 0, offsetof(struct ip_udp_dhcp_packet, data));
packet.data = *dhcp_pkt; /* struct copy */
dest_sll.sll_family = AF_PACKET;
dest_sll.sll_protocol = htons(ETH_P_IP);
dest_sll.sll_ifindex = ifindex;
dest_sll.sll_halen = 6;
memcpy(dest_sll.sll_addr, dest_arp, 6);
if (bind(fd, (struct sockaddr *)&dest_sll, sizeof(dest_sll)) < 0) {
msg = "bind(%s)";
goto ret_close;
}
/* We were sending full-sized DHCP packets (zero padded),
* but some badly configured servers were seen dropping them.
* Apparently they drop all DHCP packets >576 *ethernet* octets big,
* whereas they may only drop packets >576 *IP* octets big
* (which for typical Ethernet II means 590 octets: 6+6+2 + 576).
*
* In order to work with those buggy servers,
* we truncate packets after end option byte.
*
* However, RFC 1542 says "The IP Total Length and UDP Length
* must be large enough to contain the minimal BOOTP header of 300 octets".
* Thus, we retain enough padding to not go below 300 BOOTP bytes.
* Some devices have filters which drop DHCP packets shorter than that.
*/
padding = DHCP_OPTIONS_BUFSIZE - 1 - udhcp_end_option(packet.data.options);
if (padding > DHCP_SIZE - 300)
padding = DHCP_SIZE - 300;
packet.ip.protocol = IPPROTO_UDP;
packet.ip.saddr = source_nip;
packet.ip.daddr = dest_nip;
packet.udp.source = htons(source_port);
packet.udp.dest = htons(dest_port);
/* size, excluding IP header: */
packet.udp.len = htons(UDP_DHCP_SIZE - padding);
/* for UDP checksumming, ip.len is set to UDP packet len */
packet.ip.tot_len = packet.udp.len;
packet.udp.check = inet_cksum((uint16_t *)&packet,
IP_UDP_DHCP_SIZE - padding);
/* but for sending, it is set to IP packet len */
packet.ip.tot_len = htons(IP_UDP_DHCP_SIZE - padding);
packet.ip.ihl = sizeof(packet.ip) >> 2;
packet.ip.version = IPVERSION;
packet.ip.ttl = IPDEFTTL;
packet.ip.check = inet_cksum((uint16_t *)&packet.ip, sizeof(packet.ip));
udhcp_dump_packet(dhcp_pkt);
result = sendto(fd, &packet, IP_UDP_DHCP_SIZE - padding, /*flags:*/ 0,
(struct sockaddr *) &dest_sll, sizeof(dest_sll));
msg = "sendto";
ret_close:
close(fd);
if (result < 0) {
ret_msg:
bb_perror_msg(msg, "PACKET");
}
return result;
}
/* Let the kernel do all the work for packet generation */
int FAST_FUNC udhcp_send_kernel_packet(struct dhcp_packet *dhcp_pkt,
uint32_t source_nip, int source_port,
uint32_t dest_nip, int dest_port)
{
struct sockaddr_in sa;
unsigned padding;
int fd;
int result = -1;
const char *msg;
fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
if (fd < 0) {
msg = "socket(%s)";
goto ret_msg;
}
setsockopt_reuseaddr(fd);
memset(&sa, 0, sizeof(sa));
sa.sin_family = AF_INET;
sa.sin_port = htons(source_port);
sa.sin_addr.s_addr = source_nip;
if (bind(fd, (struct sockaddr *)&sa, sizeof(sa)) == -1) {
msg = "bind(%s)";
goto ret_close;
}
memset(&sa, 0, sizeof(sa));
sa.sin_family = AF_INET;
sa.sin_port = htons(dest_port);
sa.sin_addr.s_addr = dest_nip;
if (connect(fd, (struct sockaddr *)&sa, sizeof(sa)) == -1) {
msg = "connect";
goto ret_close;
}
udhcp_dump_packet(dhcp_pkt);
padding = DHCP_OPTIONS_BUFSIZE - 1 - udhcp_end_option(dhcp_pkt->options);
if (padding > DHCP_SIZE - 300)
padding = DHCP_SIZE - 300;
result = safe_write(fd, dhcp_pkt, DHCP_SIZE - padding);
msg = "write";
ret_close:
close(fd);
if (result < 0) {
ret_msg:
bb_perror_msg(msg, "UDP");
}
return result;
}