diff options
| -rw-r--r-- | networking/udhcp/packet.c | 32 |
1 files changed, 20 insertions, 12 deletions
diff --git a/networking/udhcp/packet.c b/networking/udhcp/packet.c index c01fb7d..4badc9c 100644 --- a/networking/udhcp/packet.c +++ b/networking/udhcp/packet.c @@ -173,6 +173,7 @@ int FAST_FUNC udhcp_send_raw_packet(struct dhcp_packet *dhcp_pkt, { struct sockaddr_ll dest_sll; struct ip_udp_dhcp_packet packet; + unsigned padding; int fd; int result = -1; const char *msg; @@ -198,34 +199,40 @@ int FAST_FUNC udhcp_send_raw_packet(struct dhcp_packet *dhcp_pkt, 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. + */ + padding = DHCP_OPTIONS_BUFSIZE - 1 - udhcp_end_option(packet.data.options); + 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(UPD_DHCP_SIZE); + packet.udp.len = htons(UPD_DHCP_SIZE - padding); /* for UDP checksumming, ip.len is set to UDP packet len */ packet.ip.tot_len = packet.udp.len; - packet.udp.check = udhcp_checksum(&packet, IP_UPD_DHCP_SIZE); + packet.udp.check = udhcp_checksum(&packet, IP_UPD_DHCP_SIZE - padding); /* but for sending, it is set to IP packet len */ - packet.ip.tot_len = htons(IP_UPD_DHCP_SIZE); + packet.ip.tot_len = htons(IP_UPD_DHCP_SIZE - padding); packet.ip.ihl = sizeof(packet.ip) >> 2; packet.ip.version = IPVERSION; packet.ip.ttl = IPDEFTTL; packet.ip.check = udhcp_checksum(&packet.ip, sizeof(packet.ip)); - /* Currently we send full-sized DHCP packets (zero padded). - * If you need to change this: last byte of the packet is - * packet.data.options[udhcp_end_option(packet.data.options)] - */ udhcp_dump_packet(dhcp_pkt); - result = sendto(fd, &packet, IP_UPD_DHCP_SIZE, 0, + result = sendto(fd, &packet, IP_UPD_DHCP_SIZE - padding, /*flags:*/ 0, (struct sockaddr *) &dest_sll, sizeof(dest_sll)); msg = "sendto"; ret_close: close(fd); - /* FIXME: and if result >= 0 but != IP_UPD_DHCP_SIZE? */ if (result < 0) { ret_msg: bb_perror_msg(msg, "PACKET"); @@ -239,6 +246,7 @@ int FAST_FUNC udhcp_send_kernel_packet(struct dhcp_packet *dhcp_pkt, uint32_t dest_nip, int dest_port) { struct sockaddr_in client; + unsigned padding; int fd; int result = -1; const char *msg; @@ -268,13 +276,13 @@ int FAST_FUNC udhcp_send_kernel_packet(struct dhcp_packet *dhcp_pkt, goto ret_close; } - /* Currently we send full-sized DHCP packets (see above) */ udhcp_dump_packet(dhcp_pkt); - result = safe_write(fd, dhcp_pkt, DHCP_SIZE); + + padding = DHCP_OPTIONS_BUFSIZE - 1 - udhcp_end_option(dhcp_pkt->options); + result = safe_write(fd, dhcp_pkt, DHCP_SIZE - padding); msg = "write"; ret_close: close(fd); - /* FIXME: and if result >= 0 but != DHCP_SIZE? */ if (result < 0) { ret_msg: bb_perror_msg(msg, "UDP"); |