b8b72f02f
Denys Vlasenko
2010-05-31
Subject
dhcp: truncate packets instead of padding them to 574 bytes. closes bug 1849
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Commit Diff GitHub →
networking/udhcp/packet.c+20 -12
| @@ -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"); | |