From 6191a07eb328558bc4381dcb5bbc3e0b6a71908a Mon Sep 17 00:00:00 2001 From: "Nicholas J. Kain" Date: Sat, 11 Jun 2011 11:05:53 -0400 Subject: [PATCH] Move get_raw_packet() to packet.c and make get_packet() and get_raw_packet() static functions. --- ndhc/dhcpmsg.h | 3 +- ndhc/packet.c | 76 ++++++++++++++++++++++++++++++++++++++++++++++++-- ndhc/packet.h | 3 +- 3 files changed, 75 insertions(+), 7 deletions(-) diff --git a/ndhc/dhcpmsg.h b/ndhc/dhcpmsg.h index 7bacd7b..d2c2e47 100644 --- a/ndhc/dhcpmsg.h +++ b/ndhc/dhcpmsg.h @@ -1,5 +1,5 @@ /* dhcpmsg.c - dhcp packet generation and sending functions - * Time-stamp: <2011-03-31 03:27:02 nk> + * Time-stamp: <2011-06-11 11:03:22 njk> * * (c) 2004-2011 Nicholas J. Kain * (c) 2001 Russ Dill @@ -46,6 +46,5 @@ int send_selecting(uint32_t xid, uint32_t server, uint32_t requested); int send_renew(uint32_t xid, uint32_t server, uint32_t ciaddr); int send_decline(uint32_t xid, uint32_t server, uint32_t requested); int send_release(uint32_t server, uint32_t ciaddr); -int get_raw_packet(struct dhcpMessage *payload, int fd); #endif diff --git a/ndhc/packet.c b/ndhc/packet.c index 14401ee..0e0a892 100644 --- a/ndhc/packet.c +++ b/ndhc/packet.c @@ -1,5 +1,5 @@ /* packet.c - send and react to DHCP message packets - * Time-stamp: <2011-06-11 10:58:37 njk> + * Time-stamp: <2011-06-11 11:03:05 njk> * * (c) 2004-2011 Nicholas J. Kain * (c) 2001 Russ Dill @@ -40,8 +40,9 @@ #include "io.h" #include "options.h" -/* Read a packet from socket fd, return -1 on read error, -2 on packet error */ -int get_packet(struct dhcpMessage *packet, int fd) +// Read a packet from a cooked socket. Returns -1 on fatal error, -2 on +// transient error. +static int get_packet(struct dhcpMessage *packet, int fd) { int bytes; @@ -59,6 +60,75 @@ int get_packet(struct dhcpMessage *packet, int fd) return bytes; } +// Read a packet from a raw socket. Returns -1 on fatal error, -2 on +// transient error. +static int get_raw_packet(struct dhcpMessage *payload, int fd) +{ + struct ip_udp_dhcp_packet packet; + uint16_t check; + + memset(&packet, 0, IP_UPD_DHCP_SIZE); + int len = safe_read(fd, (char *)&packet, IP_UPD_DHCP_SIZE); + if (len == -1) { + if (errno == EAGAIN || errno == EWOULDBLOCK) + return -2; + log_line("get_raw_packet: read error %s", strerror(errno)); + return -1; + } + + /* ignore any extra garbage bytes */ + len = ntohs(packet.ip.tot_len); + + // Validate the IP and UDP headers. + if (packet.ip.protocol != IPPROTO_UDP) { + log_line("IP header is not UDP: %d", packet.ip.protocol); + return -2; + } + if (packet.ip.version != IPVERSION) { + log_line("IP version is not IPv4"); + return -2; + } + if (packet.ip.ihl != sizeof packet.ip >> 2) { + log_line("IP header length incorrect"); + return -2; + } + check = packet.ip.check; + packet.ip.check = 0; + if (check != checksum(&packet.ip, sizeof packet.ip)) { + log_line("IP header checksum incorrect"); + return -2; + } + if (packet.udp.dest != htons(DHCP_CLIENT_PORT)) { + log_line("UDP destination port incorrect: %d", ntohs(packet.udp.dest)); + return -2; + } + if (len > IP_UPD_DHCP_SIZE) { + log_line("Data longer than that of a IP+UDP+DHCP message: %d", len); + return -2; + } + if (ntohs(packet.udp.len) != (short)(len - sizeof packet.ip)) { + log_line("UDP header length incorrect"); + return -2; + } + + /* verify the UDP checksum by replacing the header with a psuedo header */ + memset(&packet.ip, 0, offsetof(struct iphdr, protocol)); + /* preserved fields: protocol, check, saddr, daddr */ + packet.ip.tot_len = packet.udp.len; /* cheat on the psuedo-header */ + check = packet.udp.check; + packet.udp.check = 0; + if (check && check != checksum(&packet, len)) { + log_error("Packet with bad UDP checksum received, ignoring"); + return -2; + } + + memcpy(payload, &packet.data, + len - sizeof packet.ip - sizeof packet.udp); + + log_line("Received a packet via raw socket."); + return len - sizeof packet.ip - sizeof packet.udp; +} + /* Compute Internet Checksum for @count bytes beginning at location @addr. */ uint16_t checksum(void *addr, int count) { diff --git a/ndhc/packet.h b/ndhc/packet.h index 149fc77..9e7473b 100644 --- a/ndhc/packet.h +++ b/ndhc/packet.h @@ -1,5 +1,5 @@ /* packet.h - send and react to DHCP message packets - * Time-stamp: <2011-03-30 23:57:02 nk> + * Time-stamp: <2011-06-11 11:03:14 njk> * * (c) 2004-2011 Nicholas J. Kain * (c) 2001 Russ Dill @@ -66,7 +66,6 @@ enum { DHCP_SIZE = sizeof(struct dhcpMessage), }; -int get_packet(struct dhcpMessage *packet, int fd); uint16_t checksum(void *addr, int count); int raw_packet(struct dhcpMessage *payload, uint32_t source_ip, int source_port, uint32_t dest_ip, int dest_port,