Move get_raw_packet() to packet.c and make get_packet() and get_raw_packet()

static functions.

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 <njkain at gmail dot com>
  * (c) 2001 Russ Dill <Russ.Dill@asu.edu>
@@ -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

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 <njkain at gmail dot com>
  * (c) 2001 Russ Dill <Russ.Dill@asu.edu>
@@ -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 */
+// Read a packet from a cooked socket.  Returns -1 on fatal error, -2 on
-int get_packet(struct dhcpMessage *packet, int fd)
+// 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)
 {

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 <njkain at gmail dot com>
  * (c) 2001 Russ Dill <Russ.Dill@asu.edu>
@@ -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,