Use raw sockets for server

No more buffering, but auto-reply needs to be turned
off; see run_server.sh.

5 files changed, 66 insertions, 50 deletions

diff --git a/Makefile b/Makefile
index 84683dd..b1de31f 100644
--- a/Makefile
+++ b/Makefile
@@ -15,7 +15,7 @@ clean:
 
 
 server: server.o $(OBJECTS)
-	$(CC) $(CFLAGS) $^ -o $@ -lnetfilter_log
+	$(CC) $(CFLAGS) $^ -o $@
 
 client: client.o $(OBJECTS)
 	$(CC) $(CFLAGS) $^ -o $@
diff --git a/client.c b/client.c
index 527375f..1f8663f 100644
--- a/client.c
+++ b/client.c
@@ -25,6 +25,6 @@ int main(void) {
 		return 1;
 	}
 
-	printf("Received length: %zd\nPayload:\n", reply.length);
+	printf("Received length: %zd   payload:\n", reply.length);
 	xxd(reply.data, reply.length);
 }
diff --git a/icmp.c b/icmp.c
index e64580c..63436ac 100644
--- a/icmp.c
+++ b/icmp.c
@@ -2,6 +2,7 @@
 #include <stddef.h>
 #include <string.h>
 #include <assert.h>
+#include <unistd.h>
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <netinet/ip_icmp.h>
@@ -99,10 +100,6 @@ struct icmp_reply icmp_communicate(int sock, const char *ip_address, int seqnum,
 int icmp_send_echo_reply(const char *ip_address, int id, int seqnum, const void *data_, size_t length) {
 	const uint8_t *data = (const uint8_t*)data_;
 
-	int sock = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
-	int zero = 0;
-	assert(setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &zero, sizeof zero) >= 0);
-
 	struct sockaddr_in addr;
 	make_sockaddr(&addr, ip_address);
 
@@ -120,9 +117,14 @@ int icmp_send_echo_reply(const char *ip_address, int id, int seqnum, const void
 
 	msg.checksum = ~compute_checksum(&msg, total_length);
 
-	if (sendto(sock, &msg, ICMP_PAYLOAD_OFFSET + length, 0, (struct sockaddr*)&addr, sizeof addr) < 0) {
-		return -1;
-	}
+	int sock = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
+	// The below is only necessary for sending on IPPROTO_RAW sockets
+	// int zero = 0;
+	// assert(setsockopt(sock, IPPROTO_IP, IP_HDRINCL, &zero, sizeof zero) >= 0);
+
+	int ret = sendto(sock, &msg, ICMP_PAYLOAD_OFFSET + length, 0, (struct sockaddr*)&addr, sizeof addr);
+	close(sock);
+	if (ret < 0) return -1;
 
 	return 0;
 }
diff --git a/run_server.sh b/run_server.sh
new file mode 100755
index 0000000..50764b1
--- /dev/null
+++ b/run_server.sh
@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+sudo -v
+echo 1 | sudo tee /proc/sys/net/ipv4/icmp_echo_ignore_all
+sudo ./server
+echo 0 | sudo tee /proc/sys/net/ipv4/icmp_echo_ignore_all
diff --git a/server.c b/server.c
index 544c59b..db269e5 100644
--- a/server.c
+++ b/server.c
@@ -2,16 +2,12 @@
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdlib.h>
+#include <string.h>
 #include <unistd.h>
 #include <stdint.h>
 #include <arpa/inet.h>
 #include <netinet/ip.h>
-
-typedef uint8_t u_int8_t;
-typedef uint16_t u_int16_t;
-typedef uint32_t u_int32_t;
-#include <libnetfilter_log/libnetfilter_log.h>
-
+#include <netinet/ip_icmp.h>
 #include "icmp.h"
 #include "util.h"
 
@@ -20,7 +16,8 @@ struct state {
 	int socket;
 };
 
-static int icmp_callback(struct nflog_g_handle *gh, struct nfgenmsg *nfmsg, struct nflog_data *ldata, void *state_) {
+#if 0
+static int icmp_callback(struct nflog_data *ldata, void *state_) {
 	(void)gh; (void)nfmsg;
 
 	struct state *state = (struct state*)state_;
@@ -47,53 +44,65 @@ static int icmp_callback(struct nflog_g_handle *gh, struct nfgenmsg *nfmsg, stru
 
 	return 0;
 }
+#endif
 
 
 int main(void) {
-	struct nflog_handle *h = nflog_open();
-	if (!h) {
-		perror("nflog_open");
-		return 1;
-	}
-	if (nflog_unbind_pf(h, AF_INET) < 0) {
-		perror("nflog_unbind_pf");
-		return 1;
-	}
-	if (nflog_bind_pf(h, AF_INET) < 0) {
-		perror("nflog_bind_pf");
-		return 1;
-	}
-
-	struct nflog_g_handle *qh = nflog_bind_group(h, 0);
-	if (!qh) {
-		fprintf(stderr, "nflog_bind_group: no handle for group 0\n");
-		return 1;
-	}
-
-	if (nflog_set_mode(qh, NFULNL_COPY_PACKET, 0xffff) < 0) {
-		fprintf(stderr, "nflog_set_mode: can't set packet copy mode\n");
-		return 1;
-	}
-
-	struct state state;
+	// struct state state;
 	// state.socket = icmp_open_socket();
 	// if (state.socket < 0) {
 	//     perror("icmp_open_socket");
 	//     return 1;
 	// }
 
-	nflog_callback_register(qh, &icmp_callback, &state);
+	int sock = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
 
-	int fd = nflog_fd(h);
+	struct icmp_echo msg;
 
-	char buf[4096];
+	char buf[MAX_IP_PACKET_SIZE];
 	while (true) {
-		ssize_t nr = recv(fd, buf, sizeof buf, 0);
+		struct iovec iov1;
+		memset(&iov1, 0, sizeof iov1);
+		iov1.iov_base = buf;
+		iov1.iov_len = sizeof buf;
+
+		struct sockaddr_in addr;
+
+		struct msghdr recv_msghdr;
+		memset(&recv_msghdr, 0, sizeof recv_msghdr);
+		recv_msghdr.msg_name = &addr;
+		recv_msghdr.msg_namelen = sizeof addr;
+		recv_msghdr.msg_iov = &iov1;
+		recv_msghdr.msg_iovlen = 1;
+
+		ssize_t nr = recvmsg(sock, &recv_msghdr, 0);
 		if (nr < 0) break;
 
-		nflog_handle_packet(h, buf, nr);
-	}
+		// buf now contains received data starting at the IP header
+
+		printf("Full packet received:\n");
+		xxd(buf, nr);
 
-	nflog_unbind_group(qh);
-	nflog_close(h);
+		struct iphdr *hdr = (struct iphdr*)buf;
+		int hdr_len = hdr->ihl * 4;
+		uint32_t saddr = hdr->saddr;
+
+		struct icmp_echo *msg = (struct icmp_echo*)(buf + hdr_len);
+		int msg_len = nr - hdr_len;
+		printf("Received: type %u   code %u   id %hu   seqnum %hu   payload:\n",
+				(unsigned)msg->type, (unsigned)msg->code, msg->id, msg->seqnum);
+		xxd(msg->payload, msg_len - offsetof(struct icmp_echo, payload));
+
+		if (msg->type != ICMP_ECHO) {
+			printf("Not an ICMP_ECHO, ignoring\n");
+			continue;
+		}
+
+		uint8_t *saddr_bytes = (uint8_t*)&saddr;
+		char ip_address[16];
+		sprintf(ip_address, "%u.%u.%u.%u", saddr_bytes[0], saddr_bytes[1], saddr_bytes[2], saddr_bytes[3]);
+		if (icmp_send_echo_reply(ip_address, msg->id, msg->seqnum, "dank je wel", 11) < 0) {
+			perror("icmp_send_echo_reply");
+		}
+	}
 }