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merd: Initial import
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
Stefano Brivio
commit
cefcf0bc2c
10
Makefile
Normal file
10
Makefile
Normal file
@ -0,0 +1,10 @@
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CFLAGS += -Wall -Wextra -pedantic
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all: merd
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merd: merd.c
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$(CC) $(CFLAGS) merd.c -o merd
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.PHONY: clean
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clean:
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-${RM} merd
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597
merd.c
Normal file
597
merd.c
Normal file
@ -0,0 +1,597 @@
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/* MERD - MacVTap Egress and Routing Daemon
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*
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* Author: Stefano Brivio <sbrivio@redhat.com>
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* License: GPLv2
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*
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* Grab packets from Ethernet interface via AF_PACKET, build AF_INET sockets for
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* each 5-tuple from ICMP, TCP, UDP packets, perform connection tracking and
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* forward them with destination address NAT. Forward packets received on
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* sockets back to the AF_PACKET interface (typically, a macvtap, tap or veth
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* interface towards a network namespace or a VM).
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*
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* TODO:
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* - steal packets from AF_INET sockets (using eBPF/XDP, or a new socket
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* option): currently, incoming packets are also handled by in-kernel protocol
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* handlers, so every incoming untracked TCP packet gets a RST. Workaround:
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* iptables -A OUTPUT -m state --state INVALID,NEW,ESTABLISHED \
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* -p tcp --tcp-flags RST RST -j DROP
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* - and use XDP sockmap on top of that to improve performance
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* - add IPv6 support. Current workaround on the namespace or machine on the
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* tap side:
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* echo 1 > /proc/sys/net/ipv6/conf/all/disable_ipv6
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* - reserve and translate ports
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* - aging and timeout/RST bookkeeping for connection tracking entries
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*/
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#include <stdio.h>
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#include <sys/epoll.h>
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#include <sys/socket.h>
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#include <sys/types.h>
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#include <ifaddrs.h>
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#include <linux/if_ether.h>
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#include <linux/if_packet.h>
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#include <linux/ipv6.h>
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#include <linux/tcp.h>
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#include <linux/udp.h>
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#include <linux/if_link.h>
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#include <net/ethernet.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <arpa/inet.h>
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#include <net/if.h>
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#include <netdb.h>
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#include <string.h>
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#include <errno.h>
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#include <linux/ip.h>
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#define EPOLL_EVENTS 10
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#define CT_SIZE 4096
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/**
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* struct ct4 - IPv4 connection tracking entry
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* @p: IANA protocol number
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* @sa: Source address (as seen from tap interface)
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* @da: Destination address
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* @sp: Source port, network order
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* @dp: Destination port, network order
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* @hd: Destination MAC address
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* @hs: Source MAC address
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* @fd: File descriptor for corresponding AF_INET socket
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*/
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struct ct4 {
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uint8_t p;
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uint32_t sa;
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uint32_t da;
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uint16_t sp;
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uint16_t dp;
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unsigned char hd[ETH_ALEN];
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unsigned char hs[ETH_ALEN];
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int fd;
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};
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/**
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* struct ctx - Execution context
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* @epollfd: file descriptor for epoll instance
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* @ext_addr4: IPv4 address for external, routable interface
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* @tap_idx: Interface index for tap interface
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* @fd_tap4: IPv4 AF_PACKET socket for tap interface
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* @map4: Connection tracking table
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*/
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struct ctx {
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int epollfd;
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unsigned long ext_addr4;
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int tap_idx;
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int fd_tap4;
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struct ct4 map4[CT_SIZE];
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};
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/**
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* sock4_l3() - Create and bind AF_PACKET socket for IPv4, add to epoll list
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* @c: Execution context
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* @ifn: Name of tap interface
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* @type: AF_PACKET protocol type
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*
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* Return: newly created socket, doesn't return on error
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*/
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static int sock4_l3(struct ctx *c, const char *ifn, int type)
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{
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struct sockaddr_ll addr = {
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.sll_family = AF_PACKET,
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.sll_protocol = htons(ETH_P_IP),
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.sll_ifindex = if_nametoindex(ifn),
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};
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struct epoll_event ev = { 0 };
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int fd;
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fd = socket(AF_PACKET, type, htons(ETH_P_IP));
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if (fd < 0) {
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perror("L3 socket");
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exit(EXIT_FAILURE);
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}
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if (bind(fd, (const struct sockaddr *)&addr, sizeof(addr)) < 0) {
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perror("L3 bind");
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exit(EXIT_FAILURE);
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}
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ev.events = EPOLLIN;
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ev.data.fd = fd;
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if (epoll_ctl(c->epollfd, EPOLL_CTL_ADD, fd, &ev) == -1) {
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perror("epoll_ctl");
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exit(EXIT_FAILURE);
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}
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return fd;
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}
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/**
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* getaddrs_ext() - Fetch IP addresses of external routable interface
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* @c: Execution context
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* @ifn: Name of external interface
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*/
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static void getaddrs_ext(struct ctx *c, const char *ifn)
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{
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struct ifaddrs *ifaddr, *ifa;
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if (getifaddrs(&ifaddr) == -1) {
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perror("getifaddrs");
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exit(EXIT_FAILURE);
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}
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for (ifa = ifaddr; ifa; ifa = ifa->ifa_next) {
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struct sockaddr_in *in_addr;
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if (strcmp(ifa->ifa_name, ifn))
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continue;
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if (!ifa->ifa_addr)
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continue;
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if (ifa->ifa_addr->sa_family != AF_INET)
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continue;
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in_addr = (struct sockaddr_in *)ifa->ifa_addr;
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c->ext_addr4 = in_addr->sin_addr.s_addr;
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freeifaddrs(ifaddr);
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return;
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}
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fprintf(stderr, "Couldn't get IPv4 address for external interface\n");
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freeifaddrs(ifaddr);
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exit(EXIT_FAILURE);
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}
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/**
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* sock4_l4() - Create and bind AF_INET socket for given L4, add to epoll list
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* @c: Execution context
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* @proto: Protocol number, network order
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* @port: L4 port, network order
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*
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* Return: newly created socket, -1 on error
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*/
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static int sock4_l4(struct ctx *c, uint16_t proto, uint16_t port)
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{
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struct sockaddr_in addr = {
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.sin_family = AF_INET,
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.sin_port = port,
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.sin_addr = { .s_addr = c->ext_addr4 },
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};
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struct epoll_event ev = { 0 };
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int fd;
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fd = socket(AF_INET, SOCK_RAW, proto);
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if (fd < 0) {
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perror("L4 socket");
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return -1;
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}
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if (bind(fd, (const struct sockaddr *)&addr, sizeof(addr)) < 0) {
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perror("bind");
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close(fd);
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return -1;
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}
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ev.events = EPOLLIN;
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ev.data.fd = fd;
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if (epoll_ctl(c->epollfd, EPOLL_CTL_ADD, fd, &ev) == -1) {
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perror("epoll_ctl");
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return -1;
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}
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return fd;
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}
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/**
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* usage() - Print usage and exit
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* @name: Executable name
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*/
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void usage(const char *name)
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{
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fprintf(stderr, "Usage: %s IF_TAP IF_EXT\n", name);
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exit(EXIT_FAILURE);
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}
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/**
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* lookup4() - Look up socket entry from tap-sourced packet, create if missing
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* @c: Execution context
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* @in: Packet buffer, L2 headers
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*
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* Return: -1 for unsupported or too many sockets, matching socket otherwise
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*/
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static int lookup4(struct ctx *c, const char *in)
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{
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char buf_s[BUFSIZ], buf_d[BUFSIZ];
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struct ct4 *ct = c->map4;
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struct tcphdr *th;
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struct iphdr *iph;
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struct ethhdr *eh;
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int i;
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eh = (struct ethhdr *)in;
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iph = (struct iphdr *)(in + ETH_HLEN);
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th = (struct tcphdr *)(iph + 1);
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switch (iph->protocol) {
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case IPPROTO_ICMP:
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case IPPROTO_TCP:
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case IPPROTO_UDP:
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break;
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default:
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return -1;
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}
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for (i = 0; i < CT_SIZE; i++) {
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if (ct[i].p == iph->protocol &&
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ct[i].sa == iph->saddr && ct[i].da == iph->daddr &&
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(ct[i].p == IPPROTO_ICMP ||
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(ct[i].sp == th->source && ct[i].dp == th->dest)) &&
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!memcmp(ct[i].hd, eh->h_dest, ETH_ALEN) &&
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!memcmp(ct[i].hs, eh->h_source, ETH_ALEN))
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return ct[i].fd;
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}
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for (i = 0; i < CT_SIZE && ct[i].p; i++);
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if (i == CT_SIZE) {
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fprintf(stderr, "\nToo many sockets, aborting ");
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} else {
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ct[i].fd = sock4_l4(c, iph->protocol, th->source);
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fprintf(stderr, "\n(socket %i) New ", ct[i].fd);
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ct[i].p = iph->protocol;
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ct[i].sa = iph->saddr;
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ct[i].da = iph->daddr;
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if (iph->protocol != IPPROTO_ICMP) {
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ct[i].sp = th->source;
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ct[i].dp = th->dest;
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}
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memcpy(&ct[i].hd, eh->h_dest, ETH_ALEN);
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memcpy(&ct[i].hs, eh->h_source, ETH_ALEN);
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}
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if (iph->protocol == IPPROTO_ICMP) {
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fprintf(stderr, "icmp connection\n\tfrom %s to %s\n\n",
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inet_ntop(AF_INET, &iph->saddr, buf_s, sizeof(buf_s)),
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inet_ntop(AF_INET, &iph->daddr, buf_d, sizeof(buf_d)));
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} else {
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fprintf(stderr, "%s connection\n\tfrom %s:%i to %s:%i\n\n",
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getprotobynumber(iph->protocol)->p_name,
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inet_ntop(AF_INET, &iph->saddr, buf_s, sizeof(buf_s)),
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ntohs(th->source),
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inet_ntop(AF_INET, &iph->daddr, buf_d, sizeof(buf_d)),
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ntohs(th->dest));
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}
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return (i == CT_SIZE) ? -1 : ct[i].fd;
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}
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/**
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* lookup4_r4() - Reverse look up connection tracking entry from incoming packet
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* @ct: Connection tracking table
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* @in: Packet buffer, L3 headers
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*
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* Return: matching entry if any, NULL otherwise
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*/
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struct ct4 *lookup_r4(struct ct4 *ct, const char *in)
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{
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struct tcphdr *th;
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struct iphdr *iph;
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int i;
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iph = (struct iphdr *)in;
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th = (struct tcphdr *)(iph + 1);
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for (i = 0; i < CT_SIZE; i++) {
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if (iph->protocol == ct[i].p &&
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iph->saddr == ct[i].da &&
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(iph->protocol == IPPROTO_ICMP ||
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(th->source == ct[i].dp && th->dest == ct[i].sp)))
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return &ct[i];
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}
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return NULL;
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}
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/**
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* nat4_out() - Perform outgoing IPv4 address translation
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* @addr: Source address to be used
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* @in: Packet buffer, L3 headers
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*/
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static void nat4_out(unsigned long addr, const char *in)
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{
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struct iphdr *iph = (struct iphdr *)in;
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iph->saddr = addr;
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}
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/**
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* nat4_in() - Perform incoming IPv4 address translation
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* @addr: Original destination address to be used
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* @in: Packet buffer, L3 headers
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*/
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static void nat_in(unsigned long addr, const char *in)
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{
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struct iphdr *iph = (struct iphdr *)in;
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iph->daddr = addr;
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}
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/**
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* csum_fold() - Fold long sum for IP and TCP checksum
|
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* @sum: Original long sum
|
||||
*
|
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* Return: 16-bit folded sum
|
||||
*/
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||||
static uint16_t csum_fold(uint32_t sum)
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||||
{
|
||||
while (sum >> 16)
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sum = (sum & 0xffff) + (sum >> 16);
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|
||||
return sum;
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||||
}
|
||||
|
||||
/**
|
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* csum_ipv4() - Calculate IPv4 checksum
|
||||
* @buf: Packet buffer, L3 headers
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||||
* @len: Total L3 packet length
|
||||
*
|
||||
* Return: 16-bit IPv4-style checksum
|
||||
*/
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||||
static uint16_t csum_ip4(void *buf, size_t len)
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{
|
||||
uint32_t sum = 0;
|
||||
uint16_t *p = buf;
|
||||
size_t len1 = len / 2;
|
||||
size_t off;
|
||||
|
||||
for (off = 0; off < len1; off++, p++)
|
||||
sum += *p;
|
||||
|
||||
if (len % 2)
|
||||
sum += *p & 0xff;
|
||||
|
||||
return ~csum_fold(sum);
|
||||
}
|
||||
|
||||
/**
|
||||
* csum_ipv4() - Calculate TCP checksum for IPv4 and set in place
|
||||
* @in: Packet buffer, L3 headers
|
||||
*/
|
||||
static void csum_tcp4(uint16_t *in)
|
||||
{
|
||||
struct iphdr *iph = (struct iphdr *)in;
|
||||
struct tcphdr *th;
|
||||
uint16_t tcp_len;
|
||||
uint32_t sum = 0;
|
||||
|
||||
tcp_len = ntohs(iph->tot_len) - (iph->ihl << 2);
|
||||
th = (struct tcphdr *)(iph + 1);
|
||||
in = (uint16_t *)th;
|
||||
|
||||
sum += (iph->saddr >> 16) & 0xffff;
|
||||
sum += iph->saddr & 0xffff;
|
||||
sum += (iph->daddr >> 16) & 0xffff;
|
||||
sum += iph->daddr & 0xffff;
|
||||
|
||||
sum += htons(IPPROTO_TCP);
|
||||
sum += htons(tcp_len);
|
||||
|
||||
th->check = 0;
|
||||
while (tcp_len > 1) {
|
||||
sum += *in++;
|
||||
tcp_len -= 2;
|
||||
}
|
||||
|
||||
if (tcp_len > 0) {
|
||||
sum += *in & htons(0xff00);
|
||||
}
|
||||
|
||||
th->check = (uint16_t)~csum_fold(sum);
|
||||
}
|
||||
|
||||
/**
|
||||
* tap4_handler() - Packet handler for tap interface
|
||||
* @c: Execution context
|
||||
* @len: Total L2 packet length
|
||||
* @in: Packet buffer, L2 headers
|
||||
*/
|
||||
static void tap4_handler(struct ctx *c, int len, char *in)
|
||||
{
|
||||
struct iphdr *iph = (struct iphdr *)(in + ETH_HLEN);
|
||||
struct tcphdr *th = (struct tcphdr *)(iph + 1);
|
||||
struct udphdr *uh = (struct udphdr *)(iph + 1);
|
||||
struct sockaddr_in addr = {
|
||||
.sin_family = AF_INET,
|
||||
.sin_port = th->dest,
|
||||
.sin_addr = { .s_addr = iph->daddr },
|
||||
};
|
||||
char buf_s[BUFSIZ], buf_d[BUFSIZ];
|
||||
int fd;
|
||||
|
||||
fd = lookup4(c, in);
|
||||
if (fd == -1)
|
||||
return;
|
||||
|
||||
nat4_out(c->ext_addr4, in + ETH_HLEN);
|
||||
|
||||
switch (iph->protocol) {
|
||||
case IPPROTO_TCP:
|
||||
csum_tcp4((uint16_t *)(in + ETH_HLEN));
|
||||
break;
|
||||
case IPPROTO_UDP:
|
||||
uh->check = 0;
|
||||
break;
|
||||
case IPPROTO_ICMP:
|
||||
break;
|
||||
default:
|
||||
return;
|
||||
}
|
||||
|
||||
if (iph->protocol == IPPROTO_ICMP) {
|
||||
fprintf(stderr, "icmp from tap: %s -> %s (socket %i)\n",
|
||||
inet_ntop(AF_INET, &iph->saddr, buf_s, sizeof(buf_s)),
|
||||
inet_ntop(AF_INET, &iph->daddr, buf_d, sizeof(buf_d)),
|
||||
fd);
|
||||
} else {
|
||||
fprintf(stderr, "%s from tap: %s:%i -> %s:%i (socket %i)\n",
|
||||
getprotobynumber(iph->protocol)->p_name,
|
||||
inet_ntop(AF_INET, &iph->saddr, buf_s, sizeof(buf_s)),
|
||||
ntohs(th->source),
|
||||
inet_ntop(AF_INET, &iph->daddr, buf_d, sizeof(buf_d)),
|
||||
ntohs(th->dest),
|
||||
fd);
|
||||
}
|
||||
|
||||
if (sendto(fd, in + sizeof(struct ethhdr) + sizeof(struct iphdr),
|
||||
len - sizeof(struct ethhdr) - 4 * iph->ihl, 0,
|
||||
(struct sockaddr *)&addr, sizeof(addr)) < 0)
|
||||
perror("sendto");
|
||||
|
||||
}
|
||||
|
||||
/**
|
||||
* tap4_handler() - Packet handler for external routable interface
|
||||
* @c: Execution context
|
||||
* @len: Total L3 packet length
|
||||
* @in: Packet buffer, L3 headers
|
||||
*/
|
||||
static void ext4_handler(struct ctx *c, int len, char *in)
|
||||
{
|
||||
struct sockaddr_ll addr = {
|
||||
.sll_family = AF_PACKET,
|
||||
.sll_protocol = ntohs(ETH_P_IP),
|
||||
.sll_ifindex = c->tap_idx,
|
||||
.sll_halen = ETHER_ADDR_LEN,
|
||||
};
|
||||
struct iphdr *iph = (struct iphdr *)in;
|
||||
struct tcphdr *th = (struct tcphdr *)(iph + 1);
|
||||
char buf_s[BUFSIZ], buf_d[BUFSIZ];
|
||||
struct ethhdr *eh;
|
||||
struct ct4 *entry;
|
||||
char buf[1 << 16];
|
||||
|
||||
entry = lookup_r4(c->map4, in);
|
||||
if (!entry)
|
||||
return;
|
||||
|
||||
nat_in(entry->sa, in);
|
||||
|
||||
iph->check = 0;
|
||||
iph->check = csum_ip4(iph, 4 * iph->ihl);
|
||||
|
||||
if (iph->protocol == IPPROTO_TCP)
|
||||
csum_tcp4((uint16_t *)in);
|
||||
else if (iph->protocol == IPPROTO_UDP) {
|
||||
struct udphdr *uh = (struct udphdr *)(iph + 1);
|
||||
uh->check = 0;
|
||||
}
|
||||
|
||||
memcpy(&addr.sll_addr, entry->hs, ETH_ALEN);
|
||||
|
||||
eh = (struct ethhdr *)buf;
|
||||
memcpy(eh->h_dest, entry->hs, ETH_ALEN);
|
||||
memcpy(eh->h_source, entry->hd, ETH_ALEN);
|
||||
eh->h_proto = ntohs(ETH_P_IP);
|
||||
|
||||
memcpy(buf + sizeof(struct ethhdr), in, len);
|
||||
|
||||
if (iph->protocol == IPPROTO_ICMP) {
|
||||
fprintf(stderr, "icmp (socket %i) to tap: %s -> %s\n",
|
||||
entry->fd,
|
||||
inet_ntop(AF_INET, &iph->saddr, buf_s, sizeof(buf_s)),
|
||||
inet_ntop(AF_INET, &iph->daddr, buf_d, sizeof(buf_d)));
|
||||
} else {
|
||||
fprintf(stderr, "%s (socket %i) to tap: %s:%i -> %s:%i\n",
|
||||
getprotobynumber(iph->protocol)->p_name,
|
||||
entry->fd,
|
||||
inet_ntop(AF_INET, &iph->saddr, buf_s, sizeof(buf_s)),
|
||||
ntohs(th->source),
|
||||
inet_ntop(AF_INET, &iph->daddr, buf_d, sizeof(buf_d)),
|
||||
ntohs(th->dest));
|
||||
}
|
||||
|
||||
if (sendto(c->fd_tap4, buf, len + sizeof(struct ethhdr), 0,
|
||||
(struct sockaddr *)&addr, sizeof(addr)) < 0)
|
||||
perror("sendto");
|
||||
}
|
||||
|
||||
/**
|
||||
* main() - Entry point and main loop
|
||||
* @argc: Argument count
|
||||
* @argv: Interface names
|
||||
*
|
||||
* Return: 0 once interrupted, non-zero on failure
|
||||
*/
|
||||
int main(int argc, char **argv)
|
||||
{
|
||||
struct epoll_event events[EPOLL_EVENTS];
|
||||
const char *if_tap, *if_ext;
|
||||
struct ctx c = { 0 };
|
||||
char buf[1 << 16];
|
||||
int nfds, i, len;
|
||||
|
||||
if (argc != 3)
|
||||
usage(argv[0]);
|
||||
if_tap = argv[1];
|
||||
if_ext = argv[2];
|
||||
|
||||
getaddrs_ext(&c, if_ext);
|
||||
c.tap_idx = if_nametoindex(if_tap);
|
||||
|
||||
c.epollfd = epoll_create1(0);
|
||||
if (c.epollfd == -1) {
|
||||
perror("epoll_create1");
|
||||
exit(EXIT_FAILURE);
|
||||
}
|
||||
|
||||
c.fd_tap4 = sock4_l3(&c, if_tap, SOCK_RAW);
|
||||
|
||||
loop:
|
||||
nfds = epoll_wait(c.epollfd, events, EPOLL_EVENTS, -1);
|
||||
if (nfds == -1) {
|
||||
perror("epoll_wait");
|
||||
exit(EXIT_FAILURE);
|
||||
}
|
||||
|
||||
for (i = 0; i < nfds; i++) {
|
||||
len = recv(events[i].data.fd, buf, sizeof(buf), MSG_DONTWAIT);
|
||||
if (len == 0)
|
||||
continue;
|
||||
if (len < 0) {
|
||||
if (errno == EAGAIN || errno == EWOULDBLOCK)
|
||||
break;
|
||||
goto out;
|
||||
}
|
||||
|
||||
if (events[i].data.fd == c.fd_tap4)
|
||||
tap4_handler(&c, len, buf);
|
||||
else
|
||||
ext4_handler(&c, len, buf);
|
||||
}
|
||||
|
||||
goto loop;
|
||||
|
||||
out:
|
||||
return 0;
|
||||
}
|
||||
Loading…
Reference in New Issue
Block a user