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merd: Switch to AF_UNIX for qemu tap, provide wrapper

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We can bypass a full-fledged network interface between qemu and merd by
connecting the qemu tap file descriptor to a provided UNIX domain
socket: this could be implemented in qemu eventually, qrap covers this
meanwhile.

This also avoids the need for the AF_PACKET socket towards the guest.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
Stefano Brivio 2020-07-18 01:02:39 +02:00
parent cefcf0bc2c
commit fa2d20908d
3 changed files with 149 additions and 68 deletions
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9
Makefile
View file

@ -1,10 +1,13 @@
CFLAGS += -Wall -Wextra -pedantic
all: merd
all: merd qrap
merd: merd.c
merd: merd.c merd.h
$(CC) $(CFLAGS) merd.c -o merd
qrap: qrap.c merd.h
$(CC) $(CFLAGS) qrap.o -o qrap
.PHONY: clean
clean:
-${RM} merd
-${RM} merd qrap

129
merd.c
View file

@ -1,13 +1,14 @@
/* MERD - MacVTap Egress and Routing Daemon
*
* merd.c - Daemon implementation
*
* Author: Stefano Brivio <sbrivio@redhat.com>
* License: GPLv2
*
* Grab packets from Ethernet interface via AF_PACKET, build AF_INET sockets for
* each 5-tuple from ICMP, TCP, UDP packets, perform connection tracking and
* forward them with destination address NAT. Forward packets received on
* sockets back to the AF_PACKET interface (typically, a macvtap, tap or veth
* interface towards a network namespace or a VM).
* Grab Ethernet frames via AF_UNIX socket, build AF_INET sockets for each
* 5-tuple from ICMP, TCP, UDP packets, perform connection tracking and forward
* them with destination address NAT. Forward packets received on sockets back
* to the UNIX domain socket (typically, a tap file descriptor from qemu).
*
* TODO:
* - steal packets from AF_INET sockets (using eBPF/XDP, or a new socket
@ -27,6 +28,7 @@
#include <sys/epoll.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/un.h>
#include <ifaddrs.h>
#include <linux/if_ether.h>
#include <linux/if_packet.h>
@ -44,6 +46,8 @@
#include <errno.h>
#include <linux/ip.h>
#include "merd.h"
#define EPOLL_EVENTS 10
#define CT_SIZE 4096
@ -73,54 +77,40 @@ struct ct4 {
* struct ctx - Execution context
* @epollfd: file descriptor for epoll instance
* @ext_addr4: IPv4 address for external, routable interface
* @tap_idx: Interface index for tap interface
* @fd_tap4: IPv4 AF_PACKET socket for tap interface
* @fd_unix: AF_UNIX socket for tap file descriptor
* @map4: Connection tracking table
*/
struct ctx {
int epollfd;
unsigned long ext_addr4;
int tap_idx;
int fd_tap4;
int fd_unix;
struct ct4 map4[CT_SIZE];
};
/**
* sock4_l3() - Create and bind AF_PACKET socket for IPv4, add to epoll list
* @c: Execution context
* @ifn: Name of tap interface
* @type: AF_PACKET protocol type
* sock_unix() - Create and bind AF_UNIX socket, add to epoll list
*
* Return: newly created socket, doesn't return on error
*/
static int sock4_l3(struct ctx *c, const char *ifn, int type)
static int sock_unix(void)
{
struct sockaddr_ll addr = {
.sll_family = AF_PACKET,
.sll_protocol = htons(ETH_P_IP),
.sll_ifindex = if_nametoindex(ifn),
struct sockaddr_un addr = {
.sun_family = AF_UNIX,
.sun_path = UNIX_SOCK_PATH,
};
struct epoll_event ev = { 0 };
int fd;
fd = socket(AF_PACKET, type, htons(ETH_P_IP));
fd = socket(AF_UNIX, SOCK_STREAM, 0);
if (fd < 0) {
perror("L3 socket");
perror("UNIX socket");
exit(EXIT_FAILURE);
}
unlink(UNIX_SOCK_PATH);
if (bind(fd, (const struct sockaddr *)&addr, sizeof(addr)) < 0) {
perror("L3 bind");
perror("UNIX socket bind");
exit(EXIT_FAILURE);
}
ev.events = EPOLLIN;
ev.data.fd = fd;
if (epoll_ctl(c->epollfd, EPOLL_CTL_ADD, fd, &ev) == -1) {
perror("epoll_ctl");
exit(EXIT_FAILURE);
}
return fd;
}
@ -207,7 +197,7 @@ static int sock4_l4(struct ctx *c, uint16_t proto, uint16_t port)
*/
void usage(const char *name)
{
fprintf(stderr, "Usage: %s IF_TAP IF_EXT\n", name);
fprintf(stderr, "Usage: %s IF_EXT\n", name);
exit(EXIT_FAILURE);
}
@ -411,7 +401,7 @@ static void csum_tcp4(uint16_t *in)
}
/**
* tap4_handler() - Packet handler for tap interface
* tap4_handler() - Packet handler for tap file descriptor
* @c: Execution context
* @len: Total L2 packet length
* @in: Packet buffer, L2 headers
@ -433,21 +423,6 @@ static void tap4_handler(struct ctx *c, int len, char *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)),
@ -463,6 +438,21 @@ static void tap4_handler(struct ctx *c, int len, char *in)
fd);
}
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 (sendto(fd, in + sizeof(struct ethhdr) + sizeof(struct iphdr),
len - sizeof(struct ethhdr) - 4 * iph->ihl, 0,
(struct sockaddr *)&addr, sizeof(addr)) < 0)
@ -478,12 +468,6 @@ static void tap4_handler(struct ctx *c, int len, char *in)
*/
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];
@ -507,8 +491,6 @@ static void ext4_handler(struct ctx *c, int len, char *in)
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);
@ -531,9 +513,8 @@ static void ext4_handler(struct ctx *c, int len, char *in)
ntohs(th->dest));
}
if (sendto(c->fd_tap4, buf, len + sizeof(struct ethhdr), 0,
(struct sockaddr *)&addr, sizeof(addr)) < 0)
perror("sendto");
if (send(c->fd_unix, buf, len + sizeof(struct ethhdr), 0) < 0)
perror("send");
}
/**
@ -546,18 +527,18 @@ static void ext4_handler(struct ctx *c, int len, char *in)
int main(int argc, char **argv)
{
struct epoll_event events[EPOLL_EVENTS];
const char *if_tap, *if_ext;
struct epoll_event ev = { 0 };
struct ctx c = { 0 };
const char *if_ext;
char buf[1 << 16];
int nfds, i, len;
int fd_unix;
if (argc != 3)
if (argc != 2)
usage(argv[0]);
if_tap = argv[1];
if_ext = argv[2];
if_ext = argv[1];
getaddrs_ext(&c, if_ext);
c.tap_idx = if_nametoindex(if_tap);
c.epollfd = epoll_create1(0);
if (c.epollfd == -1) {
@ -565,7 +546,17 @@ int main(int argc, char **argv)
exit(EXIT_FAILURE);
}
c.fd_tap4 = sock4_l3(&c, if_tap, SOCK_RAW);
fd_unix = sock_unix();
listen:
listen(fd_unix, 1);
fprintf(stderr,
"You can now start qrap:\n\t"
"./qrap 42 kvm ... -net tap,fd=42 -net nic,model=virtio ...\n");
c.fd_unix = accept(fd_unix, NULL, NULL);
ev.events = EPOLLIN;
ev.data.fd = c.fd_unix;
epoll_ctl(c.epollfd, EPOLL_CTL_ADD, c.fd_unix, &ev);
loop:
nfds = epoll_wait(c.epollfd, events, EPOLL_EVENTS, -1);
@ -576,15 +567,23 @@ loop:
for (i = 0; i < nfds; i++) {
len = recv(events[i].data.fd, buf, sizeof(buf), MSG_DONTWAIT);
if (events[i].data.fd == c.fd_unix && len <= 0) {
epoll_ctl(c.epollfd, EPOLL_CTL_DEL, c.fd_unix, &ev);
close(c.fd_unix);
goto listen;
}
if (len == 0)
continue;
if (len < 0) {
if (errno == EAGAIN || errno == EWOULDBLOCK)
break;
goto out;
}
if (events[i].data.fd == c.fd_tap4)
if (events[i].data.fd == c.fd_unix)
tap4_handler(&c, len, buf);
else
ext4_handler(&c, len, buf);

79
qrap.c Normal file
View file

@ -0,0 +1,79 @@
/* MERD - MacVTap Egress and Routing Daemon
*
* qrap.c - qemu wrapper connecting UNIX domain socket to tap file descriptor
*
* Author: Stefano Brivio <sbrivio@redhat.com>
* License: GPLv2
*
* TODO: Implement this functionality directly in qemu: we have TCP and UDP
* socket back-ends already.
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <errno.h>
#include <limits.h>
#include "merd.h"
/**
* usage() - Print usage and exit
* @name: Executable name
*/
void usage(const char *name)
{
fprintf(stderr, "Usage: %s FDNUM QEMU_CMD ...\n", name);
exit(EXIT_FAILURE);
}
/**
* main() - Entry point and main loop
* @argc: Argument count
* @argv: File descriptor number, then qemu with arguments
*
* Return: 0 once interrupted, non-zero on failure
*/
int main(int argc, char **argv)
{
struct sockaddr_un addr = {
.sun_family = AF_UNIX,
.sun_path = UNIX_SOCK_PATH,
};
long fd;
int s;
if (argc < 3)
usage(argv[0]);
fd = strtol(argv[1], NULL, 0);
if (fd < 3 || fd > INT_MAX || errno)
usage(argv[0]);
s = socket(AF_UNIX, SOCK_STREAM, 0);
if (s < 0) {
perror("socket");
exit(EXIT_FAILURE);
}
if (connect(s, (const struct sockaddr *)&addr, sizeof(addr)) < 0) {
perror("connect");
exit(EXIT_FAILURE);
}
if (dup2(s, (int)fd) < 0) {
perror("dup");
exit(EXIT_FAILURE);
}
close(s);
execvp(argv[2], argv + 2);
perror("execvp");
return EXIT_FAILURE;
}