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/*
* $Id: tundev.c 116 2005-10-30 14:18:08Z guillem $
*/
#define _GNU_SOURCE /* asprintf */
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <pwd.h>
#include <grp.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <net/if.h>
#include <linux/if_tun.h>
/* Tiny code to open tap/tun device, and hand the fd to qemu.
Run as root, drops to given user. */
int main(int argc, char *argv[])
{
struct ifreq ifr;
struct passwd *p;
unsigned int i;
char *newargs[argc + 1];
int fd;
if (argc < 4) {
fprintf(stderr,
"Usage: tundev user logfile qemu <qemu options>...\n");
exit(1);
}
fd = open("/dev/net/tun", O_RDWR);
if (fd < 0) {
perror("Could not open /dev/net/tun");
exit(1);
}
memset(&ifr, 0, sizeof(ifr));
ifr.ifr_flags = IFF_TAP | IFF_NO_PI;
strncpy(ifr.ifr_name, "tun%d", IFNAMSIZ);
if (ioctl(fd, TUNSETIFF, (void *) &ifr) != 0) {
perror("Could not get tun device");
exit(1);
}
/* Set userid. */
p = getpwnam(argv[1]);
if (!p) {
fprintf(stderr, "No user '%s'\n", argv[1]);
exit(1);
}
setgroups(0, NULL);
setgid(p->pw_gid);
if (setuid(p->pw_uid) != 0) {
perror("setting uid");
exit(1);
}
/* Insert -tun-fd */
newargs[0] = argv[3];
newargs[1] = "-tun-fd";
asprintf(&newargs[2], "%d", fd);
for (i = 4; i <= argc; i++)
newargs[i-1] = argv[i];
if (strcmp(argv[2], "-") == 0) {
execvp(newargs[0], newargs);
exit(1);
}
switch (fork()) {
case 0: {
close(1);
close(2);
open(argv[2], O_WRONLY|O_APPEND);
open(argv[2], O_WRONLY|O_APPEND);
close(0);
execvp(newargs[0], newargs);
exit(1);
}
case -1:
perror("fork failed");
exit(1);
}
printf("%s\n", ifr.ifr_name);
exit(0);
}
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