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#define _GNU_SOURCE
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
#include <sched.h>
#include <getopt.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <limits.h>
#include <stdbool.h>
#include <sys/types.h>
#include <sys/wait.h>
#define myerror(f_, ...) { \
fprintf(stderr, (f_), ##__VA_ARGS__); \
rc = 1; \
goto end; \
}
#define stderror(prefix_) myerror(prefix_ ": %s.\n", strerror(errno)); \
static void usage(char* progname)
{
printf("Usage: %s OPTIONS COMMAND [ARGS...]\n\n", progname);
printf("Options:\n"
" -h, --help: show this help\n"
" -n, --nameserver NAMESERVER\n"
" -f, --ns-file FILE\n"
" -u, --uid UID\n"
" -g, --gid GID\n"
" -e, --env VAR=VALUE\n"
);
}
int main(int argc, char* argv[])
{
int rc = 0;
int temp_fd = 0;
int ns_fd = 0;
uid_t uid = 0;
uid_t gid = 0;
char cwd[PATH_MAX];
char temp_name[PATH_MAX] = {0};
char *ns_file = NULL;
char *nameserver = NULL;
bool ismounted;
int envi = 0;
size_t envn = sizeof(char*)*(argc/2);
char **envp = malloc(envn);
memset(envp, 0, envn);
if (argc < 2) {
usage(argv[0]);
return 1;
}
int opt;
struct option long_options[] = {
{"help", no_argument, NULL, 'h'},
{"nameserver", required_argument, NULL, 'n'},
{"ns-file", required_argument, NULL, 'f'},
{"uid", required_argument, NULL, 'u'},
{"gid", required_argument, NULL, 'g'},
{"env", required_argument, NULL, 'e'},
{0, 0, 0, 0}
};
while ((opt = getopt_long(argc, argv, "+hn:f:u:g:e:", long_options, NULL)) != EOF) {
switch (opt) {
case 'h':
usage(argv[0]);
return 0;
case 'n':
nameserver = optarg;
break;
case 'f':
ns_file = optarg;
break;
case 'u':
uid = (uid_t)atoi(optarg);
break;
case 'g':
gid = (uid_t)atoi(optarg);
break;
case 'e':
if (envi == envn-1)
fprintf(stderr, "warn: skipping --env %s\n", optarg);
else
envp[envi++] = optarg;
break;
default:
break;
}
}
if (nameserver == NULL)
myerror("error: --nameserver is required\n");
if (ns_file == NULL)
myerror("error: --ns-file is required\n");
if (geteuid() != 0)
myerror("error: you must be root.\n");
if (unshare(CLONE_NEWNS) == -1)
stderror("unshare");
/* save cwd */
getcwd(cwd, PATH_MAX);
/* create temp file */
strcpy(temp_name, "/tmp/capresolv.XXXXXX");
temp_fd = mkstemp(temp_name);
dprintf(temp_fd, "nameserver %s\n", nameserver);
close(temp_fd);
temp_fd = 0;
chmod(temp_name, 0644);
/* mount /etc/resolv.conf */
if (mount(temp_name, "/etc/resolv.conf", NULL, MS_BIND, NULL) == -1)
stderror("mount");
ismounted = true;
ns_fd = open(ns_file, O_RDONLY);
if (ns_fd == -1)
stderror("open");
/* change to netns */
if (setns(ns_fd, CLONE_NEWNET) == -1)
stderror("setns");
pid_t pid = fork();
if (!pid) {
/* change real and effective user and group (group first, then user) */
if (gid != getegid()) {
if (setregid(gid, gid) == -1)
stderror("setregid");
}
if (uid != geteuid()) {
if (setreuid(uid, uid) == -1)
myerror("setreuid");
}
/* restore cwd */
if (chdir(cwd) == -1)
stderror("chdir");
/* launch program */
if (execvpe(argv[optind], (char *const *)argv+optind, envp) == -1)
stderror("execvpe");
return 0;
}
waitpid(pid, NULL, 0);
end:
if (ismounted)
umount(temp_name);
if (temp_fd > 0)
close(temp_fd);
if (ns_fd > 0)
close(ns_fd);
if (temp_name[0] != 0)
unlink(temp_name);
return rc;
}
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