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#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sched.h>
#include <stdbool.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <linux/limits.h>
const char *var_name = "VOIDNSRUN_DIR";
const char *prog_version = "1.0";
#define USERMOUNTS_MAX 8
#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
#define ERROR(f_, ...) fprintf(stderr, (f_), ##__VA_ARGS__)
bool isdir(const char *s)
{
struct stat st;
int result = stat(s, &st);
if (result == -1)
ERROR("stat: %s\n", strerror(errno));
return result == 0 && S_ISDIR(st.st_mode);
}
void usage(const char *progname)
{
printf("Usage: %s [OPTIONS] PROGRAM [ARGS]\n", progname);
printf("\n"
"Options:\n"
" -m <path>: add bind mount\n"
" -r <path>: altroot path. If this option is not present,\n"
" %s environment variable is used.\n"
" -h: print this help\n"
" -v: print version\n",
var_name);
}
bool mountlist(
const char *dirptr,
size_t dirlen,
const char **mountpoints,
size_t len,
bool ignore_missing)
{
char buf[PATH_MAX];
for (size_t i = 0; i < len; i++) {
/* Check if it's safe to proceed. */
if (dirlen + strlen(mountpoints[i]) >= PATH_MAX) {
ERROR("error: path %s%s is too large.\n", dirptr, mountpoints[i]);
return false;
}
strcpy(buf, dirptr);
strcat(buf, mountpoints[i]);
if (!isdir(buf)) {
if (ignore_missing)
continue;
ERROR("error: source mount dir %s does not exists.\n", buf);
return false;
}
if (!isdir(mountpoints[i])) {
ERROR("error: mountpoint %s does not exists.\n", mountpoints[i]);
return false;
}
if (mount(buf, mountpoints[i], NULL, MS_BIND|MS_REC, NULL) == -1) {
ERROR("mount: failed to mount %s: %s\n",
mountpoints[i], strerror(errno));
return false;
}
}
return true;
}
int main(int argc, char **argv)
{
if (argc < 2) {
usage(argv[0]);
return 0;
}
int result;
char *dir = NULL;
size_t dirlen;
const char *usermounts[USERMOUNTS_MAX] = {0};
int usermounts_count = 0;
int c;
while ((c = getopt(argc, argv, "vhm:r:")) != -1) {
switch (c) {
case 'v':
printf("%s\n", prog_version);
return 0;
case 'h':
usage(argv[0]);
return 0;
case 'r':
dir = optarg;
break;
case 'm':
if (usermounts_count < USERMOUNTS_MAX) {
usermounts[usermounts_count++] = optarg;
break;
} else {
ERROR("error: only up to %d user mounts allowed.\n",
USERMOUNTS_MAX);
return 1;
}
case '?':
return 1;
}
}
/* Get alternative root dir. */
if (!dir)
dir = getenv(var_name);
if (!dir) {
ERROR("error: environment variable %s not found.\n", var_name);
return 1;
}
/* Validate it. */
if (!isdir(dir)) {
ERROR("error: %s is not a directory.\n", dir);
return 1;
}
dirlen = strlen(dir);
/* Do the unshare magic. */
result = unshare(CLONE_NEWNS);
if (result == -1) {
ERROR("unshare: %s\n", strerror(errno));
return 1;
}
/* Mount stuff from altroot to our private namespace. */
const char *mountpoints[] = {"/usr", "/var/db/xbps", "/etc/xbps.d"};
if (!mountlist(dir, dirlen, mountpoints, ARRAY_SIZE(mountpoints), true))
return 1;
if (usermounts_count > 0 &&
!mountlist(dir, dirlen, usermounts, usermounts_count, false))
return 1;
/* Drop root. */
uid_t uid = getuid();
gid_t gid = getgid();
result = setreuid(uid, uid);
if (result == -1) {
ERROR("setreuid: %s\n", strerror(errno));
return 1;
}
result = setregid(gid, gid);
if (result == -1) {
ERROR("setregid: %s\n", strerror(errno));
return 1;
}
/* Launch program. */
result = execvp(argv[optind], (char *const *)argv+optind);
if (result == -1) {
ERROR("execvp(%s): %s\n", argv[optind], strerror(errno));
return 1;
}
return 0;
}
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