274 lines
7.2 KiB
C
274 lines
7.2 KiB
C
/*-
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* Copyright (c) 2014 Juan Romero Pardines.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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/*
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* This is based on linux-user-chroot by Colin Walters, but has been adapted
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* specifically for xbps-src use:
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*
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* - This bind mounts exactly what we need, no support for additional mounts.
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* - This uses IPC/PID/mount namespaces, nothing more.
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* - Disables namespace features if running in OpenVZ containers.
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*/
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#define _GNU_SOURCE
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#include <sys/types.h>
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#include <sys/prctl.h>
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#include <sys/fsuid.h>
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#include <sys/mount.h>
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#include <sys/syscall.h>
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#include <sys/wait.h>
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#include <unistd.h>
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#include <stdio.h>
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#include <fcntl.h>
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#include <errno.h>
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#include <stdarg.h>
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#include <string.h>
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#include <assert.h>
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#include <stdlib.h>
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#include <sched.h>
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#include <limits.h> /* PATH_MAX */
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#ifndef SECBIT_NOROOT
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#define SECBIT_NOROOT (1 << 0)
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#endif
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#ifndef SECBIT_NOROOT_LOCKED
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#define SECBIT_NOROOT_LOCKED (1 << 1)
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#endif
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#ifndef PR_SET_NO_NEW_PRIVS
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#define PR_SET_NO_NEW_PRIVS 38
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#endif
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static void
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die(const char *fmt, ...)
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{
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va_list ap;
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int save_errno = errno;
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va_start(ap, fmt);
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fprintf(stderr, "ERROR ");
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vfprintf(stderr, fmt, ap);
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fprintf(stderr, " (%s)\n", strerror(save_errno));
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va_end(ap);
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exit(EXIT_FAILURE);
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}
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static void
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usage(const char *p)
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{
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printf("Usage: %s [-D dir] [-H dir] [-S dir] <chrootdir> <command>\n\n"
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"-D <distdir> Directory to be bind mounted at <chrootdir>/xbps-packages\n"
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"-H <hostdir> Directory to be bind mounted at <chrootdir>/host\n"
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"-S <shmdir> Directory to be bind mounted at <chrootdir>/<shmdir>\n", p);
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exit(EXIT_FAILURE);
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}
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static int
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fsuid_chdir(uid_t uid, const char *path)
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{
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int saveerrno, rv;
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(void)setfsuid(uid);
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rv = chdir(path);
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saveerrno = errno;
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(void)setfsuid(0);
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errno = saveerrno;
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return rv;
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}
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static int
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openvz_container(void)
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{
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if ((!access("/proc/vz/vzaquota", R_OK)) &&
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(!access("/proc/user_beancounters", R_OK)))
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return 1;
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return 0;
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}
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static void
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bindmount(uid_t ruid, const char *chrootdir, const char *dir, const char *dest)
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{
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char mountdir[PATH_MAX-1];
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snprintf(mountdir, sizeof(mountdir), "%s/%s", chrootdir, dest ? dest : dir);
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if (fsuid_chdir(ruid, dir) == -1)
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die("Couldn't chdir to %s", dir);
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if (mount(".", mountdir, NULL, MS_BIND|MS_PRIVATE, NULL) == -1)
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die("Failed to bind mount %s at %s", dir, mountdir);
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}
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int
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main(int argc, char **argv)
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{
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uid_t ruid, euid, suid;
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gid_t rgid, egid, sgid;
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const char *chrootdir, *distdir, *hostdir, *shmdir, *cmd, *argv0;
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char **cmdargs, mountdir[PATH_MAX-1];
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int aidx = 0, clone_flags, child_status = 0;
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pid_t child;
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chrootdir = distdir = hostdir = shmdir = cmd = NULL;
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argv0 = argv[0];
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argc--;
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argv++;
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if (argc < 2)
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usage(argv0);
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while (aidx < argc) {
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if (strcmp(argv[aidx], "-D") == 0) {
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/* distdir */
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distdir = argv[aidx+1];
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aidx += 2;
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} else if (strcmp(argv[aidx], "-H") == 0) {
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/* hostdir */
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hostdir = argv[aidx+1];
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aidx += 2;
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} else if (strcmp(argv[aidx], "-S") == 0) {
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/* shmdir */
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shmdir = argv[aidx+1];
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aidx += 2;
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} else {
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break;
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}
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}
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if ((argc - aidx) < 2)
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usage(argv0);
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chrootdir = argv[aidx];
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cmd = argv[aidx+1];
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cmdargs = argv + aidx + 1;
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/* Never allow chrootdir == / */
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if (strcmp(chrootdir, "/") == 0)
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die("/ is not allowed to be used as chrootdir");
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if (getresgid(&rgid, &egid, &sgid) == -1)
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die("getresgid");
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if (getresuid(&ruid, &euid, &suid) == -1)
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die("getresuid");
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if (rgid == 0)
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rgid = ruid;
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clone_flags = (SIGCHLD|CLONE_NEWNS|CLONE_NEWIPC|CLONE_NEWUTS|CLONE_NEWPID);
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if (openvz_container()) {
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/*
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* If running in a OpenVZ container simply disable all namespace
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* features.
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*/
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clone_flags &= ~(CLONE_NEWNS|CLONE_NEWIPC|CLONE_NEWUTS|CLONE_NEWPID);
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}
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/* Issue the clone(2) syscall with our settings */
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if ((child = syscall(__NR_clone, clone_flags, NULL)) == -1)
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die("clone");
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if (child == 0) {
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/*
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* Restrict privileges on the child.
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*/
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if (prctl(PR_SET_NO_NEW_PRIVS, 1) == -1 && errno != EINVAL) {
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die("prctl PR_SET_NO_NEW_PRIVS");
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} else if (prctl (PR_SET_SECUREBITS,
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SECBIT_NOROOT|SECBIT_NOROOT_LOCKED) == -1) {
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die("prctl SECBIT_NOROOT");
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}
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if (!openvz_container()) {
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/* Make / a private mount */
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if (mount(NULL, "/", "none", MS_PRIVATE|MS_REC, NULL) == -1)
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die("mount(/, MS_PRIVATE|MS_REC)");
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/* Remount / with nosuid just in case */
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if (mount (NULL, "/", "none", MS_PRIVATE|MS_REMOUNT|MS_NOSUID, NULL) == -1)
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die("mount(/, MS_PRIVATE|MS_REMOUNT|MS_NOSUID");
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}
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/* mount /proc */
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snprintf(mountdir, sizeof(mountdir), "%s/proc", chrootdir);
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if (mount("proc", mountdir, "proc", MS_MGC_VAL|MS_PRIVATE, NULL) == -1)
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die("Failed to mount %s", mountdir);
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/* bind mount /sys */
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bindmount(ruid, chrootdir, "/sys", NULL);
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/* bind mount /dev */
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bindmount(ruid, chrootdir, "/dev", NULL);
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/* bind mount hostdir if set */
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if (hostdir)
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bindmount(ruid, chrootdir, hostdir, "/host");
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/* bind mount distdir (if set) */
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if (distdir)
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bindmount(ruid, chrootdir, distdir, "/xbps-packages");
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/* bind mount shmdir (if set) */
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if (shmdir)
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bindmount(ruid, chrootdir, shmdir, NULL);
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/* move chrootdir to / and chroot to it */
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if (fsuid_chdir(ruid, chrootdir) == -1)
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die("Failed to chdir to %s", chrootdir);
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if (mount(".", ".", NULL, MS_BIND|MS_PRIVATE, NULL) == -1)
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die("Failed to bind mount %s", chrootdir);
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if (mount(chrootdir, "/", NULL, MS_MOVE, NULL) == -1)
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die("Failed to move %s as rootfs", chrootdir);
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if (chroot(".") == -1)
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die("Failed to chroot to %s", chrootdir);
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/* Switch back to the gid/uid of invoking process */
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if (setgid(rgid) == -1)
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die("setgid child");
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if (setuid(ruid) == -1)
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die("setuid child");
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if (execvp(cmd, cmdargs) == -1)
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die("Failed to execute command %s", cmd);
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}
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/* Switch back to the gid/uid of invoking process also in the parent */
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if (setgid(rgid) == -1)
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die("setgid child");
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if (setuid(ruid) == -1)
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die("setuid child");
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/* Wait until the child terminates */
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while (waitpid(child, &child_status, 0) < 0) {
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if (errno != EINTR)
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die("waitpid");
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}
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if (!WIFEXITED(child_status))
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return -1;
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return WEXITSTATUS(child_status);
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}
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