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/* vi: set sw=4 ts=4: */
/*
* Mini nsenter implementation for busybox.
*
* Copyright (C) 2016 by Bartosz Golaszewski <bartekgola@gmail.com>
*
* Licensed under GPLv2 or later, see file LICENSE in this source tree.
*/
//config:config NSENTER
//config: bool "nsenter (8.6 kb)"
//config: default y
//config: select PLATFORM_LINUX
//config: help
//config: Run program with namespaces of other processes.
//applet:IF_NSENTER(APPLET(nsenter, BB_DIR_USR_BIN, BB_SUID_DROP))
//kbuild:lib-$(CONFIG_NSENTER) += nsenter.o
//usage:#define nsenter_trivial_usage
//usage: "[OPTIONS] [PROG [ARGS]]"
//usage:#define nsenter_full_usage "\n"
//usage: "\n -t PID Target process to get namespaces from"
//usage: "\n -m[FILE] Enter mount namespace"
//usage: "\n -u[FILE] Enter UTS namespace (hostname etc)"
//usage: "\n -i[FILE] Enter System V IPC namespace"
//usage: "\n -n[FILE] Enter network namespace"
//usage: "\n -p[FILE] Enter pid namespace"
//usage: "\n -U[FILE] Enter user namespace"
//usage: "\n -S UID Set uid in entered namespace"
//usage: "\n -G GID Set gid in entered namespace"
//usage: IF_LONG_OPTS(
//usage: "\n --preserve-credentials Don't touch uids or gids"
//usage: )
//usage: "\n -r[DIR] Set root directory"
//usage: "\n -w[DIR] Set working directory"
//usage: "\n -F Don't fork before exec'ing PROG"
#include <sched.h>
#ifndef CLONE_NEWUTS
# define CLONE_NEWUTS 0x04000000
#endif
#ifndef CLONE_NEWIPC
# define CLONE_NEWIPC 0x08000000
#endif
#ifndef CLONE_NEWUSER
# define CLONE_NEWUSER 0x10000000
#endif
#ifndef CLONE_NEWPID
# define CLONE_NEWPID 0x20000000
#endif
#ifndef CLONE_NEWNET
# define CLONE_NEWNET 0x40000000
#endif
#include "libbb.h"
struct namespace_descr {
int flag; /* value passed to setns() */
char ns_nsfile8[8]; /* "ns/" + namespace file in process' procfs entry */
};
struct namespace_ctx {
char *path; /* optional path to a custom ns file */
int fd; /* opened namespace file descriptor */
};
enum {
OPT_user = 1 << 0,
OPT_ipc = 1 << 1,
OPT_uts = 1 << 2,
OPT_network = 1 << 3,
OPT_pid = 1 << 4,
OPT_mount = 1 << 5,
OPT_target = 1 << 6,
OPT_setuid = 1 << 7,
OPT_setgid = 1 << 8,
OPT_root = 1 << 9,
OPT_wd = 1 << 10,
OPT_nofork = 1 << 11,
OPT_prescred = (1 << 12) * ENABLE_LONG_OPTS,
};
enum {
NS_USR_POS = 0,
NS_IPC_POS,
NS_UTS_POS,
NS_NET_POS,
NS_PID_POS,
NS_MNT_POS,
NS_COUNT,
};
/*
* The order is significant in nsenter.
* The user namespace comes first, so that it is entered first.
* This gives an unprivileged user the potential to enter other namespaces.
*/
static const struct namespace_descr ns_list[] = {
{ CLONE_NEWUSER, "ns/user", },
{ CLONE_NEWIPC, "ns/ipc", },
{ CLONE_NEWUTS, "ns/uts", },
{ CLONE_NEWNET, "ns/net", },
{ CLONE_NEWPID, "ns/pid", },
{ CLONE_NEWNS, "ns/mnt", },
};
/*
* Upstream nsenter doesn't support the short option for --preserve-credentials
*/
static const char opt_str[] ALIGN1 = "U::i::u::n::p::m::""t+S+G+r::w::F";
#if ENABLE_LONG_OPTS
static const char nsenter_longopts[] ALIGN1 =
"user\0" Optional_argument "U"
"ipc\0" Optional_argument "i"
"uts\0" Optional_argument "u"
"network\0" Optional_argument "n"
"pid\0" Optional_argument "p"
"mount\0" Optional_argument "m"
"target\0" Required_argument "t"
"setuid\0" Required_argument "S"
"setgid\0" Required_argument "G"
"root\0" Optional_argument "r"
"wd\0" Optional_argument "w"
"no-fork\0" No_argument "F"
"preserve-credentials\0" No_argument "\xff"
;
#endif
/*
* Open a file and return the new descriptor. If a full path is provided in
* fs_path, then the file to which it points is opened. Otherwise (fd_path is
* NULL) the routine builds a path to a procfs file using the following
* template: '/proc/<target_pid>/<target_file>'.
*/
static int open_by_path_or_target(const char *path,
pid_t target_pid, const char *target_file)
{
char proc_path_buf[sizeof("/proc/%u/1234567890") + sizeof(int)*3];
if (!path) {
if (target_pid == 0) {
/* Example:
* "nsenter -p PROG" - neither -pFILE nor -tPID given.
*/
bb_show_usage();
}
snprintf(proc_path_buf, sizeof(proc_path_buf),
"/proc/%u/%s", (unsigned)target_pid, target_file);
path = proc_path_buf;
}
return xopen(path, O_RDONLY);
}
int nsenter_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int nsenter_main(int argc UNUSED_PARAM, char **argv)
{
int i;
unsigned int opts;
const char *root_dir_str = NULL;
const char *wd_str = NULL;
struct namespace_ctx ns_ctx_list[NS_COUNT];
int setgroups_failed;
int root_fd, wd_fd;
int target_pid = 0;
int uid = 0;
int gid = 0;
memset(ns_ctx_list, 0, sizeof(ns_ctx_list));
opts = getopt32long(argv, opt_str, nsenter_longopts,
&ns_ctx_list[NS_USR_POS].path,
&ns_ctx_list[NS_IPC_POS].path,
&ns_ctx_list[NS_UTS_POS].path,
&ns_ctx_list[NS_NET_POS].path,
&ns_ctx_list[NS_PID_POS].path,
&ns_ctx_list[NS_MNT_POS].path,
&target_pid, &uid, &gid,
&root_dir_str, &wd_str
);
argv += optind;
root_fd = wd_fd = -1;
if (opts & OPT_root)
root_fd = open_by_path_or_target(root_dir_str,
target_pid, "root");
if (opts & OPT_wd)
wd_fd = open_by_path_or_target(wd_str, target_pid, "cwd");
for (i = 0; i < NS_COUNT; i++) {
const struct namespace_descr *ns = &ns_list[i];
struct namespace_ctx *ns_ctx = &ns_ctx_list[i];
ns_ctx->fd = -1;
if (opts & (1 << i))
ns_ctx->fd = open_by_path_or_target(ns_ctx->path,
target_pid, ns->ns_nsfile8);
}
/*
* Entering the user namespace without --preserve-credentials implies
* --setuid & --setgid and clearing root's groups.
*/
setgroups_failed = 0;
if ((opts & OPT_user) && !(opts & OPT_prescred)) {
opts |= (OPT_setuid | OPT_setgid);
/*
* We call setgroups() before and after setns() and only
* bail-out if it fails twice.
*/
setgroups_failed = (setgroups(0, NULL) < 0);
}
for (i = 0; i < NS_COUNT; i++) {
const struct namespace_descr *ns = &ns_list[i];
struct namespace_ctx *ns_ctx = &ns_ctx_list[i];
if (ns_ctx->fd < 0)
continue;
if (setns(ns_ctx->fd, ns->flag)) {
bb_perror_msg_and_die(
"setns(): can't reassociate to namespace '%s'",
ns->ns_nsfile8 + 3 /* skip over "ns/" */
);
}
close(ns_ctx->fd); /* should close fds, to not confuse exec'ed PROG */
/*ns_ctx->fd = -1;*/
}
if (root_fd >= 0) {
if (wd_fd < 0) {
/*
* Save the current working directory if we're not
* changing it.
*/
wd_fd = xopen(".", O_RDONLY);
}
xfchdir(root_fd);
xchroot(".");
close(root_fd);
/*root_fd = -1;*/
}
if (wd_fd >= 0) {
xfchdir(wd_fd);
close(wd_fd);
/*wd_fd = -1;*/
}
/*
* Entering the pid namespace implies forking unless it's been
* explicitly requested by the user not to.
*/
if (!(opts & OPT_nofork) && (opts & OPT_pid)) {
xvfork_parent_waits_and_exits();
/* Child continues */
}
if (opts & OPT_setgid) {
if (setgroups(0, NULL) < 0 && setgroups_failed)
bb_perror_msg_and_die("setgroups");
xsetgid(gid);
}
if (opts & OPT_setuid)
xsetuid(uid);
exec_prog_or_SHELL(argv);
}
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