1 /* vi: set sw=4 ts=4: */
3 * Mini nsenter implementation for busybox.
5 * Copyright (C) 2016 by Bartosz Golaszewski <bartekgola@gmail.com>
7 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
10 //config:config NSENTER
11 //config: bool "nsenter"
13 //config: select PLATFORM_LINUX
15 //config: Run program with namespaces of other processes.
17 //config:config FEATURE_NSENTER_LONG_OPTS
18 //config: bool "Enable long options"
20 //config: depends on NSENTER && LONG_OPTS
22 //config: Support long options for the nsenter applet. This makes
23 //config: the busybox implementation more compatible with upstream.
25 //applet:IF_NSENTER(APPLET(nsenter, BB_DIR_USR_BIN, BB_SUID_DROP))
27 //kbuild:lib-$(CONFIG_NSENTER) += nsenter.o
29 //usage:#define nsenter_trivial_usage
30 //usage: "[OPTIONS] [PROG [ARGS]]"
31 //usage:#if ENABLE_FEATURE_NSENTER_LONG_OPTS
32 //usage:#define nsenter_full_usage "\n"
33 //usage: "\n -t, --target=PID Target process to get namespaces from"
34 //usage: "\n -m, --mount[=FILE] Enter mount namespace"
35 //usage: "\n -u, --uts[=FILE] Enter UTS namespace (hostname etc)"
36 //usage: "\n -i, --ipc[=FILE] Enter System V IPC namespace"
37 //usage: "\n -n, --net[=FILE] Enter network namespace"
38 //usage: "\n -p, --pid[=FILE] Enter pid namespace"
39 //usage: "\n -U, --user[=FILE] Enter user namespace"
40 //usage: "\n -S, --setuid=UID Set uid in entered namespace"
41 //usage: "\n -G, --setgid=GID Set gid in entered namespace"
42 //usage: "\n --preserve-credentials Don't touch uids or gids"
43 //usage: "\n -r, --root[=DIR] Set root directory"
44 //usage: "\n -w, --wd[=DIR] Set working directory"
45 //usage: "\n -F, --no-fork Don't fork before exec'ing PROG"
47 //usage:#define nsenter_full_usage "\n"
48 //usage: "\n -t PID Target process to get namespaces from"
49 //usage: "\n -m[FILE] Enter mount namespace"
50 //usage: "\n -u[FILE] Enter UTS namespace (hostname etc)"
51 //usage: "\n -i[FILE] Enter System V IPC namespace"
52 //usage: "\n -n[FILE] Enter network namespace"
53 //usage: "\n -p[FILE] Enter pid namespace"
54 //usage: "\n -U[FILE] Enter user namespace"
55 //usage: "\n -S UID Set uid in entered namespace"
56 //usage: "\n -G GID Set gid in entered namespace"
57 //usage: "\n -r[DIR] Set root directory"
58 //usage: "\n -w[DIR] Set working directory"
59 //usage: "\n -F Don't fork before exec'ing PROG"
64 # define CLONE_NEWUTS 0x04000000
67 # define CLONE_NEWIPC 0x08000000
70 # define CLONE_NEWUSER 0x10000000
73 # define CLONE_NEWPID 0x20000000
76 # define CLONE_NEWNET 0x40000000
81 struct namespace_descr {
82 int flag; /* value passed to setns() */
83 char ns_nsfile8[8]; /* "ns/" + namespace file in process' procfs entry */
86 struct namespace_ctx {
87 char *path; /* optional path to a custom ns file */
88 int fd; /* opened namespace file descriptor */
103 OPT_nofork = 1 << 11,
104 OPT_prescred = (1 << 12) * ENABLE_FEATURE_NSENTER_LONG_OPTS,
116 * The order is significant in nsenter.
117 * The user namespace comes first, so that it is entered first.
118 * This gives an unprivileged user the potential to enter other namespaces.
120 static const struct namespace_descr ns_list[] = {
121 { CLONE_NEWUSER, "ns/user", },
122 { CLONE_NEWIPC, "ns/ipc", },
123 { CLONE_NEWUTS, "ns/uts", },
124 { CLONE_NEWNET, "ns/net", },
125 { CLONE_NEWPID, "ns/pid", },
126 { CLONE_NEWNS, "ns/mnt", },
129 * Upstream nsenter doesn't support the short option for --preserve-credentials
131 static const char opt_str[] = "U::i::u::n::p::m::""t+S+G+r::w::F";
133 #if ENABLE_FEATURE_NSENTER_LONG_OPTS
134 static const char nsenter_longopts[] ALIGN1 =
135 "user\0" Optional_argument "U"
136 "ipc\0" Optional_argument "i"
137 "uts\0" Optional_argument "u"
138 "network\0" Optional_argument "n"
139 "pid\0" Optional_argument "p"
140 "mount\0" Optional_argument "m"
141 "target\0" Required_argument "t"
142 "setuid\0" Required_argument "S"
143 "setgid\0" Required_argument "G"
144 "root\0" Optional_argument "r"
145 "wd\0" Optional_argument "w"
146 "no-fork\0" No_argument "F"
147 "preserve-credentials\0" No_argument "\xff"
152 * Open a file and return the new descriptor. If a full path is provided in
153 * fs_path, then the file to which it points is opened. Otherwise (fd_path is
154 * NULL) the routine builds a path to a procfs file using the following
155 * template: '/proc/<target_pid>/<target_file>'.
157 static int open_by_path_or_target(const char *path,
158 pid_t target_pid, const char *target_file)
160 char proc_path_buf[sizeof("/proc/%u/1234567890") + sizeof(int)*3];
163 if (target_pid == 0) {
165 * "nsenter -p PROG" - neither -pFILE nor -tPID given.
169 snprintf(proc_path_buf, sizeof(proc_path_buf),
170 "/proc/%u/%s", (unsigned)target_pid, target_file);
171 path = proc_path_buf;
174 return xopen(path, O_RDONLY);
177 int nsenter_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
178 int nsenter_main(int argc UNUSED_PARAM, char **argv)
182 const char *root_dir_str = NULL;
183 const char *wd_str = NULL;
184 struct namespace_ctx ns_ctx_list[NS_COUNT];
185 int setgroups_failed;
191 memset(ns_ctx_list, 0, sizeof(ns_ctx_list));
193 IF_FEATURE_NSENTER_LONG_OPTS(applet_long_options = nsenter_longopts);
194 opts = getopt32(argv, opt_str,
195 &ns_ctx_list[NS_USR_POS].path,
196 &ns_ctx_list[NS_IPC_POS].path,
197 &ns_ctx_list[NS_UTS_POS].path,
198 &ns_ctx_list[NS_NET_POS].path,
199 &ns_ctx_list[NS_PID_POS].path,
200 &ns_ctx_list[NS_MNT_POS].path,
201 &target_pid, &uid, &gid,
202 &root_dir_str, &wd_str
206 root_fd = wd_fd = -1;
208 root_fd = open_by_path_or_target(root_dir_str,
211 wd_fd = open_by_path_or_target(wd_str, target_pid, "cwd");
213 for (i = 0; i < NS_COUNT; i++) {
214 const struct namespace_descr *ns = &ns_list[i];
215 struct namespace_ctx *ns_ctx = &ns_ctx_list[i];
219 ns_ctx->fd = open_by_path_or_target(ns_ctx->path,
220 target_pid, ns->ns_nsfile8);
224 * Entering the user namespace without --preserve-credentials implies
225 * --setuid & --setgid and clearing root's groups.
227 setgroups_failed = 0;
228 if ((opts & OPT_user) && !(opts & OPT_prescred)) {
229 opts |= (OPT_setuid | OPT_setgid);
231 * We call setgroups() before and after setns() and only
232 * bail-out if it fails twice.
234 setgroups_failed = (setgroups(0, NULL) < 0);
237 for (i = 0; i < NS_COUNT; i++) {
238 const struct namespace_descr *ns = &ns_list[i];
239 struct namespace_ctx *ns_ctx = &ns_ctx_list[i];
243 if (setns(ns_ctx->fd, ns->flag)) {
244 bb_perror_msg_and_die(
245 "setns(): can't reassociate to namespace '%s'",
246 ns->ns_nsfile8 + 3 /* skip over "ns/" */
249 close(ns_ctx->fd); /* should close fds, to not confuse exec'ed PROG */
256 * Save the current working directory if we're not
259 wd_fd = xopen(".", O_RDONLY);
274 * Entering the pid namespace implies forking unless it's been
275 * explicitly requested by the user not to.
277 if (!(opts & OPT_nofork) && (opts & OPT_pid)) {
278 xvfork_parent_waits_and_exits();
279 /* Child continues */
282 if (opts & OPT_setgid) {
283 if (setgroups(0, NULL) < 0 && setgroups_failed)
284 bb_perror_msg_and_die("setgroups");
287 if (opts & OPT_setuid)
290 exec_prog_or_SHELL(argv);