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-rw-r--r--util-linux/nsenter.c291
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diff --git a/util-linux/nsenter.c b/util-linux/nsenter.c
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1/* vi: set sw=4 ts=4: */
2/*
3 * Mini nsenter implementation for busybox.
4 *
5 * Copyright (C) 2016 by Bartosz Golaszewski <bartekgola@gmail.com>
6 *
7 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
8 */
9
10//config:config NSENTER
11//config: bool "nsenter"
12//config: default y
13//config: select PLATFORM_LINUX
14//config: help
15//config: Run program with namespaces of other processes.
16//config:
17//config:config FEATURE_NSENTER_LONG_OPTS
18//config: bool "Enable long options"
19//config: default y
20//config: depends on NSENTER && LONG_OPTS
21//config: help
22//config: Support long options for the nsenter applet. This makes
23//config: the busybox implementation more compatible with upstream.
24
25//applet:IF_NSENTER(APPLET(nsenter, BB_DIR_USR_BIN, BB_SUID_DROP))
26
27//kbuild:lib-$(CONFIG_NSENTER) += nsenter.o
28
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"
46//usage:#else
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"
60//usage:#endif
61
62#include <sched.h>
63#ifndef CLONE_NEWUTS
64# define CLONE_NEWUTS 0x04000000
65#endif
66#ifndef CLONE_NEWIPC
67# define CLONE_NEWIPC 0x08000000
68#endif
69#ifndef CLONE_NEWUSER
70# define CLONE_NEWUSER 0x10000000
71#endif
72#ifndef CLONE_NEWPID
73# define CLONE_NEWPID 0x20000000
74#endif
75#ifndef CLONE_NEWNET
76# define CLONE_NEWNET 0x40000000
77#endif
78
79#include "libbb.h"
80
81struct namespace_descr {
82 int flag; /* value passed to setns() */
83 char ns_nsfile8[8]; /* "ns/" + namespace file in process' procfs entry */
84};
85
86struct namespace_ctx {
87 char *path; /* optional path to a custom ns file */
88 int fd; /* opened namespace file descriptor */
89};
90
91enum {
92 OPT_user = 1 << 0,
93 OPT_ipc = 1 << 1,
94 OPT_uts = 1 << 2,
95 OPT_network = 1 << 3,
96 OPT_pid = 1 << 4,
97 OPT_mount = 1 << 5,
98 OPT_target = 1 << 6,
99 OPT_setuid = 1 << 7,
100 OPT_setgid = 1 << 8,
101 OPT_root = 1 << 9,
102 OPT_wd = 1 << 10,
103 OPT_nofork = 1 << 11,
104 OPT_prescred = (1 << 12) * ENABLE_FEATURE_NSENTER_LONG_OPTS,
105};
106enum {
107 NS_USR_POS = 0,
108 NS_IPC_POS,
109 NS_UTS_POS,
110 NS_NET_POS,
111 NS_PID_POS,
112 NS_MNT_POS,
113 NS_COUNT,
114};
115/*
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.
119 */
120static 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", },
127};
128/*
129 * Upstream nsenter doesn't support the short option for --preserve-credentials
130 */
131static const char opt_str[] = "U::i::u::n::p::m::""t+S+G+r::w::F";
132
133#if ENABLE_FEATURE_NSENTER_LONG_OPTS
134static 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"
148 ;
149#endif
150
151/*
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>'.
156 */
157static int open_by_path_or_target(const char *path,
158 pid_t target_pid, const char *target_file)
159{
160 char proc_path_buf[sizeof("/proc/%u/1234567890") + sizeof(int)*3];
161
162 if (!path) {
163 if (target_pid == 0) {
164 /* Example:
165 * "nsenter -p PROG" - neither -pFILE nor -tPID given.
166 */
167 bb_show_usage();
168 }
169 snprintf(proc_path_buf, sizeof(proc_path_buf),
170 "/proc/%u/%s", (unsigned)target_pid, target_file);
171 path = proc_path_buf;
172 }
173
174 return xopen(path, O_RDONLY);
175}
176
177int nsenter_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
178int nsenter_main(int argc UNUSED_PARAM, char **argv)
179{
180 int i;
181 unsigned int opts;
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;
186 int root_fd, wd_fd;
187 int target_pid = 0;
188 int uid = 0;
189 int gid = 0;
190
191 memset(ns_ctx_list, 0, sizeof(ns_ctx_list));
192
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
203 );
204 argv += optind;
205
206 root_fd = wd_fd = -1;
207 if (opts & OPT_root)
208 root_fd = open_by_path_or_target(root_dir_str,
209 target_pid, "root");
210 if (opts & OPT_wd)
211 wd_fd = open_by_path_or_target(wd_str, target_pid, "cwd");
212
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];
216
217 ns_ctx->fd = -1;
218 if (opts & (1 << i))
219 ns_ctx->fd = open_by_path_or_target(ns_ctx->path,
220 target_pid, ns->ns_nsfile8);
221 }
222
223 /*
224 * Entering the user namespace without --preserve-credentials implies
225 * --setuid & --setgid and clearing root's groups.
226 */
227 setgroups_failed = 0;
228 if ((opts & OPT_user) && !(opts & OPT_prescred)) {
229 opts |= (OPT_setuid | OPT_setgid);
230 /*
231 * We call setgroups() before and after setns() and only
232 * bail-out if it fails twice.
233 */
234 setgroups_failed = (setgroups(0, NULL) < 0);
235 }
236
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];
240
241 if (ns_ctx->fd < 0)
242 continue;
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/" */
247 );
248 }
249 close(ns_ctx->fd); /* should close fds, to not confuse exec'ed PROG */
250 /*ns_ctx->fd = -1;*/
251 }
252
253 if (root_fd >= 0) {
254 if (wd_fd < 0) {
255 /*
256 * Save the current working directory if we're not
257 * changing it.
258 */
259 wd_fd = xopen(".", O_RDONLY);
260 }
261 xfchdir(root_fd);
262 xchroot(".");
263 close(root_fd);
264 /*root_fd = -1;*/
265 }
266
267 if (wd_fd >= 0) {
268 xfchdir(wd_fd);
269 close(wd_fd);
270 /*wd_fd = -1;*/
271 }
272
273 /*
274 * Entering the pid namespace implies forking unless it's been
275 * explicitly requested by the user not to.
276 */
277 if (!(opts & OPT_nofork) && (opts & OPT_pid)) {
278 xvfork_parent_waits_and_exits();
279 /* Child continues */
280 }
281
282 if (opts & OPT_setgid) {
283 if (setgroups(0, NULL) < 0 && setgroups_failed)
284 bb_perror_msg_and_die("setgroups");
285 xsetgid(gid);
286 }
287 if (opts & OPT_setuid)
288 xsetuid(uid);
289
290 exec_prog_or_SHELL(argv);
291}
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