1 /* nsenter.c - Enter existing namespaces
2 *
3 * Copyright 2014 Andy Lutomirski <luto@amacapital.net>
4 *
5 * See http://man7.org/linux/man-pages/man1/nsenter.1.html
6 *
7 * unshare.c - run command in new context
8 *
9 * Copyright 2011 Rob Landley <rob@landley.net>
10 *
11 * See http://man7.org/linux/man-pages/man1/unshare.1.html
12 *
13
14 // Note: flags go in same order (right to left) for shared subset
15 USE_NSENTER(NEWTOY(nsenter, "<1F(no-fork)t#<1(target)i:(ipc);m:(mount);n:(net);p:(pid);u:(uts);U:(user);", TOYFLAG_USR|TOYFLAG_BIN))
16 USE_UNSHARE(NEWTOY(unshare, "<1^f(fork);r(map-root-user);i:(ipc);m:(mount);n:(net);p:(pid);u:(uts);U:(user);", TOYFLAG_USR|TOYFLAG_BIN))
17
18 config UNSHARE
19 bool "unshare"
20 default y
21 depends on TOYBOX_CONTAINER
22 help
23 usage: unshare [-imnpuUr] COMMAND...
24
25 Create new container namespace(s) for this process and its children, so
26 some attribute is not shared with the parent process.
27
28 -f Fork command in the background (--fork)
29 -i SysV IPC (message queues, semaphores, shared memory) (--ipc)
30 -m Mount/unmount tree (--mount)
31 -n Network address, sockets, routing, iptables (--net)
32 -p Process IDs and init (--pid)
33 -r Become root (map current euid/egid to 0/0, implies -U) (--map-root-user)
34 -u Host and domain names (--uts)
35 -U UIDs, GIDs, capabilities (--user)
36
37 A namespace allows a set of processes to have a different view of the
38 system than other sets of processes.
39
40 config NSENTER
41 bool "nsenter"
42 depends on TOYBOX_CONTAINER
43 default y
44 help
45 usage: nsenter [-t pid] [-F] [-i] [-m] [-n] [-p] [-u] [-U] COMMAND...
46
47 Run COMMAND in an existing (set of) namespace(s).
48
49 -t PID to take namespaces from (--target)
50 -F don't fork, even if -p is used (--no-fork)
51
52 The namespaces to switch are:
53
54 -i SysV IPC: message queues, semaphores, shared memory (--ipc)
55 -m Mount/unmount tree (--mount)
56 -n Network address, sockets, routing, iptables (--net)
57 -p Process IDs and init, will fork unless -F is used (--pid)
58 -u Host and domain names (--uts)
59 -U UIDs, GIDs, capabilities (--user)
60
61 If -t isn't specified, each namespace argument must provide a path
62 to a namespace file, ala "-i=/proc/$PID/ns/ipc"
63 */
64
65 #define FOR_nsenter
66 #include "toys.h"
67 #include <sys/syscall.h>
68 #include <linux/sched.h>
69
70 #define unshare(flags) syscall(SYS_unshare, flags)
71 #define setns(fd, nstype) syscall(SYS_setns, fd, nstype)
72
GLOBALS(char * Uupnmi[6];long t;)73 GLOBALS(
74 char *Uupnmi[6];
75 long t;
76 )
77
78 // Code that must run in unshare's flag context
79 #define CLEANUP_nsenter
80 #define FOR_unshare
81 #include <generated/flags.h>
82
83 static void write_ugid_map(char *map, unsigned eugid)
84 {
85 int bytes = sprintf(toybuf, "0 %u 1", eugid), fd = xopen(map, O_WRONLY);
86
87 xwrite(fd, toybuf, bytes);
88 xclose(fd);
89 }
90
handle_r(int euid,int egid)91 static void handle_r(int euid, int egid)
92 {
93 int fd;
94
95 if ((fd = open("/proc/self/setgroups", O_WRONLY)) >= 0) {
96 xwrite(fd, "deny", 4);
97 close(fd);
98 }
99
100 write_ugid_map("/proc/self/uid_map", euid);
101 write_ugid_map("/proc/self/gid_map", egid);
102 }
103
test_r()104 static int test_r()
105 {
106 return toys.optflags & FLAG_r;
107 }
108
test_f()109 static int test_f()
110 {
111 return toys.optflags & FLAG_f;
112 }
113
114 // Shift back to the context GLOBALS lives in (I.E. matching the filename).
115 #define CLEANUP_unshare
116 #define FOR_nsenter
117 #include <generated/flags.h>
118
unshare_main(void)119 void unshare_main(void)
120 {
121 unsigned flags[]={CLONE_NEWUSER, CLONE_NEWUTS, CLONE_NEWPID, CLONE_NEWNET,
122 CLONE_NEWNS, CLONE_NEWIPC}, f = 0;
123 int i, fd;
124
125 // Create new namespace(s)?
126 if (CFG_UNSHARE && *toys.which->name=='u') {
127 // For -r, we have to save our original [ug]id before calling unshare()
128 int euid = geteuid(), egid = getegid();
129
130 // unshare -U does not imply -r, so we cannot use [+rU]
131 if (test_r()) toys.optflags |= FLAG_U;
132
133 for (i = 0; i<ARRAY_LEN(flags); i++)
134 if (toys.optflags & (1<<i)) f |= flags[i];
135
136 if (unshare(f)) perror_exit(0);
137 if (test_r()) handle_r(euid, egid);
138
139 if (test_f()) {
140 toys.exitval = xrun(toys.optargs);
141
142 return;
143 }
144 // Bind to existing namespace(s)?
145 } else if (CFG_NSENTER) {
146 char *nsnames = "user\0uts\0pid\0net\0mnt\0ipc";
147
148 for (i = 0; i<ARRAY_LEN(flags); i++) {
149 char *filename = TT.Uupnmi[i];
150
151 if (toys.optflags & (1<<i)) {
152 if (!filename || !*filename) {
153 if (!(toys.optflags & FLAG_t)) error_exit("need -t or =filename");
154 sprintf(toybuf, "/proc/%ld/ns/%s", TT.t, nsnames);
155 filename = toybuf;
156 }
157
158 if (setns(fd = xopenro(filename), flags[i])) perror_exit("setns");
159 close(fd);
160 }
161 nsnames += strlen(nsnames)+1;
162 }
163
164 if ((toys.optflags & FLAG_p) && !(toys.optflags & FLAG_F)) {
165 toys.exitval = xrun(toys.optargs);
166
167 return;
168 }
169 }
170
171 xexec(toys.optargs);
172 }
173
nsenter_main(void)174 void nsenter_main(void)
175 {
176 unshare_main();
177 }
178