summaryrefslogtreecommitdiffstats
path: root/man2/ioctl_ns.2
blob: a11e54b9b70647d3d91d305aa27a31bb2d69980e (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
.\" Copyright (c) 2017 by Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\"
.TH ioctl_ns 2 2023-05-03 "Linux man-pages 6.05.01"
.SH NAME
ioctl_ns \- ioctl() operations for Linux namespaces
.SH DESCRIPTION
.\" ============================================================
.\"
.SS Discovering namespace relationships
The following
.BR ioctl (2)
operations are provided to allow discovery of namespace relationships (see
.BR user_namespaces (7)
and
.BR pid_namespaces (7)).
The form of the calls is:
.PP
.in +4n
.EX
new_fd = ioctl(fd, request);
.EE
.in
.PP
In each case,
.I fd
refers to a
.IR /proc/ pid /ns/*
file.
Both operations return a new file descriptor on success.
.TP
.BR NS_GET_USERNS " (since Linux 4.9)"
.\" commit bcac25a58bfc6bd79191ac5d7afb49bea96da8c9
.\" commit 6786741dbf99e44fb0c0ed85a37582b8a26f1c3b
Returns a file descriptor that refers to the owning user namespace
for the namespace referred to by
.IR fd .
.TP
.BR NS_GET_PARENT " (since Linux 4.9)"
.\" commit a7306ed8d94af729ecef8b6e37506a1c6fc14788
Returns a file descriptor that refers to the parent namespace of
the namespace referred to by
.IR fd .
This operation is valid only for hierarchical namespaces
(i.e., PID and user namespaces).
For user namespaces,
.B NS_GET_PARENT
is synonymous with
.BR NS_GET_USERNS .
.PP
The new file descriptor returned by these operations is opened with the
.B O_RDONLY
and
.B O_CLOEXEC
(close-on-exec; see
.BR fcntl (2))
flags.
.PP
By applying
.BR fstat (2)
to the returned file descriptor, one obtains a
.I stat
structure whose
.I st_dev
(resident device) and
.I st_ino
(inode number) fields together identify the owning/parent namespace.
This inode number can be matched with the inode number of another
.IR /proc/ pid /ns/ { pid , user }
file to determine whether that is the owning/parent namespace.
.PP
Either of these
.BR ioctl (2)
operations can fail with the following errors:
.TP
.B EPERM
The requested namespace is outside of the caller's namespace scope.
This error can occur if, for example, the owning user namespace is an
ancestor of the caller's current user namespace.
It can also occur on attempts to obtain the parent of the initial
user or PID namespace.
.TP
.B ENOTTY
The operation is not supported by this kernel version.
.PP
Additionally, the
.B NS_GET_PARENT
operation can fail with the following error:
.TP
.B EINVAL
.I fd
refers to a nonhierarchical namespace.
.PP
See the EXAMPLES section for an example of the use of these operations.
.\" ============================================================
.\"
.SS Discovering the namespace type
The
.B NS_GET_NSTYPE
.\" commit e5ff5ce6e20ee22511398bb31fb912466cf82a36
operation (available since Linux 4.11) can be used to discover
the type of namespace referred to by the file descriptor
.IR fd :
.PP
.in +4n
.EX
nstype = ioctl(fd, NS_GET_NSTYPE);
.EE
.in
.PP
.I fd
refers to a
.IR /proc/ pid /ns/*
file.
.PP
The return value is one of the
.B CLONE_NEW*
values that can be specified to
.BR clone (2)
or
.BR unshare (2)
in order to create a namespace.
.\" ============================================================
.\"
.SS Discovering the owner of a user namespace
The
.B NS_GET_OWNER_UID
.\" commit 015bb305b8ebe8d601a238ab70ebdc394c7a19ba
operation (available since Linux 4.11) can be used to discover
the owner user ID of a user namespace (i.e., the effective user ID
of the process that created the user namespace).
The form of the call is:
.PP
.in +4n
.EX
uid_t uid;
ioctl(fd, NS_GET_OWNER_UID, &uid);
.EE
.in
.PP
.I fd
refers to a
.IR /proc/ pid /ns/user
file.
.PP
The owner user ID is returned in the
.I uid_t
pointed to by the third argument.
.PP
This operation can fail with the following error:
.TP
.B EINVAL
.I fd
does not refer to a user namespace.
.SH ERRORS
Any of the above
.BR ioctl ()
operations can return the following errors:
.TP
.B ENOTTY
.I fd
does not refer to a
.IR /proc/ pid /ns/ *
file.
.SH STANDARDS
Linux.
.SH EXAMPLES
The example shown below uses the
.BR ioctl (2)
operations described above to perform simple
discovery of namespace relationships.
The following shell sessions show various examples of the use
of this program.
.PP
Trying to get the parent of the initial user namespace fails,
since it has no parent:
.PP
.in +4n
.EX
$ \fB./ns_show /proc/self/ns/user p\fP
The parent namespace is outside your namespace scope
.EE
.in
.PP
Create a process running
.BR sleep (1)
that resides in new user and UTS namespaces,
and show that the new UTS namespace is associated with the new user namespace:
.PP
.in +4n
.EX
$ \fBunshare \-Uu sleep 1000 &\fP
[1] 23235
$ \fB./ns_show /proc/23235/ns/uts u\fP
Device/Inode of owning user namespace is: [0,3] / 4026532448
$ \fBreadlink /proc/23235/ns/user\fP
user:[4026532448]
.EE
.in
.PP
Then show that the parent of the new user namespace in the preceding
example is the initial user namespace:
.PP
.in +4n
.EX
$ \fBreadlink /proc/self/ns/user\fP
user:[4026531837]
$ \fB./ns_show /proc/23235/ns/user p\fP
Device/Inode of parent namespace is: [0,3] / 4026531837
.EE
.in
.PP
Start a shell in a new user namespace, and show that from within
this shell, the parent user namespace can't be discovered.
Similarly, the UTS namespace
(which is associated with the initial user namespace)
can't be discovered.
.PP
.in +4n
.EX
$ \fBPS1="sh2$ " unshare \-U bash\fP
sh2$ \fB./ns_show /proc/self/ns/user p\fP
The parent namespace is outside your namespace scope
sh2$ \fB./ns_show /proc/self/ns/uts u\fP
The owning user namespace is outside your namespace scope
.EE
.in
.SS Program source
\&
.\" SRC BEGIN (ns_show.c)
.EX
/* ns_show.c
\&
   Licensed under the GNU General Public License v2 or later.
*/
#include <errno.h>
#include <fcntl.h>
#include <linux/nsfs.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/sysmacros.h>
#include <unistd.h>
\&
int
main(int argc, char *argv[])
{
    int          fd, userns_fd, parent_fd;
    struct stat  sb;
\&
    if (argc < 2) {
        fprintf(stderr, "Usage: %s /proc/[pid]/ns/[file] [p|u]\en",
                argv[0]);
        fprintf(stderr, "\enDisplay the result of one or both "
                "of NS_GET_USERNS (u) or NS_GET_PARENT (p)\en"
                "for the specified /proc/[pid]/ns/[file]. If neither "
                "\[aq]p\[aq] nor \[aq]u\[aq] is specified,\en"
                "NS_GET_USERNS is the default.\en");
        exit(EXIT_FAILURE);
    }
\&
    /* Obtain a file descriptor for the \[aq]ns\[aq] file specified
       in argv[1]. */
\&
    fd = open(argv[1], O_RDONLY);
    if (fd == \-1) {
        perror("open");
        exit(EXIT_FAILURE);
    }
\&
    /* Obtain a file descriptor for the owning user namespace and
       then obtain and display the inode number of that namespace. */
\&
    if (argc < 3 || strchr(argv[2], \[aq]u\[aq])) {
        userns_fd = ioctl(fd, NS_GET_USERNS);
\&
        if (userns_fd == \-1) {
            if (errno == EPERM)
                printf("The owning user namespace is outside "
                       "your namespace scope\en");
            else
               perror("ioctl\-NS_GET_USERNS");
            exit(EXIT_FAILURE);
         }
\&
        if (fstat(userns_fd, &sb) == \-1) {
            perror("fstat\-userns");
            exit(EXIT_FAILURE);
        }
        printf("Device/Inode of owning user namespace is: "
               "[%x,%x] / %ju\en",
               major(sb.st_dev),
               minor(sb.st_dev),
               (uintmax_t) sb.st_ino);
\&
        close(userns_fd);
    }
\&
    /* Obtain a file descriptor for the parent namespace and
       then obtain and display the inode number of that namespace. */
\&
    if (argc > 2 && strchr(argv[2], \[aq]p\[aq])) {
        parent_fd = ioctl(fd, NS_GET_PARENT);
\&
        if (parent_fd == \-1) {
            if (errno == EINVAL)
                printf("Can\[aq] get parent namespace of a "
                       "nonhierarchical namespace\en");
            else if (errno == EPERM)
                printf("The parent namespace is outside "
                       "your namespace scope\en");
            else
                perror("ioctl\-NS_GET_PARENT");
            exit(EXIT_FAILURE);
        }
\&
        if (fstat(parent_fd, &sb) == \-1) {
            perror("fstat\-parentns");
            exit(EXIT_FAILURE);
        }
        printf("Device/Inode of parent namespace is: [%x,%x] / %ju\en",
               major(sb.st_dev),
               minor(sb.st_dev),
               (uintmax_t) sb.st_ino);
\&
        close(parent_fd);
    }
\&
    exit(EXIT_SUCCESS);
}
.EE
.\" SRC END
.SH SEE ALSO
.BR fstat (2),
.BR ioctl (2),
.BR proc (5),
.BR namespaces (7)