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1 | /* Linux namespaces(7) support. |
2 | ||
3 | Copyright (C) 2015 Free Software Foundation, Inc. | |
4 | ||
5 | This file is part of GDB. | |
6 | ||
7 | This program is free software; you can redistribute it and/or modify | |
8 | it under the terms of the GNU General Public License as published by | |
9 | the Free Software Foundation; either version 3 of the License, or | |
10 | (at your option) any later version. | |
11 | ||
12 | This program is distributed in the hope that it will be useful, | |
13 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
14 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
15 | GNU General Public License for more details. | |
16 | ||
17 | You should have received a copy of the GNU General Public License | |
18 | along with this program. If not, see <http://www.gnu.org/licenses/>. */ | |
19 | ||
20 | #include "common-defs.h" | |
21 | #include "nat/linux-namespaces.h" | |
22 | #include "filestuff.h" | |
23 | #include <fcntl.h> | |
24 | #include <sys/syscall.h> | |
25 | #include <sys/types.h> | |
26 | #include <sys/stat.h> | |
27 | #include <sys/socket.h> | |
198c808c | 28 | #include "gdb_wait.h" |
4b8b5e72 GB |
29 | #include <signal.h> |
30 | #include <sched.h> | |
31 | ||
32 | /* See nat/linux-namespaces.h. */ | |
33 | int debug_linux_namespaces; | |
34 | ||
35 | /* Handle systems without setns. */ | |
36 | ||
37 | #ifndef HAVE_SETNS | |
38 | static int | |
39 | setns (int fd, int nstype) | |
40 | { | |
41 | #ifdef __NR_setns | |
42 | return syscall (__NR_setns, fd, nstype); | |
43 | #else | |
44 | errno = ENOSYS; | |
45 | return -1; | |
46 | #endif | |
47 | } | |
48 | #endif | |
49 | ||
50 | /* A Linux namespace. */ | |
51 | ||
52 | struct linux_ns | |
53 | { | |
54 | /* Filename of this namespace's entries in /proc/PID/ns. */ | |
55 | const char *filename; | |
56 | ||
57 | /* Nonzero if this object has been initialized. */ | |
58 | int initialized; | |
59 | ||
60 | /* Nonzero if this namespace is supported on this system. */ | |
61 | int supported; | |
62 | ||
63 | /* ID of the namespace the calling process is in, used to | |
64 | see if other processes share the namespace. The code in | |
65 | this file assumes that the calling process never changes | |
66 | namespace. */ | |
67 | ino_t id; | |
68 | }; | |
69 | ||
70 | /* Return the absolute filename of process PID's /proc/PID/ns | |
71 | entry for namespace NS. The returned value persists until | |
72 | this function is next called. */ | |
73 | ||
74 | static const char * | |
75 | linux_ns_filename (struct linux_ns *ns, int pid) | |
76 | { | |
77 | static char filename[PATH_MAX]; | |
78 | ||
79 | gdb_assert (pid > 0); | |
80 | xsnprintf (filename, sizeof (filename), "/proc/%d/ns/%s", pid, | |
81 | ns->filename); | |
82 | ||
83 | return filename; | |
84 | } | |
85 | ||
86 | /* Return a representation of the caller's TYPE namespace, or | |
87 | NULL if TYPE namespaces are not supported on this system. */ | |
88 | ||
89 | static struct linux_ns * | |
90 | linux_ns_get_namespace (enum linux_ns_type type) | |
91 | { | |
92 | static struct linux_ns namespaces[NUM_LINUX_NS_TYPES] = | |
93 | { | |
94 | { "ipc" }, | |
95 | { "mnt" }, | |
96 | { "net" }, | |
97 | { "pid" }, | |
98 | { "user" }, | |
99 | { "uts" }, | |
100 | }; | |
101 | struct linux_ns *ns; | |
102 | ||
103 | gdb_assert (type >= 0 && type < NUM_LINUX_NS_TYPES); | |
104 | ns = &namespaces[type]; | |
105 | ||
106 | if (!ns->initialized) | |
107 | { | |
108 | struct stat sb; | |
109 | ||
110 | if (stat (linux_ns_filename (ns, getpid ()), &sb) == 0) | |
111 | { | |
112 | ns->id = sb.st_ino; | |
113 | ||
114 | ns->supported = 1; | |
115 | } | |
116 | ||
117 | ns->initialized = 1; | |
118 | } | |
119 | ||
120 | return ns->supported ? ns : NULL; | |
121 | } | |
122 | ||
123 | /* See nat/linux-namespaces.h. */ | |
124 | ||
125 | int | |
126 | linux_ns_same (pid_t pid, enum linux_ns_type type) | |
127 | { | |
128 | struct linux_ns *ns = linux_ns_get_namespace (type); | |
129 | const char *filename; | |
130 | struct stat sb; | |
131 | ||
132 | /* If the kernel does not support TYPE namespaces then there's | |
133 | effectively only one TYPE namespace that all processes on | |
134 | the system share. */ | |
135 | if (ns == NULL) | |
136 | return 1; | |
137 | ||
138 | /* Stat PID's TYPE namespace entry to get the namespace ID. This | |
139 | might fail if the process died, or if we don't have the right | |
140 | permissions (though we should be attached by this time so this | |
141 | seems unlikely). In any event, we can't make any decisions and | |
142 | must throw. */ | |
143 | filename = linux_ns_filename (ns, pid); | |
144 | if (stat (filename, &sb) != 0) | |
145 | perror_with_name (filename); | |
146 | ||
147 | return sb.st_ino == ns->id; | |
148 | } | |
149 | ||
150 | /* We need to use setns(2) to handle filesystem access in mount | |
151 | namespaces other than our own, but this isn't permitted for | |
152 | multithreaded processes. GDB is multithreaded when compiled | |
153 | with Guile support, and may become multithreaded if compiled | |
154 | with Python support. We deal with this by spawning a single- | |
155 | threaded helper process to access mount namespaces other than | |
156 | our own. | |
157 | ||
158 | The helper process is started the first time a call to setns | |
159 | is required. The main process (GDB or gdbserver) communicates | |
160 | with the helper via sockets, passing file descriptors where | |
161 | necessary using SCM_RIGHTS. Once started the helper process | |
162 | runs until the main process terminates; when this happens the | |
163 | helper will receive socket errors, notice that its parent died, | |
164 | and exit accordingly (see mnsh_maybe_mourn_peer). | |
165 | ||
166 | The protocol is that the main process sends a request in a | |
167 | single message, and the helper replies to every message it | |
168 | receives with a single-message response. If the helper | |
169 | receives a message it does not understand it will reply with | |
170 | a MNSH_MSG_ERROR message. The main process checks all | |
171 | responses it receives with gdb_assert, so if the main process | |
172 | receives something unexpected (which includes MNSH_MSG_ERROR) | |
173 | the main process will call internal_error. | |
174 | ||
175 | For avoidance of doubt, if the helper process receives a | |
176 | message it doesn't handle it will reply with MNSH_MSG_ERROR. | |
177 | If the main process receives MNSH_MSG_ERROR at any time then | |
178 | it will call internal_error. If internal_error causes the | |
179 | main process to exit, the helper will notice this and also | |
180 | exit. The helper will not exit until the main process | |
181 | terminates, so if the user continues through internal_error | |
182 | the helper will still be there awaiting requests from the | |
183 | main process. | |
184 | ||
185 | Messages in both directions have the following payload: | |
186 | ||
187 | - TYPE (enum mnsh_msg_type, always sent) - the message type. | |
188 | - INT1 and | |
189 | - INT2 (int, always sent, though not always used) - two | |
190 | values whose meaning is message-type-dependent. | |
191 | See enum mnsh_msg_type documentation below. | |
192 | - FD (int, optional, sent using SCM_RIGHTS) - an open file | |
193 | descriptor. | |
194 | - BUF (unstructured data, optional) - some data with message- | |
195 | type-dependent meaning. | |
196 | ||
197 | Note that the helper process is the child of a call to fork, | |
198 | so all code in the helper must be async-signal-safe. */ | |
199 | ||
200 | /* Mount namespace helper message types. */ | |
201 | ||
202 | enum mnsh_msg_type | |
203 | { | |
204 | /* A communication error occurred. Receipt of this message | |
205 | by either end will cause an assertion failure in the main | |
206 | process. */ | |
207 | MNSH_MSG_ERROR, | |
208 | ||
209 | /* Requests, sent from the main process to the helper. */ | |
210 | ||
211 | /* A request that the helper call setns. Arguments should | |
212 | be passed in FD and INT1. Helper should respond with a | |
213 | MNSH_RET_INT. */ | |
214 | MNSH_REQ_SETNS, | |
215 | ||
216 | /* A request that the helper call open. Arguments should | |
217 | be passed in BUF, INT1 and INT2. The filename (in BUF) | |
218 | should include a terminating NUL character. The helper | |
219 | should respond with a MNSH_RET_FD. */ | |
220 | MNSH_REQ_OPEN, | |
221 | ||
222 | /* A request that the helper call unlink. The single | |
223 | argument (the filename) should be passed in BUF, and | |
224 | should include a terminating NUL character. The helper | |
225 | should respond with a MNSH_RET_INT. */ | |
226 | MNSH_REQ_UNLINK, | |
227 | ||
228 | /* A request that the helper call readlink. The single | |
229 | argument (the filename) should be passed in BUF, and | |
230 | should include a terminating NUL character. The helper | |
231 | should respond with a MNSH_RET_INTSTR. */ | |
232 | MNSH_REQ_READLINK, | |
233 | ||
234 | /* Responses, sent to the main process from the helper. */ | |
235 | ||
236 | /* Return an integer in INT1 and errno in INT2. */ | |
237 | MNSH_RET_INT, | |
238 | ||
239 | /* Return a file descriptor in FD if one was opened or an | |
240 | integer in INT1 otherwise. Return errno in INT2. */ | |
241 | MNSH_RET_FD, | |
242 | ||
243 | /* Return an integer in INT1, errno in INT2, and optionally | |
244 | some data in BUF. */ | |
245 | MNSH_RET_INTSTR, | |
246 | }; | |
247 | ||
248 | /* Print a string representation of a message using debug_printf. | |
249 | This function is not async-signal-safe so should never be | |
250 | called from the helper. */ | |
251 | ||
252 | static void | |
253 | mnsh_debug_print_message (enum mnsh_msg_type type, | |
254 | int fd, int int1, int int2, | |
255 | const void *buf, int bufsiz) | |
256 | { | |
257 | gdb_byte *c = (gdb_byte *) buf; | |
258 | gdb_byte *cl = c + bufsiz; | |
259 | ||
260 | switch (type) | |
261 | { | |
262 | case MNSH_MSG_ERROR: | |
263 | debug_printf ("ERROR"); | |
264 | break; | |
265 | ||
266 | case MNSH_REQ_SETNS: | |
267 | debug_printf ("SETNS"); | |
268 | break; | |
269 | ||
270 | case MNSH_REQ_OPEN: | |
271 | debug_printf ("OPEN"); | |
272 | break; | |
273 | ||
274 | case MNSH_REQ_UNLINK: | |
275 | debug_printf ("UNLINK"); | |
276 | break; | |
277 | ||
278 | case MNSH_REQ_READLINK: | |
279 | debug_printf ("READLINK"); | |
280 | break; | |
281 | ||
282 | case MNSH_RET_INT: | |
283 | debug_printf ("INT"); | |
284 | break; | |
285 | ||
286 | case MNSH_RET_FD: | |
287 | debug_printf ("FD"); | |
288 | break; | |
289 | ||
290 | case MNSH_RET_INTSTR: | |
291 | debug_printf ("INTSTR"); | |
292 | break; | |
293 | ||
294 | default: | |
295 | debug_printf ("unknown-packet-%d", type); | |
296 | } | |
297 | ||
298 | debug_printf (" %d %d %d \"", fd, int1, int2); | |
299 | ||
300 | for (; c < cl; c++) | |
301 | debug_printf (*c >= ' ' && *c <= '~' ? "%c" : "\\%o", *c); | |
302 | ||
303 | debug_printf ("\""); | |
304 | } | |
305 | ||
306 | /* Forward declaration. */ | |
307 | ||
308 | static void mnsh_maybe_mourn_peer (void); | |
309 | ||
310 | /* Send a message. The argument SOCK is the file descriptor of the | |
311 | sending socket, the other arguments are the payload to send. | |
312 | Return the number of bytes sent on success. Return -1 on failure | |
313 | and set errno appropriately. This function is called by both the | |
314 | main process and the helper so must be async-signal-safe. */ | |
315 | ||
316 | static ssize_t | |
317 | mnsh_send_message (int sock, enum mnsh_msg_type type, | |
318 | int fd, int int1, int int2, | |
319 | const void *buf, int bufsiz) | |
320 | { | |
321 | struct msghdr msg; | |
322 | struct iovec iov[4]; | |
323 | char fdbuf[CMSG_SPACE (sizeof (fd))]; | |
324 | ssize_t size; | |
325 | ||
326 | /* Build the basic TYPE, INT1, INT2 message. */ | |
327 | memset (&msg, 0, sizeof (msg)); | |
328 | msg.msg_iov = iov; | |
329 | ||
330 | iov[0].iov_base = &type; | |
331 | iov[0].iov_len = sizeof (type); | |
332 | iov[1].iov_base = &int1; | |
333 | iov[1].iov_len = sizeof (int1); | |
334 | iov[2].iov_base = &int2; | |
335 | iov[2].iov_len = sizeof (int2); | |
336 | ||
337 | msg.msg_iovlen = 3; | |
338 | ||
339 | /* Append BUF if supplied. */ | |
340 | if (buf != NULL && bufsiz > 0) | |
341 | { | |
342 | iov[3].iov_base = alloca (bufsiz); | |
343 | memcpy (iov[3].iov_base, buf, bufsiz); | |
344 | iov[3].iov_len = bufsiz; | |
345 | ||
346 | msg.msg_iovlen ++; | |
347 | } | |
348 | ||
349 | /* Attach FD if supplied. */ | |
350 | if (fd >= 0) | |
351 | { | |
352 | struct cmsghdr *cmsg; | |
353 | ||
354 | msg.msg_control = fdbuf; | |
355 | msg.msg_controllen = sizeof (fdbuf); | |
356 | ||
357 | cmsg = CMSG_FIRSTHDR (&msg); | |
358 | cmsg->cmsg_level = SOL_SOCKET; | |
359 | cmsg->cmsg_type = SCM_RIGHTS; | |
360 | cmsg->cmsg_len = CMSG_LEN (sizeof (int)); | |
361 | ||
362 | memcpy (CMSG_DATA (cmsg), &fd, sizeof (int)); | |
363 | ||
364 | msg.msg_controllen = cmsg->cmsg_len; | |
365 | } | |
366 | ||
367 | /* Send the message. */ | |
368 | size = sendmsg (sock, &msg, 0); | |
369 | ||
370 | if (size < 0) | |
371 | mnsh_maybe_mourn_peer (); | |
372 | ||
373 | if (debug_linux_namespaces) | |
374 | { | |
375 | debug_printf ("mnsh: send: "); | |
376 | mnsh_debug_print_message (type, fd, int1, int2, buf, bufsiz); | |
6449ed0d | 377 | debug_printf (" -> %s\n", pulongest (size)); |
4b8b5e72 GB |
378 | } |
379 | ||
380 | return size; | |
381 | } | |
382 | ||
383 | /* Receive a message. The argument SOCK is the file descriptor of | |
384 | the receiving socket, the other arguments point to storage for | |
385 | the received payload. Returns the number of bytes stored into | |
386 | BUF on success, which may be zero in the event no BUF was sent. | |
387 | Return -1 on failure and set errno appropriately. This function | |
388 | is called from both the main process and the helper and must be | |
389 | async-signal-safe. */ | |
390 | ||
391 | static ssize_t | |
392 | mnsh_recv_message (int sock, enum mnsh_msg_type *type, | |
393 | int *fd, int *int1, int *int2, | |
394 | void *buf, int bufsiz) | |
395 | { | |
396 | struct msghdr msg; | |
397 | struct iovec iov[4]; | |
398 | char fdbuf[CMSG_SPACE (sizeof (*fd))]; | |
399 | struct cmsghdr *cmsg; | |
400 | ssize_t size, fixed_size; | |
401 | int i; | |
402 | ||
403 | /* Build the message to receive data into. */ | |
404 | memset (&msg, 0, sizeof (msg)); | |
405 | msg.msg_iov = iov; | |
406 | ||
407 | iov[0].iov_base = type; | |
408 | iov[0].iov_len = sizeof (*type); | |
409 | iov[1].iov_base = int1; | |
410 | iov[1].iov_len = sizeof (*int1); | |
411 | iov[2].iov_base = int2; | |
412 | iov[2].iov_len = sizeof (*int2); | |
413 | iov[3].iov_base = buf; | |
414 | iov[3].iov_len = bufsiz; | |
415 | ||
416 | msg.msg_iovlen = 4; | |
417 | ||
418 | for (fixed_size = i = 0; i < msg.msg_iovlen - 1; i++) | |
419 | fixed_size += iov[i].iov_len; | |
420 | ||
421 | msg.msg_control = fdbuf; | |
422 | msg.msg_controllen = sizeof (fdbuf); | |
423 | ||
424 | /* Receive the message. */ | |
425 | size = recvmsg (sock, &msg, MSG_CMSG_CLOEXEC); | |
426 | if (size < 0) | |
427 | { | |
428 | if (debug_linux_namespaces) | |
6449ed0d GB |
429 | debug_printf ("namespace-helper: recv failed (%s)\n", |
430 | pulongest (size)); | |
4b8b5e72 GB |
431 | |
432 | mnsh_maybe_mourn_peer (); | |
433 | ||
434 | return size; | |
435 | } | |
436 | ||
437 | /* Check for truncation. */ | |
438 | if (size < fixed_size || (msg.msg_flags & (MSG_TRUNC | MSG_CTRUNC))) | |
439 | { | |
440 | if (debug_linux_namespaces) | |
6449ed0d GB |
441 | debug_printf ("namespace-helper: recv truncated (%s 0x%x)\n", |
442 | pulongest (size), msg.msg_flags); | |
4b8b5e72 GB |
443 | |
444 | mnsh_maybe_mourn_peer (); | |
445 | ||
446 | errno = EBADMSG; | |
447 | return -1; | |
448 | } | |
449 | ||
450 | /* Unpack the file descriptor if supplied. */ | |
451 | cmsg = CMSG_FIRSTHDR (&msg); | |
452 | if (cmsg != NULL | |
453 | && cmsg->cmsg_len == CMSG_LEN (sizeof (int)) | |
454 | && cmsg->cmsg_level == SOL_SOCKET | |
455 | && cmsg->cmsg_type == SCM_RIGHTS) | |
456 | memcpy (fd, CMSG_DATA (cmsg), sizeof (int)); | |
457 | else | |
458 | *fd = -1; | |
459 | ||
460 | if (debug_linux_namespaces) | |
461 | { | |
462 | debug_printf ("mnsh: recv: "); | |
463 | mnsh_debug_print_message (*type, *fd, *int1, *int2, buf, | |
464 | size - fixed_size); | |
465 | debug_printf ("\n"); | |
466 | } | |
467 | ||
468 | /* Return the number of bytes of data in BUF. */ | |
469 | return size - fixed_size; | |
470 | } | |
471 | ||
472 | /* Shortcuts for returning results from the helper. */ | |
473 | ||
474 | #define mnsh_return_int(sock, result, error) \ | |
475 | mnsh_send_message (sock, MNSH_RET_INT, -1, result, error, NULL, 0) | |
476 | ||
477 | #define mnsh_return_fd(sock, fd, error) \ | |
478 | mnsh_send_message (sock, MNSH_RET_FD, \ | |
479 | (fd) < 0 ? -1 : (fd), \ | |
480 | (fd) < 0 ? (fd) : 0, \ | |
481 | error, NULL, 0) | |
482 | ||
483 | #define mnsh_return_intstr(sock, result, buf, bufsiz, error) \ | |
484 | mnsh_send_message (sock, MNSH_RET_INTSTR, -1, result, error, \ | |
485 | buf, bufsiz) | |
486 | ||
487 | /* Handle a MNSH_REQ_SETNS message. Must be async-signal-safe. */ | |
488 | ||
489 | static ssize_t | |
490 | mnsh_handle_setns (int sock, int fd, int nstype) | |
491 | { | |
492 | int result = setns (fd, nstype); | |
493 | ||
494 | return mnsh_return_int (sock, result, errno); | |
495 | } | |
496 | ||
497 | /* Handle a MNSH_REQ_OPEN message. Must be async-signal-safe. */ | |
498 | ||
499 | static ssize_t | |
500 | mnsh_handle_open (int sock, const char *filename, | |
501 | int flags, mode_t mode) | |
502 | { | |
503 | int fd = gdb_open_cloexec (filename, flags, mode); | |
504 | ssize_t result = mnsh_return_fd (sock, fd, errno); | |
505 | ||
506 | if (fd >= 0) | |
507 | close (fd); | |
508 | ||
509 | return result; | |
510 | } | |
511 | ||
512 | /* Handle a MNSH_REQ_UNLINK message. Must be async-signal-safe. */ | |
513 | ||
514 | static ssize_t | |
515 | mnsh_handle_unlink (int sock, const char *filename) | |
516 | { | |
517 | int result = unlink (filename); | |
518 | ||
519 | return mnsh_return_int (sock, result, errno); | |
520 | } | |
521 | ||
522 | /* Handle a MNSH_REQ_READLINK message. Must be async-signal-safe. */ | |
523 | ||
524 | static ssize_t | |
525 | mnsh_handle_readlink (int sock, const char *filename) | |
526 | { | |
527 | char buf[PATH_MAX]; | |
528 | int len = readlink (filename, buf, sizeof (buf)); | |
529 | ||
530 | return mnsh_return_intstr (sock, len, | |
531 | buf, len < 0 ? 0 : len, | |
532 | errno); | |
533 | } | |
534 | ||
535 | /* The helper process. Never returns. Must be async-signal-safe. */ | |
536 | ||
537 | static void mnsh_main (int sock) ATTRIBUTE_NORETURN; | |
538 | ||
539 | static void | |
540 | mnsh_main (int sock) | |
541 | { | |
542 | while (1) | |
543 | { | |
544 | enum mnsh_msg_type type; | |
545 | int fd, int1, int2; | |
546 | char buf[PATH_MAX]; | |
547 | ssize_t size, response = -1; | |
548 | ||
549 | size = mnsh_recv_message (sock, &type, | |
550 | &fd, &int1, &int2, | |
551 | buf, sizeof (buf)); | |
552 | ||
553 | if (size >= 0 && size < sizeof (buf)) | |
554 | { | |
555 | switch (type) | |
556 | { | |
557 | case MNSH_REQ_SETNS: | |
558 | if (fd > 0) | |
559 | response = mnsh_handle_setns (sock, fd, int1); | |
560 | break; | |
561 | ||
562 | case MNSH_REQ_OPEN: | |
563 | if (size > 0 && buf[size - 1] == '\0') | |
564 | response = mnsh_handle_open (sock, buf, int1, int2); | |
565 | break; | |
566 | ||
567 | case MNSH_REQ_UNLINK: | |
568 | if (size > 0 && buf[size - 1] == '\0') | |
569 | response = mnsh_handle_unlink (sock, buf); | |
570 | break; | |
571 | ||
572 | case MNSH_REQ_READLINK: | |
573 | if (size > 0 && buf[size - 1] == '\0') | |
574 | response = mnsh_handle_readlink (sock, buf); | |
575 | break; | |
576 | ||
577 | default: | |
578 | break; /* Handled below. */ | |
579 | } | |
580 | } | |
581 | ||
582 | /* Close any file descriptors we were passed. */ | |
583 | if (fd >= 0) | |
584 | close (fd); | |
585 | ||
586 | /* Can't handle this message, bounce it back. */ | |
587 | if (response < 0) | |
588 | { | |
589 | if (size < 0) | |
590 | size = 0; | |
591 | ||
592 | mnsh_send_message (sock, MNSH_MSG_ERROR, | |
593 | -1, int1, int2, buf, size); | |
594 | } | |
595 | } | |
596 | } | |
597 | ||
598 | /* The mount namespace helper process. */ | |
599 | ||
600 | struct linux_mnsh | |
601 | { | |
602 | /* PID of helper. */ | |
603 | pid_t pid; | |
604 | ||
605 | /* Socket for communication. */ | |
606 | int sock; | |
607 | ||
608 | /* ID of the mount namespace the helper is currently in. */ | |
609 | ino_t nsid; | |
610 | }; | |
611 | ||
612 | /* In the helper process this is set to the PID of the process that | |
613 | created the helper (i.e. GDB or gdbserver). In the main process | |
614 | this is set to zero. Used by mnsh_maybe_mourn_peer. */ | |
615 | static int mnsh_creator_pid = 0; | |
616 | ||
617 | /* Return an object representing the mount namespace helper process. | |
618 | If no mount namespace helper process has been started then start | |
619 | one. Return NULL if no mount namespace helper process could be | |
620 | started. */ | |
621 | ||
622 | static struct linux_mnsh * | |
623 | linux_mntns_get_helper (void) | |
624 | { | |
625 | static struct linux_mnsh *helper = NULL; | |
626 | ||
627 | if (helper == NULL) | |
628 | { | |
629 | static struct linux_mnsh h; | |
630 | struct linux_ns *ns; | |
631 | pid_t helper_creator = getpid (); | |
632 | int sv[2]; | |
633 | ||
634 | ns = linux_ns_get_namespace (LINUX_NS_MNT); | |
635 | if (ns == NULL) | |
636 | return NULL; | |
637 | ||
638 | if (gdb_socketpair_cloexec (AF_UNIX, SOCK_STREAM, 0, sv) < 0) | |
639 | return NULL; | |
640 | ||
641 | h.pid = fork (); | |
642 | if (h.pid < 0) | |
643 | { | |
644 | int saved_errno = errno; | |
645 | ||
646 | close (sv[0]); | |
647 | close (sv[1]); | |
648 | ||
649 | errno = saved_errno; | |
650 | return NULL; | |
651 | } | |
652 | ||
653 | if (h.pid == 0) | |
654 | { | |
655 | /* Child process. */ | |
656 | close (sv[0]); | |
657 | ||
658 | mnsh_creator_pid = helper_creator; | |
659 | ||
660 | /* Debug printing isn't async-signal-safe. */ | |
661 | debug_linux_namespaces = 0; | |
662 | ||
663 | mnsh_main (sv[1]); | |
664 | } | |
665 | ||
666 | /* Parent process. */ | |
667 | close (sv[1]); | |
668 | ||
669 | helper = &h; | |
670 | helper->sock = sv[0]; | |
671 | helper->nsid = ns->id; | |
672 | ||
673 | if (debug_linux_namespaces) | |
674 | debug_printf ("Started mount namespace helper process %d\n", | |
675 | helper->pid); | |
676 | } | |
677 | ||
678 | return helper; | |
679 | } | |
680 | ||
681 | /* Check whether the other process died and act accordingly. Called | |
682 | whenever a socket error occurs, from both the main process and the | |
683 | helper. Must be async-signal-safe when called from the helper. */ | |
684 | ||
685 | static void | |
686 | mnsh_maybe_mourn_peer (void) | |
687 | { | |
688 | if (mnsh_creator_pid != 0) | |
689 | { | |
690 | /* We're in the helper. Check if our current parent is the | |
691 | process that started us. If it isn't, then our original | |
692 | parent died and we've been reparented. Exit immediately | |
693 | if that's the case. */ | |
694 | if (getppid () != mnsh_creator_pid) | |
695 | _exit (0); | |
696 | } | |
697 | else | |
698 | { | |
699 | /* We're in the main process. */ | |
700 | ||
701 | struct linux_mnsh *helper = linux_mntns_get_helper (); | |
702 | int status; | |
703 | pid_t pid; | |
704 | ||
705 | if (helper->pid < 0) | |
706 | { | |
707 | /* We already mourned it. */ | |
708 | return; | |
709 | } | |
710 | ||
711 | pid = waitpid (helper->pid, &status, WNOHANG); | |
712 | if (pid == 0) | |
713 | { | |
714 | /* The helper is still alive. */ | |
715 | return; | |
716 | } | |
717 | else if (pid == -1) | |
718 | { | |
719 | if (errno == ECHILD) | |
720 | warning (_("mount namespace helper vanished?")); | |
721 | else | |
722 | internal_warning (__FILE__, __LINE__, | |
723 | _("unhandled error %d"), errno); | |
724 | } | |
725 | else if (pid == helper->pid) | |
726 | { | |
727 | if (WIFEXITED (status)) | |
728 | warning (_("mount namespace helper exited with status %d"), | |
729 | WEXITSTATUS (status)); | |
730 | else if (WIFSIGNALED (status)) | |
731 | warning (_("mount namespace helper killed by signal %d"), | |
732 | WTERMSIG (status)); | |
733 | else | |
734 | internal_warning (__FILE__, __LINE__, | |
735 | _("unhandled status %d"), status); | |
736 | } | |
737 | else | |
738 | internal_warning (__FILE__, __LINE__, | |
739 | _("unknown pid %d"), pid); | |
740 | ||
741 | /* Something unrecoverable happened. */ | |
742 | helper->pid = -1; | |
743 | } | |
744 | } | |
745 | ||
746 | /* Shortcuts for sending messages to the helper. */ | |
747 | ||
748 | #define mnsh_send_setns(helper, fd, nstype) \ | |
749 | mnsh_send_message (helper->sock, MNSH_REQ_SETNS, fd, nstype, 0, \ | |
750 | NULL, 0) | |
751 | ||
752 | #define mnsh_send_open(helper, filename, flags, mode) \ | |
753 | mnsh_send_message (helper->sock, MNSH_REQ_OPEN, -1, flags, mode, \ | |
754 | filename, strlen (filename) + 1) | |
755 | ||
756 | #define mnsh_send_unlink(helper, filename) \ | |
757 | mnsh_send_message (helper->sock, MNSH_REQ_UNLINK, -1, 0, 0, \ | |
758 | filename, strlen (filename) + 1) | |
759 | ||
760 | #define mnsh_send_readlink(helper, filename) \ | |
761 | mnsh_send_message (helper->sock, MNSH_REQ_READLINK, -1, 0, 0, \ | |
762 | filename, strlen (filename) + 1) | |
763 | ||
764 | /* Receive a message from the helper. Issue an assertion failure if | |
765 | the message isn't a correctly-formatted MNSH_RET_INT. Set RESULT | |
766 | and ERROR and return 0 on success. Set errno and return -1 on | |
767 | failure. */ | |
768 | ||
769 | static int | |
770 | mnsh_recv_int (struct linux_mnsh *helper, int *result, int *error) | |
771 | { | |
772 | enum mnsh_msg_type type; | |
773 | char buf[PATH_MAX]; | |
774 | ssize_t size; | |
775 | int fd; | |
776 | ||
777 | size = mnsh_recv_message (helper->sock, &type, &fd, | |
778 | result, error, | |
779 | buf, sizeof (buf)); | |
780 | if (size < 0) | |
781 | return -1; | |
782 | ||
783 | gdb_assert (type == MNSH_RET_INT); | |
784 | gdb_assert (fd == -1); | |
785 | gdb_assert (size == 0); | |
786 | ||
787 | return 0; | |
788 | } | |
789 | ||
790 | /* Receive a message from the helper. Issue an assertion failure if | |
791 | the message isn't a correctly-formatted MNSH_RET_FD. Set FD and | |
792 | ERROR and return 0 on success. Set errno and return -1 on | |
793 | failure. */ | |
794 | ||
795 | static int | |
796 | mnsh_recv_fd (struct linux_mnsh *helper, int *fd, int *error) | |
797 | { | |
798 | enum mnsh_msg_type type; | |
799 | char buf[PATH_MAX]; | |
800 | ssize_t size; | |
801 | int result; | |
802 | ||
803 | size = mnsh_recv_message (helper->sock, &type, fd, | |
804 | &result, error, | |
805 | buf, sizeof (buf)); | |
806 | if (size < 0) | |
807 | return -1; | |
808 | ||
809 | gdb_assert (type == MNSH_RET_FD); | |
810 | gdb_assert (size == 0); | |
811 | ||
812 | if (*fd < 0) | |
813 | { | |
814 | gdb_assert (result < 0); | |
815 | *fd = result; | |
816 | } | |
817 | ||
818 | return 0; | |
819 | } | |
820 | ||
821 | /* Receive a message from the helper. Issue an assertion failure if | |
822 | the message isn't a correctly-formatted MNSH_RET_INTSTR. Set | |
823 | RESULT and ERROR and optionally store data in BUF, then return | |
824 | the number of bytes stored in BUF on success (this may be zero). | |
825 | Set errno and return -1 on error. */ | |
826 | ||
827 | static ssize_t | |
828 | mnsh_recv_intstr (struct linux_mnsh *helper, | |
829 | int *result, int *error, | |
830 | void *buf, int bufsiz) | |
831 | { | |
832 | enum mnsh_msg_type type; | |
833 | ssize_t size; | |
834 | int fd; | |
835 | ||
836 | size = mnsh_recv_message (helper->sock, &type, &fd, | |
837 | result, error, | |
838 | buf, bufsiz); | |
839 | ||
840 | if (size < 0) | |
841 | return -1; | |
842 | ||
843 | gdb_assert (type == MNSH_RET_INTSTR); | |
844 | gdb_assert (fd == -1); | |
845 | ||
846 | return size; | |
847 | } | |
848 | ||
849 | /* Return values for linux_mntns_access_fs. */ | |
850 | ||
851 | enum mnsh_fs_code | |
852 | { | |
853 | /* Something went wrong, errno is set. */ | |
854 | MNSH_FS_ERROR = -1, | |
855 | ||
856 | /* The main process is in the correct mount namespace. | |
857 | The caller should access the filesystem directly. */ | |
858 | MNSH_FS_DIRECT, | |
859 | ||
860 | /* The helper is in the correct mount namespace. | |
861 | The caller should access the filesystem via the helper. */ | |
862 | MNSH_FS_HELPER | |
863 | }; | |
864 | ||
865 | /* Return a value indicating how the caller should access the | |
866 | mount namespace of process PID. */ | |
867 | ||
868 | static enum mnsh_fs_code | |
869 | linux_mntns_access_fs (pid_t pid) | |
870 | { | |
871 | struct cleanup *old_chain; | |
872 | struct linux_ns *ns; | |
873 | struct stat sb; | |
874 | struct linux_mnsh *helper; | |
875 | ssize_t size; | |
876 | int fd, saved_errno; | |
877 | ||
878 | if (pid == getpid ()) | |
879 | return MNSH_FS_DIRECT; | |
880 | ||
881 | ns = linux_ns_get_namespace (LINUX_NS_MNT); | |
882 | if (ns == NULL) | |
883 | return MNSH_FS_DIRECT; | |
884 | ||
885 | old_chain = make_cleanup (null_cleanup, NULL); | |
886 | ||
887 | fd = gdb_open_cloexec (linux_ns_filename (ns, pid), O_RDONLY, 0); | |
888 | if (fd < 0) | |
889 | goto error; | |
890 | ||
891 | old_chain = make_cleanup_close (fd); | |
892 | ||
893 | if (fstat (fd, &sb) != 0) | |
894 | goto error; | |
895 | ||
896 | if (sb.st_ino == ns->id) | |
897 | { | |
898 | do_cleanups (old_chain); | |
899 | ||
900 | return MNSH_FS_DIRECT; | |
901 | } | |
902 | ||
903 | helper = linux_mntns_get_helper (); | |
904 | if (helper == NULL) | |
905 | goto error; | |
906 | ||
907 | if (sb.st_ino != helper->nsid) | |
908 | { | |
909 | int result, error; | |
910 | ||
911 | size = mnsh_send_setns (helper, fd, 0); | |
912 | if (size < 0) | |
913 | goto error; | |
914 | ||
915 | if (mnsh_recv_int (helper, &result, &error) != 0) | |
916 | goto error; | |
917 | ||
918 | if (result != 0) | |
919 | { | |
920 | /* ENOSYS indicates that an entire function is unsupported | |
921 | (it's not appropriate for our versions of open/unlink/ | |
922 | readlink to sometimes return with ENOSYS depending on how | |
923 | they're called) so we convert ENOSYS to ENOTSUP if setns | |
924 | fails. */ | |
925 | if (error == ENOSYS) | |
926 | error = ENOTSUP; | |
927 | ||
928 | errno = error; | |
929 | goto error; | |
930 | } | |
931 | ||
932 | helper->nsid = sb.st_ino; | |
933 | } | |
934 | ||
935 | do_cleanups (old_chain); | |
936 | ||
937 | return MNSH_FS_HELPER; | |
938 | ||
939 | error: | |
940 | saved_errno = errno; | |
941 | ||
942 | do_cleanups (old_chain); | |
943 | ||
944 | errno = saved_errno; | |
945 | return MNSH_FS_ERROR; | |
946 | } | |
947 | ||
948 | /* See nat/linux-namespaces.h. */ | |
949 | ||
950 | int | |
951 | linux_mntns_open_cloexec (pid_t pid, const char *filename, | |
952 | int flags, mode_t mode) | |
953 | { | |
954 | enum mnsh_fs_code access = linux_mntns_access_fs (pid); | |
955 | struct linux_mnsh *helper; | |
956 | int fd, error; | |
957 | ssize_t size; | |
958 | ||
959 | if (access == MNSH_FS_ERROR) | |
960 | return -1; | |
961 | ||
962 | if (access == MNSH_FS_DIRECT) | |
963 | return gdb_open_cloexec (filename, flags, mode); | |
964 | ||
965 | gdb_assert (access == MNSH_FS_HELPER); | |
966 | ||
967 | helper = linux_mntns_get_helper (); | |
968 | ||
969 | size = mnsh_send_open (helper, filename, flags, mode); | |
970 | if (size < 0) | |
971 | return -1; | |
972 | ||
973 | if (mnsh_recv_fd (helper, &fd, &error) != 0) | |
974 | return -1; | |
975 | ||
976 | if (fd < 0) | |
977 | errno = error; | |
978 | ||
979 | return fd; | |
980 | } | |
981 | ||
982 | /* See nat/linux-namespaces.h. */ | |
983 | ||
984 | int | |
985 | linux_mntns_unlink (pid_t pid, const char *filename) | |
986 | { | |
987 | enum mnsh_fs_code access = linux_mntns_access_fs (pid); | |
988 | struct linux_mnsh *helper; | |
989 | int ret, error; | |
990 | ssize_t size; | |
991 | ||
992 | if (access == MNSH_FS_ERROR) | |
993 | return -1; | |
994 | ||
995 | if (access == MNSH_FS_DIRECT) | |
996 | return unlink (filename); | |
997 | ||
998 | gdb_assert (access == MNSH_FS_HELPER); | |
999 | ||
1000 | helper = linux_mntns_get_helper (); | |
1001 | ||
1002 | size = mnsh_send_unlink (helper, filename); | |
1003 | if (size < 0) | |
1004 | return -1; | |
1005 | ||
1006 | if (mnsh_recv_int (helper, &ret, &error) != 0) | |
1007 | return -1; | |
1008 | ||
1009 | if (ret != 0) | |
1010 | errno = error; | |
1011 | ||
1012 | return ret; | |
1013 | } | |
1014 | ||
1015 | /* See nat/linux-namespaces.h. */ | |
1016 | ||
1017 | ssize_t | |
1018 | linux_mntns_readlink (pid_t pid, const char *filename, | |
1019 | char *buf, size_t bufsiz) | |
1020 | { | |
1021 | enum mnsh_fs_code access = linux_mntns_access_fs (pid); | |
1022 | struct linux_mnsh *helper; | |
1023 | int ret, error; | |
1024 | ssize_t size; | |
1025 | ||
1026 | if (access == MNSH_FS_ERROR) | |
1027 | return -1; | |
1028 | ||
1029 | if (access == MNSH_FS_DIRECT) | |
1030 | return readlink (filename, buf, bufsiz); | |
1031 | ||
1032 | gdb_assert (access == MNSH_FS_HELPER); | |
1033 | ||
1034 | helper = linux_mntns_get_helper (); | |
1035 | ||
1036 | size = mnsh_send_readlink (helper, filename); | |
1037 | if (size < 0) | |
1038 | return -1; | |
1039 | ||
1040 | size = mnsh_recv_intstr (helper, &ret, &error, buf, bufsiz); | |
1041 | ||
1042 | if (size < 0) | |
1043 | { | |
1044 | ret = -1; | |
1045 | errno = error; | |
1046 | } | |
1047 | else | |
1048 | gdb_assert (size == ret); | |
1049 | ||
1050 | return ret; | |
1051 | } |