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4b8b5e72 GB |
1 | /* Linux namespaces(7) support. |
2 | ||
61baf725 | 3 | Copyright (C) 2015-2017 Free Software Foundation, Inc. |
4b8b5e72 GB |
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 | ||
eb0edac8 GB |
35 | /* Handle systems without fork. */ |
36 | ||
37 | static inline pid_t | |
38 | do_fork (void) | |
39 | { | |
40 | #ifdef HAVE_FORK | |
41 | return fork (); | |
42 | #else | |
43 | errno = ENOSYS; | |
44 | return -1; | |
45 | #endif | |
46 | } | |
47 | ||
4b8b5e72 GB |
48 | /* Handle systems without setns. */ |
49 | ||
99fe86f7 PB |
50 | static inline int |
51 | do_setns (int fd, int nstype) | |
4b8b5e72 | 52 | { |
99fe86f7 PB |
53 | #ifdef HAVE_SETNS |
54 | return setns (fd, nstype); | |
55 | #elif defined __NR_setns | |
4b8b5e72 GB |
56 | return syscall (__NR_setns, fd, nstype); |
57 | #else | |
58 | errno = ENOSYS; | |
59 | return -1; | |
60 | #endif | |
61 | } | |
4b8b5e72 | 62 | |
4da680ad ME |
63 | /* Handle systems without MSG_CMSG_CLOEXEC. */ |
64 | ||
65 | #ifndef MSG_CMSG_CLOEXEC | |
66 | #define MSG_CMSG_CLOEXEC 0 | |
67 | #endif | |
68 | ||
4b8b5e72 GB |
69 | /* A Linux namespace. */ |
70 | ||
71 | struct linux_ns | |
72 | { | |
73 | /* Filename of this namespace's entries in /proc/PID/ns. */ | |
74 | const char *filename; | |
75 | ||
76 | /* Nonzero if this object has been initialized. */ | |
77 | int initialized; | |
78 | ||
79 | /* Nonzero if this namespace is supported on this system. */ | |
80 | int supported; | |
81 | ||
82 | /* ID of the namespace the calling process is in, used to | |
83 | see if other processes share the namespace. The code in | |
84 | this file assumes that the calling process never changes | |
85 | namespace. */ | |
86 | ino_t id; | |
87 | }; | |
88 | ||
89 | /* Return the absolute filename of process PID's /proc/PID/ns | |
90 | entry for namespace NS. The returned value persists until | |
91 | this function is next called. */ | |
92 | ||
93 | static const char * | |
94 | linux_ns_filename (struct linux_ns *ns, int pid) | |
95 | { | |
96 | static char filename[PATH_MAX]; | |
97 | ||
98 | gdb_assert (pid > 0); | |
99 | xsnprintf (filename, sizeof (filename), "/proc/%d/ns/%s", pid, | |
100 | ns->filename); | |
101 | ||
102 | return filename; | |
103 | } | |
104 | ||
105 | /* Return a representation of the caller's TYPE namespace, or | |
106 | NULL if TYPE namespaces are not supported on this system. */ | |
107 | ||
108 | static struct linux_ns * | |
109 | linux_ns_get_namespace (enum linux_ns_type type) | |
110 | { | |
111 | static struct linux_ns namespaces[NUM_LINUX_NS_TYPES] = | |
112 | { | |
113 | { "ipc" }, | |
114 | { "mnt" }, | |
115 | { "net" }, | |
116 | { "pid" }, | |
117 | { "user" }, | |
118 | { "uts" }, | |
119 | }; | |
120 | struct linux_ns *ns; | |
121 | ||
122 | gdb_assert (type >= 0 && type < NUM_LINUX_NS_TYPES); | |
123 | ns = &namespaces[type]; | |
124 | ||
125 | if (!ns->initialized) | |
126 | { | |
127 | struct stat sb; | |
128 | ||
129 | if (stat (linux_ns_filename (ns, getpid ()), &sb) == 0) | |
130 | { | |
131 | ns->id = sb.st_ino; | |
132 | ||
133 | ns->supported = 1; | |
134 | } | |
135 | ||
136 | ns->initialized = 1; | |
137 | } | |
138 | ||
139 | return ns->supported ? ns : NULL; | |
140 | } | |
141 | ||
142 | /* See nat/linux-namespaces.h. */ | |
143 | ||
144 | int | |
145 | linux_ns_same (pid_t pid, enum linux_ns_type type) | |
146 | { | |
147 | struct linux_ns *ns = linux_ns_get_namespace (type); | |
148 | const char *filename; | |
149 | struct stat sb; | |
150 | ||
151 | /* If the kernel does not support TYPE namespaces then there's | |
152 | effectively only one TYPE namespace that all processes on | |
153 | the system share. */ | |
154 | if (ns == NULL) | |
155 | return 1; | |
156 | ||
157 | /* Stat PID's TYPE namespace entry to get the namespace ID. This | |
158 | might fail if the process died, or if we don't have the right | |
159 | permissions (though we should be attached by this time so this | |
160 | seems unlikely). In any event, we can't make any decisions and | |
161 | must throw. */ | |
162 | filename = linux_ns_filename (ns, pid); | |
163 | if (stat (filename, &sb) != 0) | |
164 | perror_with_name (filename); | |
165 | ||
166 | return sb.st_ino == ns->id; | |
167 | } | |
168 | ||
169 | /* We need to use setns(2) to handle filesystem access in mount | |
170 | namespaces other than our own, but this isn't permitted for | |
171 | multithreaded processes. GDB is multithreaded when compiled | |
172 | with Guile support, and may become multithreaded if compiled | |
173 | with Python support. We deal with this by spawning a single- | |
174 | threaded helper process to access mount namespaces other than | |
175 | our own. | |
176 | ||
177 | The helper process is started the first time a call to setns | |
178 | is required. The main process (GDB or gdbserver) communicates | |
179 | with the helper via sockets, passing file descriptors where | |
180 | necessary using SCM_RIGHTS. Once started the helper process | |
181 | runs until the main process terminates; when this happens the | |
182 | helper will receive socket errors, notice that its parent died, | |
183 | and exit accordingly (see mnsh_maybe_mourn_peer). | |
184 | ||
185 | The protocol is that the main process sends a request in a | |
186 | single message, and the helper replies to every message it | |
187 | receives with a single-message response. If the helper | |
188 | receives a message it does not understand it will reply with | |
189 | a MNSH_MSG_ERROR message. The main process checks all | |
190 | responses it receives with gdb_assert, so if the main process | |
191 | receives something unexpected (which includes MNSH_MSG_ERROR) | |
192 | the main process will call internal_error. | |
193 | ||
194 | For avoidance of doubt, if the helper process receives a | |
195 | message it doesn't handle it will reply with MNSH_MSG_ERROR. | |
196 | If the main process receives MNSH_MSG_ERROR at any time then | |
197 | it will call internal_error. If internal_error causes the | |
198 | main process to exit, the helper will notice this and also | |
199 | exit. The helper will not exit until the main process | |
200 | terminates, so if the user continues through internal_error | |
201 | the helper will still be there awaiting requests from the | |
202 | main process. | |
203 | ||
204 | Messages in both directions have the following payload: | |
205 | ||
206 | - TYPE (enum mnsh_msg_type, always sent) - the message type. | |
207 | - INT1 and | |
208 | - INT2 (int, always sent, though not always used) - two | |
209 | values whose meaning is message-type-dependent. | |
210 | See enum mnsh_msg_type documentation below. | |
211 | - FD (int, optional, sent using SCM_RIGHTS) - an open file | |
212 | descriptor. | |
213 | - BUF (unstructured data, optional) - some data with message- | |
214 | type-dependent meaning. | |
215 | ||
216 | Note that the helper process is the child of a call to fork, | |
217 | so all code in the helper must be async-signal-safe. */ | |
218 | ||
219 | /* Mount namespace helper message types. */ | |
220 | ||
221 | enum mnsh_msg_type | |
222 | { | |
223 | /* A communication error occurred. Receipt of this message | |
224 | by either end will cause an assertion failure in the main | |
225 | process. */ | |
226 | MNSH_MSG_ERROR, | |
227 | ||
228 | /* Requests, sent from the main process to the helper. */ | |
229 | ||
230 | /* A request that the helper call setns. Arguments should | |
231 | be passed in FD and INT1. Helper should respond with a | |
232 | MNSH_RET_INT. */ | |
233 | MNSH_REQ_SETNS, | |
234 | ||
235 | /* A request that the helper call open. Arguments should | |
236 | be passed in BUF, INT1 and INT2. The filename (in BUF) | |
237 | should include a terminating NUL character. The helper | |
238 | should respond with a MNSH_RET_FD. */ | |
239 | MNSH_REQ_OPEN, | |
240 | ||
241 | /* A request that the helper call unlink. The single | |
242 | argument (the filename) should be passed in BUF, and | |
243 | should include a terminating NUL character. The helper | |
244 | should respond with a MNSH_RET_INT. */ | |
245 | MNSH_REQ_UNLINK, | |
246 | ||
247 | /* A request that the helper call readlink. The single | |
248 | argument (the filename) should be passed in BUF, and | |
249 | should include a terminating NUL character. The helper | |
250 | should respond with a MNSH_RET_INTSTR. */ | |
251 | MNSH_REQ_READLINK, | |
252 | ||
253 | /* Responses, sent to the main process from the helper. */ | |
254 | ||
255 | /* Return an integer in INT1 and errno in INT2. */ | |
256 | MNSH_RET_INT, | |
257 | ||
258 | /* Return a file descriptor in FD if one was opened or an | |
259 | integer in INT1 otherwise. Return errno in INT2. */ | |
260 | MNSH_RET_FD, | |
261 | ||
262 | /* Return an integer in INT1, errno in INT2, and optionally | |
263 | some data in BUF. */ | |
264 | MNSH_RET_INTSTR, | |
265 | }; | |
266 | ||
267 | /* Print a string representation of a message using debug_printf. | |
268 | This function is not async-signal-safe so should never be | |
269 | called from the helper. */ | |
270 | ||
271 | static void | |
272 | mnsh_debug_print_message (enum mnsh_msg_type type, | |
273 | int fd, int int1, int int2, | |
274 | const void *buf, int bufsiz) | |
275 | { | |
276 | gdb_byte *c = (gdb_byte *) buf; | |
277 | gdb_byte *cl = c + bufsiz; | |
278 | ||
279 | switch (type) | |
280 | { | |
281 | case MNSH_MSG_ERROR: | |
282 | debug_printf ("ERROR"); | |
283 | break; | |
284 | ||
285 | case MNSH_REQ_SETNS: | |
286 | debug_printf ("SETNS"); | |
287 | break; | |
288 | ||
289 | case MNSH_REQ_OPEN: | |
290 | debug_printf ("OPEN"); | |
291 | break; | |
292 | ||
293 | case MNSH_REQ_UNLINK: | |
294 | debug_printf ("UNLINK"); | |
295 | break; | |
296 | ||
297 | case MNSH_REQ_READLINK: | |
298 | debug_printf ("READLINK"); | |
299 | break; | |
300 | ||
301 | case MNSH_RET_INT: | |
302 | debug_printf ("INT"); | |
303 | break; | |
304 | ||
305 | case MNSH_RET_FD: | |
306 | debug_printf ("FD"); | |
307 | break; | |
308 | ||
309 | case MNSH_RET_INTSTR: | |
310 | debug_printf ("INTSTR"); | |
311 | break; | |
312 | ||
313 | default: | |
314 | debug_printf ("unknown-packet-%d", type); | |
315 | } | |
316 | ||
317 | debug_printf (" %d %d %d \"", fd, int1, int2); | |
318 | ||
319 | for (; c < cl; c++) | |
320 | debug_printf (*c >= ' ' && *c <= '~' ? "%c" : "\\%o", *c); | |
321 | ||
322 | debug_printf ("\""); | |
323 | } | |
324 | ||
325 | /* Forward declaration. */ | |
326 | ||
327 | static void mnsh_maybe_mourn_peer (void); | |
328 | ||
329 | /* Send a message. The argument SOCK is the file descriptor of the | |
330 | sending socket, the other arguments are the payload to send. | |
331 | Return the number of bytes sent on success. Return -1 on failure | |
332 | and set errno appropriately. This function is called by both the | |
333 | main process and the helper so must be async-signal-safe. */ | |
334 | ||
335 | static ssize_t | |
336 | mnsh_send_message (int sock, enum mnsh_msg_type type, | |
337 | int fd, int int1, int int2, | |
338 | const void *buf, int bufsiz) | |
339 | { | |
340 | struct msghdr msg; | |
341 | struct iovec iov[4]; | |
342 | char fdbuf[CMSG_SPACE (sizeof (fd))]; | |
343 | ssize_t size; | |
344 | ||
345 | /* Build the basic TYPE, INT1, INT2 message. */ | |
346 | memset (&msg, 0, sizeof (msg)); | |
347 | msg.msg_iov = iov; | |
348 | ||
349 | iov[0].iov_base = &type; | |
350 | iov[0].iov_len = sizeof (type); | |
351 | iov[1].iov_base = &int1; | |
352 | iov[1].iov_len = sizeof (int1); | |
353 | iov[2].iov_base = &int2; | |
354 | iov[2].iov_len = sizeof (int2); | |
355 | ||
356 | msg.msg_iovlen = 3; | |
357 | ||
358 | /* Append BUF if supplied. */ | |
359 | if (buf != NULL && bufsiz > 0) | |
360 | { | |
361 | iov[3].iov_base = alloca (bufsiz); | |
362 | memcpy (iov[3].iov_base, buf, bufsiz); | |
363 | iov[3].iov_len = bufsiz; | |
364 | ||
365 | msg.msg_iovlen ++; | |
366 | } | |
367 | ||
368 | /* Attach FD if supplied. */ | |
369 | if (fd >= 0) | |
370 | { | |
371 | struct cmsghdr *cmsg; | |
372 | ||
373 | msg.msg_control = fdbuf; | |
374 | msg.msg_controllen = sizeof (fdbuf); | |
375 | ||
376 | cmsg = CMSG_FIRSTHDR (&msg); | |
377 | cmsg->cmsg_level = SOL_SOCKET; | |
378 | cmsg->cmsg_type = SCM_RIGHTS; | |
379 | cmsg->cmsg_len = CMSG_LEN (sizeof (int)); | |
380 | ||
381 | memcpy (CMSG_DATA (cmsg), &fd, sizeof (int)); | |
382 | ||
383 | msg.msg_controllen = cmsg->cmsg_len; | |
384 | } | |
385 | ||
386 | /* Send the message. */ | |
387 | size = sendmsg (sock, &msg, 0); | |
388 | ||
389 | if (size < 0) | |
390 | mnsh_maybe_mourn_peer (); | |
391 | ||
392 | if (debug_linux_namespaces) | |
393 | { | |
394 | debug_printf ("mnsh: send: "); | |
395 | mnsh_debug_print_message (type, fd, int1, int2, buf, bufsiz); | |
6449ed0d | 396 | debug_printf (" -> %s\n", pulongest (size)); |
4b8b5e72 GB |
397 | } |
398 | ||
399 | return size; | |
400 | } | |
401 | ||
402 | /* Receive a message. The argument SOCK is the file descriptor of | |
403 | the receiving socket, the other arguments point to storage for | |
404 | the received payload. Returns the number of bytes stored into | |
405 | BUF on success, which may be zero in the event no BUF was sent. | |
406 | Return -1 on failure and set errno appropriately. This function | |
407 | is called from both the main process and the helper and must be | |
408 | async-signal-safe. */ | |
409 | ||
410 | static ssize_t | |
411 | mnsh_recv_message (int sock, enum mnsh_msg_type *type, | |
412 | int *fd, int *int1, int *int2, | |
413 | void *buf, int bufsiz) | |
414 | { | |
415 | struct msghdr msg; | |
416 | struct iovec iov[4]; | |
417 | char fdbuf[CMSG_SPACE (sizeof (*fd))]; | |
418 | struct cmsghdr *cmsg; | |
419 | ssize_t size, fixed_size; | |
420 | int i; | |
421 | ||
422 | /* Build the message to receive data into. */ | |
423 | memset (&msg, 0, sizeof (msg)); | |
424 | msg.msg_iov = iov; | |
425 | ||
426 | iov[0].iov_base = type; | |
427 | iov[0].iov_len = sizeof (*type); | |
428 | iov[1].iov_base = int1; | |
429 | iov[1].iov_len = sizeof (*int1); | |
430 | iov[2].iov_base = int2; | |
431 | iov[2].iov_len = sizeof (*int2); | |
432 | iov[3].iov_base = buf; | |
433 | iov[3].iov_len = bufsiz; | |
434 | ||
435 | msg.msg_iovlen = 4; | |
436 | ||
437 | for (fixed_size = i = 0; i < msg.msg_iovlen - 1; i++) | |
438 | fixed_size += iov[i].iov_len; | |
439 | ||
440 | msg.msg_control = fdbuf; | |
441 | msg.msg_controllen = sizeof (fdbuf); | |
442 | ||
443 | /* Receive the message. */ | |
444 | size = recvmsg (sock, &msg, MSG_CMSG_CLOEXEC); | |
445 | if (size < 0) | |
446 | { | |
447 | if (debug_linux_namespaces) | |
6449ed0d GB |
448 | debug_printf ("namespace-helper: recv failed (%s)\n", |
449 | pulongest (size)); | |
4b8b5e72 GB |
450 | |
451 | mnsh_maybe_mourn_peer (); | |
452 | ||
453 | return size; | |
454 | } | |
455 | ||
456 | /* Check for truncation. */ | |
457 | if (size < fixed_size || (msg.msg_flags & (MSG_TRUNC | MSG_CTRUNC))) | |
458 | { | |
459 | if (debug_linux_namespaces) | |
6449ed0d GB |
460 | debug_printf ("namespace-helper: recv truncated (%s 0x%x)\n", |
461 | pulongest (size), msg.msg_flags); | |
4b8b5e72 GB |
462 | |
463 | mnsh_maybe_mourn_peer (); | |
464 | ||
465 | errno = EBADMSG; | |
466 | return -1; | |
467 | } | |
468 | ||
469 | /* Unpack the file descriptor if supplied. */ | |
470 | cmsg = CMSG_FIRSTHDR (&msg); | |
471 | if (cmsg != NULL | |
472 | && cmsg->cmsg_len == CMSG_LEN (sizeof (int)) | |
473 | && cmsg->cmsg_level == SOL_SOCKET | |
474 | && cmsg->cmsg_type == SCM_RIGHTS) | |
475 | memcpy (fd, CMSG_DATA (cmsg), sizeof (int)); | |
476 | else | |
477 | *fd = -1; | |
478 | ||
479 | if (debug_linux_namespaces) | |
480 | { | |
481 | debug_printf ("mnsh: recv: "); | |
482 | mnsh_debug_print_message (*type, *fd, *int1, *int2, buf, | |
483 | size - fixed_size); | |
484 | debug_printf ("\n"); | |
485 | } | |
486 | ||
487 | /* Return the number of bytes of data in BUF. */ | |
488 | return size - fixed_size; | |
489 | } | |
490 | ||
491 | /* Shortcuts for returning results from the helper. */ | |
492 | ||
493 | #define mnsh_return_int(sock, result, error) \ | |
494 | mnsh_send_message (sock, MNSH_RET_INT, -1, result, error, NULL, 0) | |
495 | ||
496 | #define mnsh_return_fd(sock, fd, error) \ | |
497 | mnsh_send_message (sock, MNSH_RET_FD, \ | |
498 | (fd) < 0 ? -1 : (fd), \ | |
499 | (fd) < 0 ? (fd) : 0, \ | |
500 | error, NULL, 0) | |
501 | ||
502 | #define mnsh_return_intstr(sock, result, buf, bufsiz, error) \ | |
503 | mnsh_send_message (sock, MNSH_RET_INTSTR, -1, result, error, \ | |
504 | buf, bufsiz) | |
505 | ||
506 | /* Handle a MNSH_REQ_SETNS message. Must be async-signal-safe. */ | |
507 | ||
508 | static ssize_t | |
509 | mnsh_handle_setns (int sock, int fd, int nstype) | |
510 | { | |
99fe86f7 | 511 | int result = do_setns (fd, nstype); |
4b8b5e72 GB |
512 | |
513 | return mnsh_return_int (sock, result, errno); | |
514 | } | |
515 | ||
516 | /* Handle a MNSH_REQ_OPEN message. Must be async-signal-safe. */ | |
517 | ||
518 | static ssize_t | |
519 | mnsh_handle_open (int sock, const char *filename, | |
520 | int flags, mode_t mode) | |
521 | { | |
522 | int fd = gdb_open_cloexec (filename, flags, mode); | |
523 | ssize_t result = mnsh_return_fd (sock, fd, errno); | |
524 | ||
525 | if (fd >= 0) | |
526 | close (fd); | |
527 | ||
528 | return result; | |
529 | } | |
530 | ||
531 | /* Handle a MNSH_REQ_UNLINK message. Must be async-signal-safe. */ | |
532 | ||
533 | static ssize_t | |
534 | mnsh_handle_unlink (int sock, const char *filename) | |
535 | { | |
536 | int result = unlink (filename); | |
537 | ||
538 | return mnsh_return_int (sock, result, errno); | |
539 | } | |
540 | ||
541 | /* Handle a MNSH_REQ_READLINK message. Must be async-signal-safe. */ | |
542 | ||
543 | static ssize_t | |
544 | mnsh_handle_readlink (int sock, const char *filename) | |
545 | { | |
546 | char buf[PATH_MAX]; | |
547 | int len = readlink (filename, buf, sizeof (buf)); | |
548 | ||
549 | return mnsh_return_intstr (sock, len, | |
550 | buf, len < 0 ? 0 : len, | |
551 | errno); | |
552 | } | |
553 | ||
554 | /* The helper process. Never returns. Must be async-signal-safe. */ | |
555 | ||
556 | static void mnsh_main (int sock) ATTRIBUTE_NORETURN; | |
557 | ||
558 | static void | |
559 | mnsh_main (int sock) | |
560 | { | |
561 | while (1) | |
562 | { | |
563 | enum mnsh_msg_type type; | |
564 | int fd, int1, int2; | |
565 | char buf[PATH_MAX]; | |
566 | ssize_t size, response = -1; | |
567 | ||
568 | size = mnsh_recv_message (sock, &type, | |
569 | &fd, &int1, &int2, | |
570 | buf, sizeof (buf)); | |
571 | ||
572 | if (size >= 0 && size < sizeof (buf)) | |
573 | { | |
574 | switch (type) | |
575 | { | |
576 | case MNSH_REQ_SETNS: | |
577 | if (fd > 0) | |
578 | response = mnsh_handle_setns (sock, fd, int1); | |
579 | break; | |
580 | ||
581 | case MNSH_REQ_OPEN: | |
582 | if (size > 0 && buf[size - 1] == '\0') | |
583 | response = mnsh_handle_open (sock, buf, int1, int2); | |
584 | break; | |
585 | ||
586 | case MNSH_REQ_UNLINK: | |
587 | if (size > 0 && buf[size - 1] == '\0') | |
588 | response = mnsh_handle_unlink (sock, buf); | |
589 | break; | |
590 | ||
591 | case MNSH_REQ_READLINK: | |
592 | if (size > 0 && buf[size - 1] == '\0') | |
593 | response = mnsh_handle_readlink (sock, buf); | |
594 | break; | |
595 | ||
596 | default: | |
597 | break; /* Handled below. */ | |
598 | } | |
599 | } | |
600 | ||
601 | /* Close any file descriptors we were passed. */ | |
602 | if (fd >= 0) | |
603 | close (fd); | |
604 | ||
605 | /* Can't handle this message, bounce it back. */ | |
606 | if (response < 0) | |
607 | { | |
608 | if (size < 0) | |
609 | size = 0; | |
610 | ||
611 | mnsh_send_message (sock, MNSH_MSG_ERROR, | |
612 | -1, int1, int2, buf, size); | |
613 | } | |
614 | } | |
615 | } | |
616 | ||
617 | /* The mount namespace helper process. */ | |
618 | ||
619 | struct linux_mnsh | |
620 | { | |
621 | /* PID of helper. */ | |
622 | pid_t pid; | |
623 | ||
624 | /* Socket for communication. */ | |
625 | int sock; | |
626 | ||
627 | /* ID of the mount namespace the helper is currently in. */ | |
628 | ino_t nsid; | |
629 | }; | |
630 | ||
631 | /* In the helper process this is set to the PID of the process that | |
632 | created the helper (i.e. GDB or gdbserver). In the main process | |
633 | this is set to zero. Used by mnsh_maybe_mourn_peer. */ | |
634 | static int mnsh_creator_pid = 0; | |
635 | ||
636 | /* Return an object representing the mount namespace helper process. | |
637 | If no mount namespace helper process has been started then start | |
638 | one. Return NULL if no mount namespace helper process could be | |
639 | started. */ | |
640 | ||
641 | static struct linux_mnsh * | |
642 | linux_mntns_get_helper (void) | |
643 | { | |
644 | static struct linux_mnsh *helper = NULL; | |
645 | ||
646 | if (helper == NULL) | |
647 | { | |
648 | static struct linux_mnsh h; | |
649 | struct linux_ns *ns; | |
650 | pid_t helper_creator = getpid (); | |
651 | int sv[2]; | |
652 | ||
653 | ns = linux_ns_get_namespace (LINUX_NS_MNT); | |
654 | if (ns == NULL) | |
655 | return NULL; | |
656 | ||
657 | if (gdb_socketpair_cloexec (AF_UNIX, SOCK_STREAM, 0, sv) < 0) | |
658 | return NULL; | |
659 | ||
eb0edac8 | 660 | h.pid = do_fork (); |
4b8b5e72 GB |
661 | if (h.pid < 0) |
662 | { | |
663 | int saved_errno = errno; | |
664 | ||
665 | close (sv[0]); | |
666 | close (sv[1]); | |
667 | ||
668 | errno = saved_errno; | |
669 | return NULL; | |
670 | } | |
671 | ||
672 | if (h.pid == 0) | |
673 | { | |
674 | /* Child process. */ | |
675 | close (sv[0]); | |
676 | ||
677 | mnsh_creator_pid = helper_creator; | |
678 | ||
679 | /* Debug printing isn't async-signal-safe. */ | |
680 | debug_linux_namespaces = 0; | |
681 | ||
682 | mnsh_main (sv[1]); | |
683 | } | |
684 | ||
685 | /* Parent process. */ | |
686 | close (sv[1]); | |
687 | ||
688 | helper = &h; | |
689 | helper->sock = sv[0]; | |
690 | helper->nsid = ns->id; | |
691 | ||
692 | if (debug_linux_namespaces) | |
693 | debug_printf ("Started mount namespace helper process %d\n", | |
694 | helper->pid); | |
695 | } | |
696 | ||
697 | return helper; | |
698 | } | |
699 | ||
700 | /* Check whether the other process died and act accordingly. Called | |
701 | whenever a socket error occurs, from both the main process and the | |
702 | helper. Must be async-signal-safe when called from the helper. */ | |
703 | ||
704 | static void | |
705 | mnsh_maybe_mourn_peer (void) | |
706 | { | |
707 | if (mnsh_creator_pid != 0) | |
708 | { | |
709 | /* We're in the helper. Check if our current parent is the | |
710 | process that started us. If it isn't, then our original | |
711 | parent died and we've been reparented. Exit immediately | |
712 | if that's the case. */ | |
713 | if (getppid () != mnsh_creator_pid) | |
714 | _exit (0); | |
715 | } | |
716 | else | |
717 | { | |
718 | /* We're in the main process. */ | |
719 | ||
720 | struct linux_mnsh *helper = linux_mntns_get_helper (); | |
721 | int status; | |
722 | pid_t pid; | |
723 | ||
724 | if (helper->pid < 0) | |
725 | { | |
726 | /* We already mourned it. */ | |
727 | return; | |
728 | } | |
729 | ||
730 | pid = waitpid (helper->pid, &status, WNOHANG); | |
731 | if (pid == 0) | |
732 | { | |
733 | /* The helper is still alive. */ | |
734 | return; | |
735 | } | |
736 | else if (pid == -1) | |
737 | { | |
738 | if (errno == ECHILD) | |
739 | warning (_("mount namespace helper vanished?")); | |
740 | else | |
741 | internal_warning (__FILE__, __LINE__, | |
742 | _("unhandled error %d"), errno); | |
743 | } | |
744 | else if (pid == helper->pid) | |
745 | { | |
746 | if (WIFEXITED (status)) | |
747 | warning (_("mount namespace helper exited with status %d"), | |
748 | WEXITSTATUS (status)); | |
749 | else if (WIFSIGNALED (status)) | |
750 | warning (_("mount namespace helper killed by signal %d"), | |
751 | WTERMSIG (status)); | |
752 | else | |
753 | internal_warning (__FILE__, __LINE__, | |
754 | _("unhandled status %d"), status); | |
755 | } | |
756 | else | |
757 | internal_warning (__FILE__, __LINE__, | |
758 | _("unknown pid %d"), pid); | |
759 | ||
760 | /* Something unrecoverable happened. */ | |
761 | helper->pid = -1; | |
762 | } | |
763 | } | |
764 | ||
765 | /* Shortcuts for sending messages to the helper. */ | |
766 | ||
767 | #define mnsh_send_setns(helper, fd, nstype) \ | |
768 | mnsh_send_message (helper->sock, MNSH_REQ_SETNS, fd, nstype, 0, \ | |
769 | NULL, 0) | |
770 | ||
771 | #define mnsh_send_open(helper, filename, flags, mode) \ | |
772 | mnsh_send_message (helper->sock, MNSH_REQ_OPEN, -1, flags, mode, \ | |
773 | filename, strlen (filename) + 1) | |
774 | ||
775 | #define mnsh_send_unlink(helper, filename) \ | |
776 | mnsh_send_message (helper->sock, MNSH_REQ_UNLINK, -1, 0, 0, \ | |
777 | filename, strlen (filename) + 1) | |
778 | ||
779 | #define mnsh_send_readlink(helper, filename) \ | |
780 | mnsh_send_message (helper->sock, MNSH_REQ_READLINK, -1, 0, 0, \ | |
781 | filename, strlen (filename) + 1) | |
782 | ||
783 | /* Receive a message from the helper. Issue an assertion failure if | |
784 | the message isn't a correctly-formatted MNSH_RET_INT. Set RESULT | |
785 | and ERROR and return 0 on success. Set errno and return -1 on | |
786 | failure. */ | |
787 | ||
788 | static int | |
789 | mnsh_recv_int (struct linux_mnsh *helper, int *result, int *error) | |
790 | { | |
791 | enum mnsh_msg_type type; | |
792 | char buf[PATH_MAX]; | |
793 | ssize_t size; | |
794 | int fd; | |
795 | ||
796 | size = mnsh_recv_message (helper->sock, &type, &fd, | |
797 | result, error, | |
798 | buf, sizeof (buf)); | |
799 | if (size < 0) | |
800 | return -1; | |
801 | ||
802 | gdb_assert (type == MNSH_RET_INT); | |
803 | gdb_assert (fd == -1); | |
804 | gdb_assert (size == 0); | |
805 | ||
806 | return 0; | |
807 | } | |
808 | ||
809 | /* Receive a message from the helper. Issue an assertion failure if | |
810 | the message isn't a correctly-formatted MNSH_RET_FD. Set FD and | |
811 | ERROR and return 0 on success. Set errno and return -1 on | |
812 | failure. */ | |
813 | ||
814 | static int | |
815 | mnsh_recv_fd (struct linux_mnsh *helper, int *fd, int *error) | |
816 | { | |
817 | enum mnsh_msg_type type; | |
818 | char buf[PATH_MAX]; | |
819 | ssize_t size; | |
820 | int result; | |
821 | ||
822 | size = mnsh_recv_message (helper->sock, &type, fd, | |
823 | &result, error, | |
824 | buf, sizeof (buf)); | |
825 | if (size < 0) | |
826 | return -1; | |
827 | ||
828 | gdb_assert (type == MNSH_RET_FD); | |
829 | gdb_assert (size == 0); | |
830 | ||
831 | if (*fd < 0) | |
832 | { | |
833 | gdb_assert (result < 0); | |
834 | *fd = result; | |
835 | } | |
836 | ||
837 | return 0; | |
838 | } | |
839 | ||
840 | /* Receive a message from the helper. Issue an assertion failure if | |
841 | the message isn't a correctly-formatted MNSH_RET_INTSTR. Set | |
842 | RESULT and ERROR and optionally store data in BUF, then return | |
843 | the number of bytes stored in BUF on success (this may be zero). | |
844 | Set errno and return -1 on error. */ | |
845 | ||
846 | static ssize_t | |
847 | mnsh_recv_intstr (struct linux_mnsh *helper, | |
848 | int *result, int *error, | |
849 | void *buf, int bufsiz) | |
850 | { | |
851 | enum mnsh_msg_type type; | |
852 | ssize_t size; | |
853 | int fd; | |
854 | ||
855 | size = mnsh_recv_message (helper->sock, &type, &fd, | |
856 | result, error, | |
857 | buf, bufsiz); | |
858 | ||
859 | if (size < 0) | |
860 | return -1; | |
861 | ||
862 | gdb_assert (type == MNSH_RET_INTSTR); | |
863 | gdb_assert (fd == -1); | |
864 | ||
865 | return size; | |
866 | } | |
867 | ||
868 | /* Return values for linux_mntns_access_fs. */ | |
869 | ||
870 | enum mnsh_fs_code | |
871 | { | |
872 | /* Something went wrong, errno is set. */ | |
873 | MNSH_FS_ERROR = -1, | |
874 | ||
875 | /* The main process is in the correct mount namespace. | |
876 | The caller should access the filesystem directly. */ | |
877 | MNSH_FS_DIRECT, | |
878 | ||
879 | /* The helper is in the correct mount namespace. | |
880 | The caller should access the filesystem via the helper. */ | |
881 | MNSH_FS_HELPER | |
882 | }; | |
883 | ||
884 | /* Return a value indicating how the caller should access the | |
885 | mount namespace of process PID. */ | |
886 | ||
887 | static enum mnsh_fs_code | |
888 | linux_mntns_access_fs (pid_t pid) | |
889 | { | |
890 | struct cleanup *old_chain; | |
891 | struct linux_ns *ns; | |
892 | struct stat sb; | |
893 | struct linux_mnsh *helper; | |
894 | ssize_t size; | |
895 | int fd, saved_errno; | |
896 | ||
897 | if (pid == getpid ()) | |
898 | return MNSH_FS_DIRECT; | |
899 | ||
900 | ns = linux_ns_get_namespace (LINUX_NS_MNT); | |
901 | if (ns == NULL) | |
902 | return MNSH_FS_DIRECT; | |
903 | ||
904 | old_chain = make_cleanup (null_cleanup, NULL); | |
905 | ||
906 | fd = gdb_open_cloexec (linux_ns_filename (ns, pid), O_RDONLY, 0); | |
907 | if (fd < 0) | |
908 | goto error; | |
909 | ||
f36b8719 | 910 | make_cleanup_close (fd); |
4b8b5e72 GB |
911 | |
912 | if (fstat (fd, &sb) != 0) | |
913 | goto error; | |
914 | ||
915 | if (sb.st_ino == ns->id) | |
916 | { | |
917 | do_cleanups (old_chain); | |
918 | ||
919 | return MNSH_FS_DIRECT; | |
920 | } | |
921 | ||
922 | helper = linux_mntns_get_helper (); | |
923 | if (helper == NULL) | |
924 | goto error; | |
925 | ||
926 | if (sb.st_ino != helper->nsid) | |
927 | { | |
928 | int result, error; | |
929 | ||
930 | size = mnsh_send_setns (helper, fd, 0); | |
931 | if (size < 0) | |
932 | goto error; | |
933 | ||
934 | if (mnsh_recv_int (helper, &result, &error) != 0) | |
935 | goto error; | |
936 | ||
937 | if (result != 0) | |
938 | { | |
939 | /* ENOSYS indicates that an entire function is unsupported | |
940 | (it's not appropriate for our versions of open/unlink/ | |
941 | readlink to sometimes return with ENOSYS depending on how | |
942 | they're called) so we convert ENOSYS to ENOTSUP if setns | |
943 | fails. */ | |
944 | if (error == ENOSYS) | |
945 | error = ENOTSUP; | |
946 | ||
947 | errno = error; | |
948 | goto error; | |
949 | } | |
950 | ||
951 | helper->nsid = sb.st_ino; | |
952 | } | |
953 | ||
954 | do_cleanups (old_chain); | |
955 | ||
956 | return MNSH_FS_HELPER; | |
957 | ||
958 | error: | |
959 | saved_errno = errno; | |
960 | ||
961 | do_cleanups (old_chain); | |
962 | ||
963 | errno = saved_errno; | |
964 | return MNSH_FS_ERROR; | |
965 | } | |
966 | ||
967 | /* See nat/linux-namespaces.h. */ | |
968 | ||
969 | int | |
970 | linux_mntns_open_cloexec (pid_t pid, const char *filename, | |
971 | int flags, mode_t mode) | |
972 | { | |
973 | enum mnsh_fs_code access = linux_mntns_access_fs (pid); | |
974 | struct linux_mnsh *helper; | |
975 | int fd, error; | |
976 | ssize_t size; | |
977 | ||
978 | if (access == MNSH_FS_ERROR) | |
979 | return -1; | |
980 | ||
981 | if (access == MNSH_FS_DIRECT) | |
982 | return gdb_open_cloexec (filename, flags, mode); | |
983 | ||
984 | gdb_assert (access == MNSH_FS_HELPER); | |
985 | ||
986 | helper = linux_mntns_get_helper (); | |
987 | ||
988 | size = mnsh_send_open (helper, filename, flags, mode); | |
989 | if (size < 0) | |
990 | return -1; | |
991 | ||
992 | if (mnsh_recv_fd (helper, &fd, &error) != 0) | |
993 | return -1; | |
994 | ||
995 | if (fd < 0) | |
996 | errno = error; | |
997 | ||
998 | return fd; | |
999 | } | |
1000 | ||
1001 | /* See nat/linux-namespaces.h. */ | |
1002 | ||
1003 | int | |
1004 | linux_mntns_unlink (pid_t pid, const char *filename) | |
1005 | { | |
1006 | enum mnsh_fs_code access = linux_mntns_access_fs (pid); | |
1007 | struct linux_mnsh *helper; | |
1008 | int ret, error; | |
1009 | ssize_t size; | |
1010 | ||
1011 | if (access == MNSH_FS_ERROR) | |
1012 | return -1; | |
1013 | ||
1014 | if (access == MNSH_FS_DIRECT) | |
1015 | return unlink (filename); | |
1016 | ||
1017 | gdb_assert (access == MNSH_FS_HELPER); | |
1018 | ||
1019 | helper = linux_mntns_get_helper (); | |
1020 | ||
1021 | size = mnsh_send_unlink (helper, filename); | |
1022 | if (size < 0) | |
1023 | return -1; | |
1024 | ||
1025 | if (mnsh_recv_int (helper, &ret, &error) != 0) | |
1026 | return -1; | |
1027 | ||
1028 | if (ret != 0) | |
1029 | errno = error; | |
1030 | ||
1031 | return ret; | |
1032 | } | |
1033 | ||
1034 | /* See nat/linux-namespaces.h. */ | |
1035 | ||
1036 | ssize_t | |
1037 | linux_mntns_readlink (pid_t pid, const char *filename, | |
1038 | char *buf, size_t bufsiz) | |
1039 | { | |
1040 | enum mnsh_fs_code access = linux_mntns_access_fs (pid); | |
1041 | struct linux_mnsh *helper; | |
1042 | int ret, error; | |
1043 | ssize_t size; | |
1044 | ||
1045 | if (access == MNSH_FS_ERROR) | |
1046 | return -1; | |
1047 | ||
1048 | if (access == MNSH_FS_DIRECT) | |
1049 | return readlink (filename, buf, bufsiz); | |
1050 | ||
1051 | gdb_assert (access == MNSH_FS_HELPER); | |
1052 | ||
1053 | helper = linux_mntns_get_helper (); | |
1054 | ||
1055 | size = mnsh_send_readlink (helper, filename); | |
1056 | if (size < 0) | |
1057 | return -1; | |
1058 | ||
1059 | size = mnsh_recv_intstr (helper, &ret, &error, buf, bufsiz); | |
1060 | ||
1061 | if (size < 0) | |
1062 | { | |
1063 | ret = -1; | |
1064 | errno = error; | |
1065 | } | |
1066 | else | |
1067 | gdb_assert (size == ret); | |
1068 | ||
1069 | return ret; | |
1070 | } |