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