1 /*
2 * Copyright (c) 2005, 2018, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "logging/log.hpp"
27 #include "memory/allocation.inline.hpp"
28 #include "runtime/interfaceSupport.inline.hpp"
29 #include "runtime/os.inline.hpp"
30 #include "services/attachListener.hpp"
31 #include "services/dtraceAttacher.hpp"
32
33 #include <unistd.h>
34 #include <signal.h>
35 #include <sys/types.h>
36 #include <sys/socket.h>
37 #include <sys/un.h>
38 #include <sys/stat.h>
39
40 #ifndef UNIX_PATH_MAX
41 #define UNIX_PATH_MAX sizeof(((struct sockaddr_un *)0)->sun_path)
42 #endif
43
44 // The attach mechanism on Linux uses a UNIX domain socket. An attach listener
45 // thread is created at startup or is created on-demand via a signal from
46 // the client tool. The attach listener creates a socket and binds it to a file
47 // in the filesystem. The attach listener then acts as a simple (single-
48 // threaded) server - it waits for a client to connect, reads the request,
49 // executes it, and returns the response to the client via the socket
50 // connection.
51 //
52 // As the socket is a UNIX domain socket it means that only clients on the
53 // local machine can connect. In addition there are two other aspects to
54 // the security:
55 // 1. The well known file that the socket is bound to has permission 400
56 // 2. When a client connect, the SO_PEERCRED socket option is used to
57 // obtain the credentials of client. We check that the effective uid
58 // of the client matches this process.
59
60 // forward reference
61 class LinuxAttachOperation;
62
63 class LinuxAttachListener: AllStatic {
64 private:
65 // the path to which we bind the UNIX domain socket
66 static char _path[UNIX_PATH_MAX];
67 static bool _has_path;
68
69 // the file descriptor for the listening socket
70 static int _listener;
71
72 static void set_path(char* path) {
73 if (path == NULL) {
74 _has_path = false;
75 } else {
76 strncpy(_path, path, UNIX_PATH_MAX);
77 _path[UNIX_PATH_MAX-1] = '\0';
78 _has_path = true;
79 }
80 }
81
82 static void set_listener(int s) { _listener = s; }
83
84 // reads a request from the given connected socket
85 static LinuxAttachOperation* read_request(int s);
86
87 public:
88 enum {
89 ATTACH_PROTOCOL_VER = 1 // protocol version
90 };
91 enum {
92 ATTACH_ERROR_BADVERSION = 101 // error codes
93 };
94
95 // initialize the listener, returns 0 if okay
96 static int init();
97
98 static char* path() { return _path; }
99 static bool has_path() { return _has_path; }
100 static int listener() { return _listener; }
101
102 // write the given buffer to a socket
103 static int write_fully(int s, char* buf, int len);
104
105 static LinuxAttachOperation* dequeue();
106 };
107
108 class LinuxAttachOperation: public AttachOperation {
109 private:
110 // the connection to the client
111 int _socket;
112
113 public:
114 void complete(jint res, bufferedStream* st);
115
116 void set_socket(int s) { _socket = s; }
117 int socket() const { return _socket; }
118
119 LinuxAttachOperation(char* name) : AttachOperation(name) {
120 set_socket(-1);
121 }
122 };
123
124 // statics
125 char LinuxAttachListener::_path[UNIX_PATH_MAX];
126 bool LinuxAttachListener::_has_path;
127 int LinuxAttachListener::_listener = -1;
128
129 // Supporting class to help split a buffer into individual components
130 class ArgumentIterator : public StackObj {
131 private:
132 char* _pos;
133 char* _end;
134 public:
135 ArgumentIterator(char* arg_buffer, size_t arg_size) {
136 _pos = arg_buffer;
137 _end = _pos + arg_size - 1;
138 }
139 char* next() {
140 if (*_pos == '\0') {
141 // advance the iterator if possible (null arguments)
142 if (_pos < _end) {
143 _pos += 1;
144 }
145 return NULL;
146 }
147 char* res = _pos;
148 char* next_pos = strchr(_pos, '\0');
149 if (next_pos < _end) {
150 next_pos++;
151 }
152 _pos = next_pos;
153 return res;
154 }
155 };
156
157
158 // atexit hook to stop listener and unlink the file that it is
159 // bound too.
160 extern "C" {
161 static void listener_cleanup() {
162 static int cleanup_done;
163 if (!cleanup_done) {
164 cleanup_done = 1;
165 int s = LinuxAttachListener::listener();
166 if (s != -1) {
167 ::close(s);
168 }
169 if (LinuxAttachListener::has_path()) {
170 ::unlink(LinuxAttachListener::path());
171 }
172 }
173 }
174 }
175
176 // Initialization - create a listener socket and bind it to a file
177
178 int LinuxAttachListener::init() {
179 char path[UNIX_PATH_MAX]; // socket file
180 char initial_path[UNIX_PATH_MAX]; // socket file during setup
181 int listener; // listener socket (file descriptor)
182
183 // register function to cleanup
184 ::atexit(listener_cleanup);
185
186 int n = snprintf(path, UNIX_PATH_MAX, "%s/.java_pid%d",
187 os::get_temp_directory(), os::current_process_id());
188 if (n < (int)UNIX_PATH_MAX) {
189 n = snprintf(initial_path, UNIX_PATH_MAX, "%s.tmp", path);
190 }
191 if (n >= (int)UNIX_PATH_MAX) {
192 return -1;
193 }
194
195 // create the listener socket
196 listener = ::socket(PF_UNIX, SOCK_STREAM, 0);
197 if (listener == -1) {
198 return -1;
199 }
200
201 // bind socket
202 struct sockaddr_un addr;
203 memset((void *)&addr, 0, sizeof(addr));
204 addr.sun_family = AF_UNIX;
205 strcpy(addr.sun_path, initial_path);
206 ::unlink(initial_path);
207 int res = ::bind(listener, (struct sockaddr*)&addr, sizeof(addr));
208 if (res == -1) {
209 ::close(listener);
210 return -1;
211 }
212
213 // put in listen mode, set permissions, and rename into place
214 res = ::listen(listener, 5);
215 if (res == 0) {
216 RESTARTABLE(::chmod(initial_path, S_IREAD|S_IWRITE), res);
217 if (res == 0) {
218 // make sure the file is owned by the effective user and effective group
219 // e.g. the group could be inherited from the directory in case the s bit is set
220 RESTARTABLE(::chown(initial_path, geteuid(), getegid()), res);
221 if (res == 0) {
222 res = ::rename(initial_path, path);
223 }
224 }
225 }
226 if (res == -1) {
227 ::close(listener);
228 ::unlink(initial_path);
229 return -1;
230 }
231 set_path(path);
232 set_listener(listener);
233
234 return 0;
235 }
236
237 // Given a socket that is connected to a peer we read the request and
238 // create an AttachOperation. As the socket is blocking there is potential
239 // for a denial-of-service if the peer does not response. However this happens
240 // after the peer credentials have been checked and in the worst case it just
241 // means that the attach listener thread is blocked.
242 //
243 LinuxAttachOperation* LinuxAttachListener::read_request(int s) {
244 char ver_str[8];
245 sprintf(ver_str, "%d", ATTACH_PROTOCOL_VER);
246
247 // The request is a sequence of strings so we first figure out the
248 // expected count and the maximum possible length of the request.
249 // The request is:
250 // <ver>0<cmd>0<arg>0<arg>0<arg>0
251 // where <ver> is the protocol version (1), <cmd> is the command
252 // name ("load", "datadump", ...), and <arg> is an argument
253 int expected_str_count = 2 + AttachOperation::arg_count_max;
254 const int max_len = (sizeof(ver_str) + 1) + (AttachOperation::name_length_max + 1) +
255 AttachOperation::arg_count_max*(AttachOperation::arg_length_max + 1);
256
257 char buf[max_len];
258 int str_count = 0;
259
260 // Read until all (expected) strings have been read, the buffer is
261 // full, or EOF.
262
263 int off = 0;
264 int left = max_len;
265
266 do {
267 int n;
268 RESTARTABLE(read(s, buf+off, left), n);
269 assert(n <= left, "buffer was too small, impossible!");
270 buf[max_len - 1] = '\0';
271 if (n == -1) {
272 return NULL; // reset by peer or other error
273 }
274 if (n == 0) {
275 break;
276 }
277 for (int i=0; i<n; i++) {
278 if (buf[off+i] == 0) {
279 // EOS found
280 str_count++;
281
282 // The first string is <ver> so check it now to
283 // check for protocol mis-match
284 if (str_count == 1) {
285 if ((strlen(buf) != strlen(ver_str)) ||
286 (atoi(buf) != ATTACH_PROTOCOL_VER)) {
287 char msg[32];
288 sprintf(msg, "%d\n", ATTACH_ERROR_BADVERSION);
289 write_fully(s, msg, strlen(msg));
290 return NULL;
291 }
292 }
293 }
294 }
295 off += n;
296 left -= n;
297 } while (left > 0 && str_count < expected_str_count);
298
299 if (str_count != expected_str_count) {
300 return NULL; // incomplete request
301 }
302
303 // parse request
304
305 ArgumentIterator args(buf, (max_len)-left);
306
307 // version already checked
308 char* v = args.next();
309
310 char* name = args.next();
311 if (name == NULL || strlen(name) > AttachOperation::name_length_max) {
312 return NULL;
313 }
314
315 LinuxAttachOperation* op = new LinuxAttachOperation(name);
316
317 for (int i=0; i<AttachOperation::arg_count_max; i++) {
318 char* arg = args.next();
319 if (arg == NULL) {
320 op->set_arg(i, NULL);
321 } else {
322 if (strlen(arg) > AttachOperation::arg_length_max) {
323 delete op;
324 return NULL;
325 }
326 op->set_arg(i, arg);
327 }
328 }
329
330 op->set_socket(s);
331 return op;
332 }
333
334
335 // Dequeue an operation
336 //
337 // In the Linux implementation there is only a single operation and clients
338 // cannot queue commands (except at the socket level).
339 //
340 LinuxAttachOperation* LinuxAttachListener::dequeue() {
341 for (;;) {
342 int s;
343
344 // wait for client to connect
345 struct sockaddr addr;
346 socklen_t len = sizeof(addr);
347 RESTARTABLE(::accept(listener(), &addr, &len), s);
348 if (s == -1) {
349 return NULL; // log a warning?
350 }
351
352 // get the credentials of the peer and check the effective uid/guid
353 struct ucred cred_info;
354 socklen_t optlen = sizeof(cred_info);
355 if (::getsockopt(s, SOL_SOCKET, SO_PEERCRED, (void*)&cred_info, &optlen) == -1) {
356 log_debug(attach)("Failed to get socket option SO_PEERCRED");
357 ::close(s);
358 continue;
359 }
360
361 if (!os::Posix::matches_effective_uid_and_gid_or_root(cred_info.uid, cred_info.gid)) {
362 log_debug(attach)("euid/egid check failed (%d/%d vs %d/%d)",
363 cred_info.uid, cred_info.gid, geteuid(), getegid());
364 ::close(s);
365 continue;
366 }
367
368 // peer credential look okay so we read the request
369 LinuxAttachOperation* op = read_request(s);
370 if (op == NULL) {
371 ::close(s);
372 continue;
373 } else {
374 return op;
375 }
376 }
377 }
378
379 // write the given buffer to the socket
380 int LinuxAttachListener::write_fully(int s, char* buf, int len) {
381 do {
382 int n = ::write(s, buf, len);
383 if (n == -1) {
384 if (errno != EINTR) return -1;
385 } else {
386 buf += n;
387 len -= n;
388 }
389 }
390 while (len > 0);
391 return 0;
392 }
393
394 // Complete an operation by sending the operation result and any result
395 // output to the client. At this time the socket is in blocking mode so
396 // potentially we can block if there is a lot of data and the client is
397 // non-responsive. For most operations this is a non-issue because the
398 // default send buffer is sufficient to buffer everything. In the future
399 // if there are operations that involves a very big reply then it the
400 // socket could be made non-blocking and a timeout could be used.
401
402 void LinuxAttachOperation::complete(jint result, bufferedStream* st) {
403 JavaThread* thread = JavaThread::current();
404 ThreadBlockInVM tbivm(thread);
405
406 thread->set_suspend_equivalent();
407 // cleared by handle_special_suspend_equivalent_condition() or
408 // java_suspend_self() via check_and_wait_while_suspended()
409
410 // write operation result
411 char msg[32];
412 sprintf(msg, "%d\n", result);
413 int rc = LinuxAttachListener::write_fully(this->socket(), msg, strlen(msg));
414
415 // write any result data
416 if (rc == 0) {
417 LinuxAttachListener::write_fully(this->socket(), (char*) st->base(), st->size());
418 ::shutdown(this->socket(), 2);
419 }
420
421 // done
422 ::close(this->socket());
423
424 // were we externally suspended while we were waiting?
425 thread->check_and_wait_while_suspended();
426
427 delete this;
428 }
429
430
431 // AttachListener functions
432
433 AttachOperation* AttachListener::dequeue() {
434 JavaThread* thread = JavaThread::current();
435 ThreadBlockInVM tbivm(thread);
436
437 thread->set_suspend_equivalent();
438 // cleared by handle_special_suspend_equivalent_condition() or
439 // java_suspend_self() via check_and_wait_while_suspended()
440
441 AttachOperation* op = LinuxAttachListener::dequeue();
442
443 // were we externally suspended while we were waiting?
444 thread->check_and_wait_while_suspended();
445
446 return op;
447 }
448
449 // Performs initialization at vm startup
450 // For Linux we remove any stale .java_pid file which could cause
451 // an attaching process to think we are ready to receive on the
452 // domain socket before we are properly initialized
453
454 void AttachListener::vm_start() {
455 char fn[UNIX_PATH_MAX];
456 struct stat64 st;
457 int ret;
458
459 int n = snprintf(fn, UNIX_PATH_MAX, "%s/.java_pid%d",
460 os::get_temp_directory(), os::current_process_id());
461 assert(n < (int)UNIX_PATH_MAX, "java_pid file name buffer overflow");
462
463 RESTARTABLE(::stat64(fn, &st), ret);
464 if (ret == 0) {
465 ret = ::unlink(fn);
466 if (ret == -1) {
467 log_debug(attach)("Failed to remove stale attach pid file at %s", fn);
468 }
469 }
470 }
471
472 int AttachListener::pd_init() {
473 JavaThread* thread = JavaThread::current();
474 ThreadBlockInVM tbivm(thread);
475
476 thread->set_suspend_equivalent();
477 // cleared by handle_special_suspend_equivalent_condition() or
478 // java_suspend_self() via check_and_wait_while_suspended()
479
480 int ret_code = LinuxAttachListener::init();
481
482 // were we externally suspended while we were waiting?
483 thread->check_and_wait_while_suspended();
484
485 return ret_code;
486 }
487
488 // Attach Listener is started lazily except in the case when
489 // +ReduseSignalUsage is used
490 bool AttachListener::init_at_startup() {
491 if (ReduceSignalUsage) {
492 return true;
493 } else {
494 return false;
495 }
496 }
497
498 // If the file .attach_pid<pid> exists in the working directory
499 // or /tmp then this is the trigger to start the attach mechanism
500 bool AttachListener::is_init_trigger() {
501 if (init_at_startup() || is_initialized()) {
502 return false; // initialized at startup or already initialized
503 }
504 char fn[PATH_MAX + 1];
505 int ret;
506 struct stat64 st;
507 sprintf(fn, ".attach_pid%d", os::current_process_id());
508 RESTARTABLE(::stat64(fn, &st), ret);
509 if (ret == -1) {
510 log_trace(attach)("Failed to find attach file: %s, trying alternate", fn);
511 snprintf(fn, sizeof(fn), "%s/.attach_pid%d",
512 os::get_temp_directory(), os::current_process_id());
513 RESTARTABLE(::stat64(fn, &st), ret);
514 if (ret == -1) {
515 log_debug(attach)("Failed to find attach file: %s", fn);
516 }
517 }
518 if (ret == 0) {
519 // simple check to avoid starting the attach mechanism when
520 // a bogus non-root user creates the file
521 if (os::Posix::matches_effective_uid_or_root(st.st_uid)) {
522 init();
523 log_trace(attach)("Attach triggered by %s", fn);
524 return true;
525 } else {
526 log_debug(attach)("File %s has wrong user id %d (vs %d). Attach is not triggered", fn, st.st_uid, geteuid());
527 }
528 }
529 return false;
530 }
531
532 // if VM aborts then remove listener
533 void AttachListener::abort() {
534 listener_cleanup();
535 }
536
537 void AttachListener::pd_data_dump() {
538 os::signal_notify(SIGQUIT);
539 }
540
541 AttachOperationFunctionInfo* AttachListener::pd_find_operation(const char* n) {
542 return NULL;
543 }
544
545 jint AttachListener::pd_set_flag(AttachOperation* op, outputStream* out) {
546 out->print_cr("flag '%s' cannot be changed", op->arg(0));
547 return JNI_ERR;
548 }
549
550 void AttachListener::pd_detachall() {
551 // do nothing for now
552 }