mono/metadata/attach.c

   1 /*
   2  * attach.c: Support for attaching to the runtime from other processes.
   3  *
   4  * Author:
   5  *   Zoltan Varga (vargaz@gmail.com)
   6  *
   7  * Copyright 2007-2009 Novell, Inc (http://www.novell.com)
   8  */
   9
  10 #include <config.h>
  11 #include <glib.h>
  12
  13 #ifdef HOST_WIN32
  14 #define DISABLE_ATTACH
  15 #endif
  16 #ifndef DISABLE_ATTACH
  17
  18 #include <stdio.h>
  19 #include <stdlib.h>
  20 #include <string.h>
  21 #include <sys/types.h>
  22 #include <sys/socket.h>
  23 #include <sys/stat.h>
  24 #include <sys/un.h>
  25 #include <netinet/in.h>
  26 #include <sys/types.h>
  27 #include <sys/stat.h>
  28 #include <fcntl.h>
  29 #include <pwd.h>
  30 #include <errno.h>
  31 #include <netdb.h>
  32 #include <unistd.h>
  33
  34
  35 #include <mono/metadata/assembly.h>
  36 #include <mono/metadata/metadata.h>
  37 #include <mono/metadata/class-internals.h>
  38 #include <mono/metadata/object-internals.h>
  39 #include <mono/metadata/threads-types.h>
  40 #include <mono/metadata/gc-internal.h>
  41 #include "attach.h"
  42
  43 /*
  44  * This module enables other processes to attach to a running mono process and
  45  * load agent assemblies.
  46  * Communication is done through a UNIX Domain Socket located at
  47  * /tmp/mono-<USER>/.mono-<PID>.
  48  * We use a simplified version of the .net remoting protocol.
  49  * To increase security, and to avoid spinning up a listener thread on startup,
  50  * we follow the java implementation, and only start up the attach mechanism
  51  * when we receive a QUIT signal and there is a file named
  52  * '.mono_attach_pid<PID>' in /tmp.
  53  *
  54  * SECURITY:
  55  * - This module allows loading of arbitrary code into a running mono runtime, so
  56  *   it is security critical.
  57  * - Security is based on controlling access to the unix file to which the unix
  58  *   domain socket is bound. Permissions/ownership are set such that only the owner
  59  *   of the process can access the socket.
  60  * - As an additional measure, the socket is only created when the process receives
  61  *   a SIGQUIT signal, which only its owner/root can send.
  62  * - The socket is kept in a directory whose ownership is checked before creating
  63  *   the socket. This could allow an attacker a kind of DOS attack by creating the
  64  *   directory with the wrong permissions/ownership. However, the only thing such
  65  *   an attacker could prevent is the attaching of agents to the mono runtime.
  66  */
  67
  68 typedef struct {
  69         gboolean enabled;
  70 } AgentConfig;
  71
  72 typedef struct {
  73         int bytes_sent;
  74 } AgentStats;
  75
  76 /*******************************************************************/
  77 /* Remoting Protocol type definitions from [MS-NRBF] and [MS-NRTP] */
  78 /*******************************************************************/
  79
  80 typedef enum {
  81         PRIM_TYPE_INT32 = 8,
  82         PRIM_TYPE_INT64 = 9,
  83         PRIM_TYPE_NULL = 17,
  84         PRIM_TYPE_STRING = 18
  85 } PrimitiveType;
  86
  87 static AgentConfig config;
  88
  89 static int listen_fd, conn_fd;
  90
  91 static char *ipc_filename;
  92
  93 static char *server_uri;
  94
  95 static HANDLE receiver_thread_handle;
  96
  97 static gboolean stop_receiver_thread;
  98
  99 static gboolean needs_to_start, started;
 100
 101 #define agent_lock() EnterCriticalSection (&agent_mutex)
 102 #define agent_unlock() LeaveCriticalSection (&agent_mutex)
 103 static CRITICAL_SECTION agent_mutex;
 104
 105 static void transport_connect (void);
 106
 107 static guint32 WINAPI receiver_thread (void *arg);
 108
 109 static void transport_start_receive (void);
 110
 111 /*
 112  * Functions to decode protocol data
 113  */
 114 static inline int
 115 decode_byte (guint8 *buf, guint8 **endbuf, guint8 *limit)
 116 {
 117         *endbuf = buf + 1;
 118         g_assert (*endbuf <= limit);
 119         return buf [0];
 120 }
 121
 122 static inline int
 123 decode_int (guint8 *buf, guint8 **endbuf, guint8 *limit)
 124 {
 125         *endbuf = buf + 4;
 126         g_assert (*endbuf <= limit);
 127
 128         return (((int)buf [0]) << 0) | (((int)buf [1]) << 8) | (((int)buf [2]) << 16) | (((int)buf [3]) << 24);
 129 }
 130
 131 static inline int
 132 decode_short (guint8 *buf, guint8 **endbuf, guint8 *limit)
 133 {
 134         *endbuf = buf + 2;
 135         g_assert (*endbuf <= limit);
 136
 137         return (((int)buf [0]) << 0) | (((int)buf [1]) << 8);
 138 }
 139
 140 static char*
 141 decode_string_value (guint8 *buf, guint8 **endbuf, guint8 *limit)
 142 {
 143         int type;
 144     gint32 length;
 145         guint8 *p = buf;
 146         char *s;
 147
 148         type = decode_byte (p, &p, limit);
 149         if (type == PRIM_TYPE_NULL) {
 150                 *endbuf = p;
 151                 return NULL;
 152         }
 153         g_assert (type == PRIM_TYPE_STRING);
 154
 155         length = 0;
 156         while (TRUE) {
 157                 guint8 b = decode_byte (p, &p, limit);
 158
 159                 length <<= 8;
 160                 length += b;
 161                 if (b <= 0x7f)
 162                         break;
 163         }
 164
 165         g_assert (length < (1 << 16));
 166
 167         s = g_malloc (length + 1);
 168
 169         g_assert (p + length <= limit);
 170         memcpy (s, p, length);
 171         s [length] = '\0';
 172         p += length;
 173
 174         *endbuf = p;
 175
 176         return s;
 177 }
 178
 179 /********************************/
 180 /*    AGENT IMPLEMENTATION      */
 181 /********************************/
 182
 183 void
 184 mono_attach_parse_options (char *options)
 185 {
 186         if (!options)
 187                 return;
 188         if (!strcmp (options, "disable"))
 189                 config.enabled = FALSE;
 190 }
 191
 192 void
 193 mono_attach_init (void)
 194 {
 195         InitializeCriticalSection (&agent_mutex);
 196
 197         config.enabled = TRUE;
 198 }
 199
 200 /**
 201  * mono_attach_start:
 202  *
 203  * Start the attach mechanism if needed.  This is called from a signal handler so it must be signal safe.
 204  *
 205  * Returns: whenever it was started.
 206  */
 207 gboolean
 208 mono_attach_start (void)
 209 {
 210         char path [256];
 211         int fd;
 212
 213         if (started)
 214                 return FALSE;
 215
 216         /* Check for the existence of the trigger file */
 217
 218         /*
 219          * We don't do anything with this file, and the only thing an attacker can do
 220          * by creating it is to enable the attach mechanism if the process receives a
 221          * SIGQUIT signal, which can only be sent by the owner/root.
 222          */
 223         snprintf (path, sizeof (path), "/tmp/.mono_attach_pid%d", getpid ());
 224         fd = open (path, O_RDONLY);
 225         if (fd == -1)
 226                 return FALSE;
 227         close (fd);
 228
 229         if (!config.enabled)
 230                 /* Act like we started */
 231                 return TRUE;
 232
 233         if (started)
 234                 return FALSE;
 235
 236         /*
 237          * Our startup includes non signal-safe code, so ask the finalizer thread to
 238          * do the actual startup.
 239          */
 240         needs_to_start = TRUE;
 241         mono_gc_finalize_notify ();
 242
 243         return TRUE;
 244 }
 245
 246 /* Called by the finalizer thread when it is woken up */
 247 void
 248 mono_attach_maybe_start (void)
 249 {
 250         if (!needs_to_start)
 251                 return;
 252
 253         needs_to_start = FALSE;
 254         if (!started) {
 255                 transport_start_receive ();
 256
 257                 started = TRUE;
 258         }
 259 }
 260
 261 void
 262 mono_attach_cleanup (void)
 263 {
 264         if (listen_fd)
 265                 close (listen_fd);
 266         if (ipc_filename)
 267                 unlink (ipc_filename);
 268
 269         stop_receiver_thread = TRUE;
 270         if (conn_fd)
 271                 /* This will cause receiver_thread () to break out of the read () call */
 272                 close (conn_fd);
 273
 274         /* Wait for the receiver thread to exit */
 275         if (receiver_thread_handle)
 276                 WaitForSingleObjectEx (receiver_thread_handle, 0, FALSE);
 277 }
 278
 279 static int
 280 mono_attach_load_agent (MonoDomain *domain, char *agent, char *args, MonoObject **exc)
 281 {
 282         MonoAssembly *agent_assembly;
 283         MonoImage *image;
 284         MonoMethod *method;
 285         guint32 entry;
 286         MonoArray *main_args;
 287         gpointer pa [1];
 288         MonoImageOpenStatus open_status;
 289
 290         agent_assembly = mono_assembly_open (agent, &open_status);
 291         if (!agent_assembly) {
 292                 fprintf (stderr, "Cannot open agent assembly '%s': %s.\n", agent, mono_image_strerror (open_status));
 293                 g_free (agent);
 294                 return 2;
 295         }
 296
 297         /*
 298          * Can't use mono_jit_exec (), as it sets things which might confuse the
 299          * real Main method.
 300          */
 301         image = mono_assembly_get_image (agent_assembly);
 302         entry = mono_image_get_entry_point (image);
 303         if (!entry) {
 304                 g_print ("Assembly '%s' doesn't have an entry point.\n", mono_image_get_filename (image));
 305                 g_free (agent);
 306                 return 1;
 307         }
 308
 309         method = mono_get_method (image, entry, NULL);
 310         if (method == NULL){
 311                 g_print ("The entry point method of assembly '%s' could not be loaded\n", agent);
 312                 g_free (agent);
 313                 return 1;
 314         }
 315
 316         if (args) {
 317                 main_args = (MonoArray*)mono_array_new (domain, mono_defaults.string_class, 1);
 318                 mono_array_set (main_args, MonoString*, 0, mono_string_new (domain, args));
 319         } else {
 320                 main_args = (MonoArray*)mono_array_new (domain, mono_defaults.string_class, 0);
 321         }
 322
 323         g_free (agent);
 324
 325         pa [0] = main_args;
 326         mono_runtime_invoke (method, NULL, pa, exc);
 327
 328         return 0;
 329 }
 330
 331 /*
 332  * ipc_connect:
 333  *
 334  *   Create a UNIX domain socket and bind it to a file in /tmp.
 335  *
 336  * SECURITY: This routine is _very_ security critical since we depend on the UNIX
 337  * permissions system to prevent attackers from connecting to the socket.
 338  */
 339 static void
 340 ipc_connect (void)
 341 {
 342         struct sockaddr_un name;
 343         int sock, res;
 344         size_t size;
 345         char *filename, *directory;
 346         struct stat stat;
 347         struct passwd pwbuf;
 348         char buf [1024];
 349         struct passwd *pw;
 350
 351         if (getuid () != geteuid ()) {
 352                 fprintf (stderr, "attach: disabled listening on an IPC socket when running in setuid mode.\n");
 353                 return;
 354         }
 355
 356         /* Create the socket.   */
 357         sock = socket (PF_UNIX, SOCK_STREAM, 0);
 358         if (sock < 0) {
 359                 perror ("attach: failed to create IPC socket");
 360                 return;
 361         }
 362
 363         /*
 364          * For security reasons, create a directory to hold the listening socket,
 365          * since there is a race between bind () and chmod () below.
 366          */
 367         /* FIXME: Use TMP ? */
 368         pw = NULL;
 369 #ifdef HAVE_GETPWUID_R
 370         res = getpwuid_r (getuid (), &pwbuf, buf, sizeof (buf), &pw);
 371 #else
 372         pw = getpwuid(getuid ());
 373         res = pw != NULL ? 0 : 1;
 374 #endif
 375         if (res != 0) {
 376                 fprintf (stderr, "attach: getpwuid_r () failed.\n");
 377                 return;
 378         }
 379         g_assert (pw);
 380         directory = g_strdup_printf ("/tmp/mono-%s", pw->pw_name);
 381         res = mkdir (directory, S_IRUSR | S_IWUSR | S_IXUSR);
 382         if (res != 0) {
 383                 if (errno == EEXIST) {
 384                         /* Check type and permissions */
 385                         res = lstat (directory, &stat);
 386                         if (res != 0) {
 387                                 perror ("attach: lstat () failed");
 388                                 return;
 389                         }
 390                         if (!S_ISDIR (stat.st_mode)) {
 391                                 fprintf (stderr, "attach: path '%s' is not a directory.\n", directory);
 392                                 return;
 393                         }
 394                         if (stat.st_uid != getuid ()) {
 395                                 fprintf (stderr, "attach: directory '%s' is not owned by the current user.\n", directory);
 396                                 return;
 397                         }
 398                         if ((stat.st_mode & S_IRWXG) != 0 || (stat.st_mode & S_IRWXO) || ((stat.st_mode & S_IRWXU) != (S_IRUSR | S_IWUSR | S_IXUSR))) {
 399                                 fprintf (stderr, "attach: directory '%s' should have protection 0700.\n", directory);
 400                                 return;
 401                         }
 402                 } else {
 403                         perror ("attach: mkdir () failed");
 404                         return;
 405                 }
 406         }
 407
 408         filename = g_strdup_printf ("%s/.mono-%d", directory, getpid ());
 409         unlink (filename);
 410
 411         /* Bind a name to the socket.   */
 412         name.sun_family = AF_UNIX;
 413         strcpy (name.sun_path, filename);
 414
 415         size = (offsetof (struct sockaddr_un, sun_path)
 416                         + strlen (name.sun_path) + 1);
 417
 418         if (bind (sock, (struct sockaddr *) &name, size) < 0) {
 419                 fprintf (stderr, "attach: failed to bind IPC socket '%s': %s\n", filename, strerror (errno));
 420                 close (sock);
 421                 return;
 422         }
 423
 424         /* Set permissions */
 425         res = chmod (filename, S_IRUSR | S_IWUSR);
 426         if (res != 0) {
 427                 perror ("attach: failed to set permissions on IPC socket");
 428                 close (sock);
 429                 unlink (filename);
 430                 return;
 431         }
 432
 433         res = listen (sock, 16);
 434         if (res != 0) {
 435                 fprintf (stderr, "attach: listen () failed: %s\n", strerror (errno));
 436                 exit (1);
 437         }
 438
 439         listen_fd = sock;
 440
 441         ipc_filename = g_strdup (filename);
 442
 443         server_uri = g_strdup_printf ("unix://%s/.mono-%d?/vm", directory, getpid ());
 444
 445         g_free (filename);
 446         g_free (directory);
 447 }
 448
 449 static void
 450 transport_connect (void)
 451 {
 452         ipc_connect ();
 453 }
 454
 455 #if 0
 456
 457 static void
 458 transport_send (int fd, guint8 *data, int len)
 459 {
 460         int res;
 461
 462         stats.bytes_sent += len;
 463         //printf ("X: %d\n", stats.bytes_sent);
 464
 465         res = write (fd, data, len);
 466         if (res != len) {
 467                 /* FIXME: What to do here ? */
 468         }
 469 }
 470
 471 #endif
 472
 473 static void
 474 transport_start_receive (void)
 475 {
 476         gsize tid;
 477
 478         transport_connect ();
 479
 480         if (!listen_fd)
 481                 return;
 482
 483         receiver_thread_handle = mono_create_thread (NULL, 0, receiver_thread, NULL, 0, &tid);
 484         g_assert (receiver_thread_handle);
 485 }
 486
 487 static guint32 WINAPI
 488 receiver_thread (void *arg)
 489 {
 490         int res, content_len;
 491         guint8 buffer [256];
 492         guint8 *p, *p_end;
 493         MonoObject *exc;
 494
 495         printf ("attach: Listening on '%s'...\n", server_uri);
 496
 497         while (TRUE) {
 498                 conn_fd = accept (listen_fd, NULL, NULL);
 499                 if (conn_fd == -1)
 500                         /* Probably closed by mono_attach_cleanup () */
 501                         return 0;
 502
 503                 printf ("attach: Connected.\n");
 504
 505                 mono_thread_attach (mono_get_root_domain ());
 506                 /* Ask the runtime to not abort this thread */
 507                 //mono_thread_current ()->flags |= MONO_THREAD_FLAG_DONT_MANAGE;
 508                 /* Ask the runtime to not wait for this thread */
 509                 mono_thread_internal_current ()->state |= ThreadState_Background;
 510
 511                 while (TRUE) {
 512                         char *cmd, *agent_name, *agent_args;
 513                         guint8 *body;
 514
 515                         /* Read Header */
 516                         res = read (conn_fd, buffer, 6);
 517
 518                         if (res == -1 && errno == EINTR)
 519                                 continue;
 520
 521                         if (res == -1 || stop_receiver_thread)
 522                                 break;
 523
 524                         if (res != 6)
 525                                 break;
 526
 527                         if ((strncmp ((char*)buffer, "MONO", 4) != 0) || buffer [4] != 1 || buffer [5] != 0) {
 528                                 fprintf (stderr, "attach: message from server has unknown header.\n");
 529                                 break;
 530                         }
 531
 532                         /* Read content length */
 533                         res = read (conn_fd, buffer, 4);
 534                         if (res != 4)
 535                                 break;
 536
 537                         p = buffer;
 538                         p_end = p + 8;
 539
 540                         content_len = decode_int (p, &p, p_end);
 541
 542                         /* Read message body */
 543                         body = g_malloc (content_len);
 544                         res = read (conn_fd, body, content_len);
 545
 546                         p = body;
 547                         p_end = body + content_len;
 548
 549                         cmd = decode_string_value (p, &p, p_end);
 550                         if (cmd == NULL)
 551                                 break;
 552                         g_assert (!strcmp (cmd, "attach"));
 553
 554                         agent_name = decode_string_value (p, &p, p_end);
 555                         agent_args = decode_string_value (p, &p, p_end);
 556
 557                         printf ("attach: Loading agent '%s'.\n", agent_name);
 558                         mono_attach_load_agent (mono_domain_get (), agent_name, agent_args, &exc);
 559
 560                         g_free (body);
 561
 562                         // FIXME: Send back a result
 563                 }
 564
 565                 close (conn_fd);
 566                 conn_fd = 0;
 567
 568                 printf ("attach: Disconnected.\n");
 569
 570                 if (stop_receiver_thread)
 571                         break;
 572         }
 573
 574         return 0;
 575 }
 576
 577 #else /* DISABLE_ATTACH */
 578
 579 void
 580 mono_attach_parse_options (char *options)
 581 {
 582 }
 583
 584 void
 585 mono_attach_init (void)
 586 {
 587 }
 588
 589 gboolean
 590 mono_attach_start (void)
 591 {
 592         return FALSE;
 593 }
 594
 595 void
 596 mono_attach_maybe_start (void)
 597 {
 598 }
 599
 600 void
 601 mono_attach_cleanup (void)
 602 {
 603 }
 604
 605 #endif /* DISABLE_ATTACH */