| 1 | /* |
| 2 | * Copyright (C) 2011 - David Goulet <david.goulet@polymtl.ca> |
| 3 | * Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
| 4 | * |
| 5 | * This program is free software; you can redistribute it and/or modify |
| 6 | * it under the terms of the GNU General Public License, version 2 only, |
| 7 | * as published by the Free Software Foundation. |
| 8 | * |
| 9 | * This program 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 for |
| 12 | * more details. |
| 13 | * |
| 14 | * You should have received a copy of the GNU General Public License along |
| 15 | * with this program; if not, write to the Free Software Foundation, Inc., |
| 16 | * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. |
| 17 | */ |
| 18 | |
| 19 | #define _GNU_SOURCE |
| 20 | #include <errno.h> |
| 21 | #include <limits.h> |
| 22 | #include <stdio.h> |
| 23 | #include <stdlib.h> |
| 24 | #include <string.h> |
| 25 | #include <sys/wait.h> |
| 26 | #include <sys/types.h> |
| 27 | #include <sys/stat.h> |
| 28 | #include <unistd.h> |
| 29 | #include <fcntl.h> |
| 30 | #include <sched.h> |
| 31 | #include <sys/signal.h> |
| 32 | |
| 33 | #include <common/common.h> |
| 34 | #include <common/utils.h> |
| 35 | #include <common/compat/mman.h> |
| 36 | #include <common/compat/clone.h> |
| 37 | |
| 38 | #include "runas.h" |
| 39 | |
| 40 | #define RUNAS_CHILD_STACK_SIZE 10485760 |
| 41 | |
| 42 | #ifndef MAP_STACK |
| 43 | #define MAP_STACK 0 |
| 44 | #endif |
| 45 | |
| 46 | #ifdef __FreeBSD__ |
| 47 | /* FreeBSD MAP_STACK always return -ENOMEM */ |
| 48 | #define LTTNG_MAP_STACK 0 |
| 49 | #else |
| 50 | #define LTTNG_MAP_STACK MAP_STACK |
| 51 | #endif |
| 52 | |
| 53 | #ifndef MAP_GROWSDOWN |
| 54 | #define MAP_GROWSDOWN 0 |
| 55 | #endif |
| 56 | |
| 57 | #ifndef MAP_ANONYMOUS |
| 58 | #define MAP_ANONYMOUS MAP_ANON |
| 59 | #endif |
| 60 | |
| 61 | struct run_as_data { |
| 62 | int (*cmd)(void *data); |
| 63 | void *data; |
| 64 | uid_t uid; |
| 65 | gid_t gid; |
| 66 | int retval_pipe; |
| 67 | }; |
| 68 | |
| 69 | struct run_as_mkdir_data { |
| 70 | const char *path; |
| 71 | mode_t mode; |
| 72 | }; |
| 73 | |
| 74 | struct run_as_open_data { |
| 75 | const char *path; |
| 76 | int flags; |
| 77 | mode_t mode; |
| 78 | }; |
| 79 | |
| 80 | struct run_as_unlink_data { |
| 81 | const char *path; |
| 82 | }; |
| 83 | |
| 84 | struct run_as_ret { |
| 85 | int ret; |
| 86 | int _errno; |
| 87 | }; |
| 88 | |
| 89 | #ifdef VALGRIND |
| 90 | static |
| 91 | int use_clone(void) |
| 92 | { |
| 93 | return 0; |
| 94 | } |
| 95 | #else |
| 96 | static |
| 97 | int use_clone(void) |
| 98 | { |
| 99 | return !getenv("LTTNG_DEBUG_NOCLONE"); |
| 100 | } |
| 101 | #endif |
| 102 | |
| 103 | LTTNG_HIDDEN |
| 104 | int _utils_mkdir_recursive_unsafe(const char *path, mode_t mode); |
| 105 | |
| 106 | /* |
| 107 | * Create recursively directory using the FULL path. |
| 108 | */ |
| 109 | static |
| 110 | int _mkdir_recursive(void *_data) |
| 111 | { |
| 112 | struct run_as_mkdir_data *data = _data; |
| 113 | const char *path; |
| 114 | mode_t mode; |
| 115 | |
| 116 | path = data->path; |
| 117 | mode = data->mode; |
| 118 | |
| 119 | /* Safe to call as we have transitioned to the requested uid/gid. */ |
| 120 | return _utils_mkdir_recursive_unsafe(path, mode); |
| 121 | } |
| 122 | |
| 123 | static |
| 124 | int _mkdir(void *_data) |
| 125 | { |
| 126 | struct run_as_mkdir_data *data = _data; |
| 127 | |
| 128 | return mkdir(data->path, data->mode); |
| 129 | } |
| 130 | |
| 131 | static |
| 132 | int _open(void *_data) |
| 133 | { |
| 134 | struct run_as_open_data *data = _data; |
| 135 | |
| 136 | return open(data->path, data->flags, data->mode); |
| 137 | } |
| 138 | |
| 139 | static |
| 140 | int _unlink(void *_data) |
| 141 | { |
| 142 | struct run_as_unlink_data *data = _data; |
| 143 | |
| 144 | return unlink(data->path); |
| 145 | } |
| 146 | |
| 147 | static |
| 148 | int child_run_as(void *_data) |
| 149 | { |
| 150 | int ret; |
| 151 | struct run_as_data *data = _data; |
| 152 | ssize_t writelen; |
| 153 | struct run_as_ret sendret; |
| 154 | |
| 155 | /* |
| 156 | * Child: it is safe to drop egid and euid while sharing the |
| 157 | * file descriptors with the parent process, since we do not |
| 158 | * drop "uid": therefore, the user we are dropping egid/euid to |
| 159 | * cannot attach to this process with, e.g. ptrace, nor map this |
| 160 | * process memory. |
| 161 | */ |
| 162 | if (data->gid != getegid()) { |
| 163 | ret = setegid(data->gid); |
| 164 | if (ret < 0) { |
| 165 | PERROR("setegid"); |
| 166 | goto write_return; |
| 167 | } |
| 168 | } |
| 169 | if (data->uid != geteuid()) { |
| 170 | ret = seteuid(data->uid); |
| 171 | if (ret < 0) { |
| 172 | PERROR("seteuid"); |
| 173 | goto write_return; |
| 174 | } |
| 175 | } |
| 176 | /* |
| 177 | * Also set umask to 0 for mkdir executable bit. |
| 178 | */ |
| 179 | umask(0); |
| 180 | ret = (*data->cmd)(data->data); |
| 181 | |
| 182 | write_return: |
| 183 | sendret.ret = ret; |
| 184 | sendret._errno = errno; |
| 185 | /* send back return value */ |
| 186 | writelen = lttng_write(data->retval_pipe, &sendret, sizeof(sendret)); |
| 187 | if (writelen < sizeof(sendret)) { |
| 188 | PERROR("lttng_write error"); |
| 189 | return EXIT_FAILURE; |
| 190 | } else { |
| 191 | return EXIT_SUCCESS; |
| 192 | } |
| 193 | } |
| 194 | |
| 195 | static |
| 196 | int run_as_clone(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid) |
| 197 | { |
| 198 | struct run_as_data run_as_data; |
| 199 | int ret = 0; |
| 200 | ssize_t readlen; |
| 201 | int status; |
| 202 | pid_t pid; |
| 203 | int retval_pipe[2]; |
| 204 | void *child_stack; |
| 205 | struct run_as_ret recvret; |
| 206 | |
| 207 | /* |
| 208 | * If we are non-root, we can only deal with our own uid. |
| 209 | */ |
| 210 | if (geteuid() != 0) { |
| 211 | if (uid != geteuid()) { |
| 212 | recvret.ret = -1; |
| 213 | recvret._errno = EPERM; |
| 214 | ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)", |
| 215 | uid, geteuid()); |
| 216 | goto end; |
| 217 | } |
| 218 | } |
| 219 | |
| 220 | ret = pipe(retval_pipe); |
| 221 | if (ret < 0) { |
| 222 | recvret.ret = -1; |
| 223 | recvret._errno = errno; |
| 224 | PERROR("pipe"); |
| 225 | goto end; |
| 226 | } |
| 227 | run_as_data.data = data; |
| 228 | run_as_data.cmd = cmd; |
| 229 | run_as_data.uid = uid; |
| 230 | run_as_data.gid = gid; |
| 231 | run_as_data.retval_pipe = retval_pipe[1]; /* write end */ |
| 232 | child_stack = mmap(NULL, RUNAS_CHILD_STACK_SIZE, |
| 233 | PROT_WRITE | PROT_READ, |
| 234 | MAP_PRIVATE | MAP_GROWSDOWN | MAP_ANONYMOUS | LTTNG_MAP_STACK, |
| 235 | -1, 0); |
| 236 | if (child_stack == MAP_FAILED) { |
| 237 | recvret.ret = -1; |
| 238 | recvret._errno = ENOMEM; |
| 239 | PERROR("mmap"); |
| 240 | goto close_pipe; |
| 241 | } |
| 242 | /* |
| 243 | * Pointing to the middle of the stack to support architectures |
| 244 | * where the stack grows up (HPPA). |
| 245 | */ |
| 246 | pid = lttng_clone_files(child_run_as, child_stack + (RUNAS_CHILD_STACK_SIZE / 2), |
| 247 | &run_as_data); |
| 248 | if (pid < 0) { |
| 249 | recvret.ret = -1; |
| 250 | recvret._errno = errno; |
| 251 | PERROR("clone"); |
| 252 | goto unmap_stack; |
| 253 | } |
| 254 | /* receive return value */ |
| 255 | readlen = lttng_read(retval_pipe[0], &recvret, sizeof(recvret)); |
| 256 | if (readlen < sizeof(recvret)) { |
| 257 | recvret.ret = -1; |
| 258 | recvret._errno = errno; |
| 259 | } |
| 260 | |
| 261 | /* |
| 262 | * Parent: wait for child to return, in which case the |
| 263 | * shared memory map will have been created. |
| 264 | */ |
| 265 | pid = waitpid(pid, &status, 0); |
| 266 | if (pid < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) { |
| 267 | recvret.ret = -1; |
| 268 | recvret._errno = errno; |
| 269 | PERROR("wait"); |
| 270 | } |
| 271 | unmap_stack: |
| 272 | ret = munmap(child_stack, RUNAS_CHILD_STACK_SIZE); |
| 273 | if (ret < 0) { |
| 274 | recvret.ret = -1; |
| 275 | recvret._errno = errno; |
| 276 | PERROR("munmap"); |
| 277 | } |
| 278 | close_pipe: |
| 279 | ret = close(retval_pipe[0]); |
| 280 | if (ret) { |
| 281 | recvret.ret = -1; |
| 282 | recvret._errno = errno; |
| 283 | PERROR("close"); |
| 284 | } |
| 285 | ret = close(retval_pipe[1]); |
| 286 | if (ret) { |
| 287 | recvret.ret = -1; |
| 288 | recvret._errno = errno; |
| 289 | PERROR("close"); |
| 290 | } |
| 291 | end: |
| 292 | errno = recvret._errno; |
| 293 | return recvret.ret; |
| 294 | } |
| 295 | |
| 296 | /* |
| 297 | * To be used on setups where gdb has issues debugging programs using |
| 298 | * clone/rfork. Note that this is for debuging ONLY, and should not be |
| 299 | * considered secure. |
| 300 | */ |
| 301 | static |
| 302 | int run_as_noclone(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid) |
| 303 | { |
| 304 | int ret, saved_errno; |
| 305 | mode_t old_mask; |
| 306 | |
| 307 | old_mask = umask(0); |
| 308 | ret = cmd(data); |
| 309 | saved_errno = errno; |
| 310 | umask(old_mask); |
| 311 | errno = saved_errno; |
| 312 | |
| 313 | return ret; |
| 314 | } |
| 315 | |
| 316 | static |
| 317 | int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid) |
| 318 | { |
| 319 | if (use_clone()) { |
| 320 | int ret; |
| 321 | |
| 322 | DBG("Using run_as_clone"); |
| 323 | pthread_mutex_lock(<tng_libc_state_lock); |
| 324 | ret = run_as_clone(cmd, data, uid, gid); |
| 325 | pthread_mutex_unlock(<tng_libc_state_lock); |
| 326 | return ret; |
| 327 | } else { |
| 328 | DBG("Using run_as_noclone"); |
| 329 | return run_as_noclone(cmd, data, uid, gid); |
| 330 | } |
| 331 | } |
| 332 | |
| 333 | LTTNG_HIDDEN |
| 334 | int run_as_mkdir_recursive(const char *path, mode_t mode, uid_t uid, gid_t gid) |
| 335 | { |
| 336 | struct run_as_mkdir_data data; |
| 337 | |
| 338 | DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d", |
| 339 | path, mode, uid, gid); |
| 340 | data.path = path; |
| 341 | data.mode = mode; |
| 342 | return run_as(_mkdir_recursive, &data, uid, gid); |
| 343 | } |
| 344 | |
| 345 | LTTNG_HIDDEN |
| 346 | int run_as_mkdir(const char *path, mode_t mode, uid_t uid, gid_t gid) |
| 347 | { |
| 348 | struct run_as_mkdir_data data; |
| 349 | |
| 350 | DBG3("mkdir() %s with mode %d for uid %d and gid %d", |
| 351 | path, mode, uid, gid); |
| 352 | data.path = path; |
| 353 | data.mode = mode; |
| 354 | return run_as(_mkdir, &data, uid, gid); |
| 355 | } |
| 356 | |
| 357 | /* |
| 358 | * Note: open_run_as is currently not working. We'd need to pass the fd |
| 359 | * opened in the child to the parent. |
| 360 | */ |
| 361 | LTTNG_HIDDEN |
| 362 | int run_as_open(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid) |
| 363 | { |
| 364 | struct run_as_open_data data; |
| 365 | |
| 366 | DBG3("open() %s with flags %X mode %d for uid %d and gid %d", |
| 367 | path, flags, mode, uid, gid); |
| 368 | data.path = path; |
| 369 | data.flags = flags; |
| 370 | data.mode = mode; |
| 371 | return run_as(_open, &data, uid, gid); |
| 372 | } |
| 373 | |
| 374 | LTTNG_HIDDEN |
| 375 | int run_as_unlink(const char *path, uid_t uid, gid_t gid) |
| 376 | { |
| 377 | struct run_as_unlink_data data; |
| 378 | |
| 379 | DBG3("unlink() %s with for uid %d and gid %d", |
| 380 | path, uid, gid); |
| 381 | data.path = path; |
| 382 | return run_as(_unlink, &data, uid, gid); |
| 383 | } |