src/common/runas.c

   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(&lttng_libc_state_lock);
 324                 ret = run_as_clone(cmd, data, uid, gid);
 325                 pthread_mutex_unlock(&lttng_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 }