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 #ifdef VALGRIND
  85 static
  86 int use_clone(void)
  87 {
  88         return 0;
  89 }
  90 #else
  91 static
  92 int use_clone(void)
  93 {
  94         return !getenv("LTTNG_DEBUG_NOCLONE");
  95 }
  96 #endif
  97
  98 LTTNG_HIDDEN
  99 int _utils_mkdir_recursive_unsafe(const char *path, mode_t mode);
 100
 101 /*
 102  * Create recursively directory using the FULL path.
 103  */
 104 static
 105 int _mkdir_recursive(void *_data)
 106 {
 107         struct run_as_mkdir_data *data = _data;
 108         const char *path;
 109         mode_t mode;
 110
 111         path = data->path;
 112         mode = data->mode;
 113
 114         /* Safe to call as we have transitioned to the requested uid/gid. */
 115         return _utils_mkdir_recursive_unsafe(path, mode);
 116 }
 117
 118 static
 119 int _mkdir(void *_data)
 120 {
 121         int ret;
 122         struct run_as_mkdir_data *data = _data;
 123
 124         ret = mkdir(data->path, data->mode);
 125         if (ret < 0) {
 126                 ret = -errno;
 127         }
 128
 129         return ret;
 130 }
 131
 132 static
 133 int _open(void *_data)
 134 {
 135         struct run_as_open_data *data = _data;
 136         return open(data->path, data->flags, data->mode);
 137 }
 138
 139 static
 140 int _unlink(void *_data)
 141 {
 142         int ret;
 143         struct run_as_unlink_data *data = _data;
 144
 145         ret = unlink(data->path);
 146         if (ret < 0) {
 147                 ret = -errno;
 148         }
 149
 150         return ret;
 151 }
 152
 153 static
 154 int child_run_as(void *_data)
 155 {
 156         int ret;
 157         struct run_as_data *data = _data;
 158         ssize_t writelen;
 159         int sendret;
 160
 161         /*
 162          * Child: it is safe to drop egid and euid while sharing the
 163          * file descriptors with the parent process, since we do not
 164          * drop "uid": therefore, the user we are dropping egid/euid to
 165          * cannot attach to this process with, e.g. ptrace, nor map this
 166          * process memory.
 167          */
 168         if (data->gid != getegid()) {
 169                 ret = setegid(data->gid);
 170                 if (ret < 0) {
 171                         PERROR("setegid");
 172                         sendret = -1;
 173                         goto write_return;
 174                 }
 175         }
 176         if (data->uid != geteuid()) {
 177                 ret = seteuid(data->uid);
 178                 if (ret < 0) {
 179                         PERROR("seteuid");
 180                         sendret = -1;
 181                         goto write_return;
 182                 }
 183         }
 184         /*
 185          * Also set umask to 0 for mkdir executable bit.
 186          */
 187         umask(0);
 188         sendret = (*data->cmd)(data->data);
 189
 190 write_return:
 191         /* send back return value */
 192         writelen = lttng_write(data->retval_pipe, &sendret, sizeof(sendret));
 193         if (writelen < sizeof(sendret)) {
 194                 PERROR("lttng_write error");
 195                 return EXIT_FAILURE;
 196         } else {
 197                 return EXIT_SUCCESS;
 198         }
 199 }
 200
 201 static
 202 int run_as_clone(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 203 {
 204         struct run_as_data run_as_data;
 205         int ret = 0;
 206         ssize_t readlen;
 207         int status;
 208         pid_t pid;
 209         int retval_pipe[2];
 210         void *child_stack;
 211         int retval;
 212
 213         /*
 214          * If we are non-root, we can only deal with our own uid.
 215          */
 216         if (geteuid() != 0) {
 217                 if (uid != geteuid()) {
 218                         ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)",
 219                                 uid, geteuid());
 220                         return -EPERM;
 221                 }
 222         }
 223
 224         ret = pipe(retval_pipe);
 225         if (ret < 0) {
 226                 PERROR("pipe");
 227                 retval = ret;
 228                 goto end;
 229         }
 230         run_as_data.data = data;
 231         run_as_data.cmd = cmd;
 232         run_as_data.uid = uid;
 233         run_as_data.gid = gid;
 234         run_as_data.retval_pipe = retval_pipe[1];       /* write end */
 235         child_stack = mmap(NULL, RUNAS_CHILD_STACK_SIZE,
 236                 PROT_WRITE | PROT_READ,
 237                 MAP_PRIVATE | MAP_GROWSDOWN | MAP_ANONYMOUS | LTTNG_MAP_STACK,
 238                 -1, 0);
 239         if (child_stack == MAP_FAILED) {
 240                 PERROR("mmap");
 241                 retval = -ENOMEM;
 242                 goto close_pipe;
 243         }
 244         /*
 245          * Pointing to the middle of the stack to support architectures
 246          * where the stack grows up (HPPA).
 247          */
 248         pid = lttng_clone_files(child_run_as, child_stack + (RUNAS_CHILD_STACK_SIZE / 2),
 249                 &run_as_data);
 250         if (pid < 0) {
 251                 PERROR("clone");
 252                 retval = pid;
 253                 goto unmap_stack;
 254         }
 255         /* receive return value */
 256         readlen = lttng_read(retval_pipe[0], &retval, sizeof(retval));
 257         if (readlen < sizeof(retval)) {
 258                 ret = -1;
 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                 PERROR("wait");
 268                 retval = -1;
 269         }
 270 unmap_stack:
 271         ret = munmap(child_stack, RUNAS_CHILD_STACK_SIZE);
 272         if (ret < 0) {
 273                 PERROR("munmap");
 274                 retval = ret;
 275         }
 276 close_pipe:
 277         ret = close(retval_pipe[0]);
 278         if (ret) {
 279                 PERROR("close");
 280         }
 281         ret = close(retval_pipe[1]);
 282         if (ret) {
 283                 PERROR("close");
 284         }
 285 end:
 286         return retval;
 287 }
 288
 289 /*
 290  * To be used on setups where gdb has issues debugging programs using
 291  * clone/rfork. Note that this is for debuging ONLY, and should not be
 292  * considered secure.
 293  */
 294 static
 295 int run_as_noclone(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 296 {
 297         int ret;
 298         mode_t old_mask;
 299
 300         old_mask = umask(0);
 301         ret = cmd(data);
 302         umask(old_mask);
 303
 304         return ret;
 305 }
 306
 307 static
 308 int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 309 {
 310         if (use_clone()) {
 311                 int ret;
 312
 313                 DBG("Using run_as_clone");
 314                 pthread_mutex_lock(&lttng_libc_state_lock);
 315                 ret = run_as_clone(cmd, data, uid, gid);
 316                 pthread_mutex_unlock(&lttng_libc_state_lock);
 317                 return ret;
 318         } else {
 319                 DBG("Using run_as_noclone");
 320                 return run_as_noclone(cmd, data, uid, gid);
 321         }
 322 }
 323
 324 LTTNG_HIDDEN
 325 int run_as_mkdir_recursive(const char *path, mode_t mode, uid_t uid, gid_t gid)
 326 {
 327         struct run_as_mkdir_data data;
 328
 329         DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d",
 330                         path, mode, uid, gid);
 331         data.path = path;
 332         data.mode = mode;
 333         return run_as(_mkdir_recursive, &data, uid, gid);
 334 }
 335
 336 LTTNG_HIDDEN
 337 int run_as_mkdir(const char *path, mode_t mode, uid_t uid, gid_t gid)
 338 {
 339         struct run_as_mkdir_data data;
 340
 341         DBG3("mkdir() %s with mode %d for uid %d and gid %d",
 342                         path, mode, uid, gid);
 343         data.path = path;
 344         data.mode = mode;
 345         return run_as(_mkdir, &data, uid, gid);
 346 }
 347
 348 /*
 349  * Note: open_run_as is currently not working. We'd need to pass the fd
 350  * opened in the child to the parent.
 351  */
 352 LTTNG_HIDDEN
 353 int run_as_open(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
 354 {
 355         struct run_as_open_data data;
 356
 357         DBG3("open() %s with flags %X mode %d for uid %d and gid %d",
 358                         path, flags, mode, uid, gid);
 359         data.path = path;
 360         data.flags = flags;
 361         data.mode = mode;
 362         return run_as(_open, &data, uid, gid);
 363 }
 364
 365 LTTNG_HIDDEN
 366 int run_as_unlink(const char *path, uid_t uid, gid_t gid)
 367 {
 368         struct run_as_unlink_data data;
 369
 370         DBG3("unlink() %s with for uid %d and gid %d",
 371              path, uid, gid);
 372         data.path = path;
 373         return run_as(_unlink, &data, uid, gid);
 374 }