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 #ifdef VALGRIND
  81 static
  82 int use_clone(void)
  83 {
  84         return 0;
  85 }
  86 #else
  87 static
  88 int use_clone(void)
  89 {
  90         return !getenv("LTTNG_DEBUG_NOCLONE");
  91 }
  92 #endif
  93
  94 LTTNG_HIDDEN
  95 int _utils_mkdir_recursive_unsafe(const char *path, mode_t mode);
  96
  97 /*
  98  * Create recursively directory using the FULL path.
  99  */
 100 static
 101 int _mkdir_recursive(void *_data)
 102 {
 103         struct run_as_mkdir_data *data = _data;
 104         const char *path;
 105         mode_t mode;
 106
 107         path = data->path;
 108         mode = data->mode;
 109
 110         /* Safe to call as we have transitioned to the requested uid/gid. */
 111         return _utils_mkdir_recursive_unsafe(path, mode);
 112 }
 113
 114 static
 115 int _mkdir(void *_data)
 116 {
 117         int ret;
 118         struct run_as_mkdir_data *data = _data;
 119
 120         ret = mkdir(data->path, data->mode);
 121         if (ret < 0) {
 122                 ret = -errno;
 123         }
 124
 125         return ret;
 126 }
 127
 128 static
 129 int _open(void *_data)
 130 {
 131         struct run_as_open_data *data = _data;
 132         return open(data->path, data->flags, data->mode);
 133 }
 134
 135 static
 136 int child_run_as(void *_data)
 137 {
 138         int ret;
 139         struct run_as_data *data = _data;
 140         ssize_t writelen;
 141         int sendret;
 142
 143         /*
 144          * Child: it is safe to drop egid and euid while sharing the
 145          * file descriptors with the parent process, since we do not
 146          * drop "uid": therefore, the user we are dropping egid/euid to
 147          * cannot attach to this process with, e.g. ptrace, nor map this
 148          * process memory.
 149          */
 150         if (data->gid != getegid()) {
 151                 ret = setegid(data->gid);
 152                 if (ret < 0) {
 153                         PERROR("setegid");
 154                         sendret = -1;
 155                         goto write_return;
 156                 }
 157         }
 158         if (data->uid != geteuid()) {
 159                 ret = seteuid(data->uid);
 160                 if (ret < 0) {
 161                         PERROR("seteuid");
 162                         sendret = -1;
 163                         goto write_return;
 164                 }
 165         }
 166         /*
 167          * Also set umask to 0 for mkdir executable bit.
 168          */
 169         umask(0);
 170         sendret = (*data->cmd)(data->data);
 171
 172 write_return:
 173         /* send back return value */
 174         writelen = lttng_write(data->retval_pipe, &sendret, sizeof(sendret));
 175         if (writelen < sizeof(sendret)) {
 176                 PERROR("lttng_write error");
 177                 return EXIT_FAILURE;
 178         } else {
 179                 return EXIT_SUCCESS;
 180         }
 181 }
 182
 183 static
 184 int run_as_clone(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 185 {
 186         struct run_as_data run_as_data;
 187         int ret = 0;
 188         ssize_t readlen;
 189         int status;
 190         pid_t pid;
 191         int retval_pipe[2];
 192         void *child_stack;
 193         int retval;
 194
 195         /*
 196          * If we are non-root, we can only deal with our own uid.
 197          */
 198         if (geteuid() != 0) {
 199                 if (uid != geteuid()) {
 200                         ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)",
 201                                 uid, geteuid());
 202                         return -EPERM;
 203                 }
 204         }
 205
 206         ret = pipe(retval_pipe);
 207         if (ret < 0) {
 208                 PERROR("pipe");
 209                 retval = ret;
 210                 goto end;
 211         }
 212         run_as_data.data = data;
 213         run_as_data.cmd = cmd;
 214         run_as_data.uid = uid;
 215         run_as_data.gid = gid;
 216         run_as_data.retval_pipe = retval_pipe[1];       /* write end */
 217         child_stack = mmap(NULL, RUNAS_CHILD_STACK_SIZE,
 218                 PROT_WRITE | PROT_READ,
 219                 MAP_PRIVATE | MAP_GROWSDOWN | MAP_ANONYMOUS | LTTNG_MAP_STACK,
 220                 -1, 0);
 221         if (child_stack == MAP_FAILED) {
 222                 PERROR("mmap");
 223                 retval = -ENOMEM;
 224                 goto close_pipe;
 225         }
 226         /*
 227          * Pointing to the middle of the stack to support architectures
 228          * where the stack grows up (HPPA).
 229          */
 230         pid = lttng_clone_files(child_run_as, child_stack + (RUNAS_CHILD_STACK_SIZE / 2),
 231                 &run_as_data);
 232         if (pid < 0) {
 233                 PERROR("clone");
 234                 retval = pid;
 235                 goto unmap_stack;
 236         }
 237         /* receive return value */
 238         readlen = lttng_read(retval_pipe[0], &retval, sizeof(retval));
 239         if (readlen < sizeof(retval)) {
 240                 ret = -1;
 241         }
 242
 243         /*
 244          * Parent: wait for child to return, in which case the
 245          * shared memory map will have been created.
 246          */
 247         pid = waitpid(pid, &status, 0);
 248         if (pid < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
 249                 PERROR("wait");
 250                 retval = -1;
 251         }
 252 unmap_stack:
 253         ret = munmap(child_stack, RUNAS_CHILD_STACK_SIZE);
 254         if (ret < 0) {
 255                 PERROR("munmap");
 256                 retval = ret;
 257         }
 258 close_pipe:
 259         ret = close(retval_pipe[0]);
 260         if (ret) {
 261                 PERROR("close");
 262         }
 263         ret = close(retval_pipe[1]);
 264         if (ret) {
 265                 PERROR("close");
 266         }
 267 end:
 268         return retval;
 269 }
 270
 271 /*
 272  * To be used on setups where gdb has issues debugging programs using
 273  * clone/rfork. Note that this is for debuging ONLY, and should not be
 274  * considered secure.
 275  */
 276 static
 277 int run_as_noclone(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 278 {
 279         int ret;
 280         mode_t old_mask;
 281
 282         old_mask = umask(0);
 283         ret = cmd(data);
 284         umask(old_mask);
 285
 286         return ret;
 287 }
 288
 289 static
 290 int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 291 {
 292         if (use_clone()) {
 293                 int ret;
 294
 295                 DBG("Using run_as_clone");
 296                 pthread_mutex_lock(&lttng_libc_state_lock);
 297                 ret = run_as_clone(cmd, data, uid, gid);
 298                 pthread_mutex_unlock(&lttng_libc_state_lock);
 299                 return ret;
 300         } else {
 301                 DBG("Using run_as_noclone");
 302                 return run_as_noclone(cmd, data, uid, gid);
 303         }
 304 }
 305
 306 LTTNG_HIDDEN
 307 int run_as_mkdir_recursive(const char *path, mode_t mode, uid_t uid, gid_t gid)
 308 {
 309         struct run_as_mkdir_data data;
 310
 311         DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d",
 312                         path, mode, uid, gid);
 313         data.path = path;
 314         data.mode = mode;
 315         return run_as(_mkdir_recursive, &data, uid, gid);
 316 }
 317
 318 LTTNG_HIDDEN
 319 int run_as_mkdir(const char *path, mode_t mode, uid_t uid, gid_t gid)
 320 {
 321         struct run_as_mkdir_data data;
 322
 323         DBG3("mkdir() %s with mode %d for uid %d and gid %d",
 324                         path, mode, uid, gid);
 325         data.path = path;
 326         data.mode = mode;
 327         return run_as(_mkdir, &data, uid, gid);
 328 }
 329
 330 /*
 331  * Note: open_run_as is currently not working. We'd need to pass the fd
 332  * opened in the child to the parent.
 333  */
 334 LTTNG_HIDDEN
 335 int run_as_open(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
 336 {
 337         struct run_as_open_data data;
 338
 339         DBG3("open() %s with flags %X mode %d for uid %d and gid %d",
 340                         path, flags, mode, uid, gid);
 341         data.path = path;
 342         data.flags = flags;
 343         data.mode = mode;
 344         return run_as(_open, &data, uid, gid);
 345 }