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