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 /*
  81  * Create recursively directory using the FULL path.
  82  */
  83 static
  84 int _mkdir_recursive(void *_data)
  85 {
  86         struct run_as_mkdir_data *data = _data;
  87         const char *path;
  88         mode_t mode;
  89
  90         path = data->path;
  91         mode = data->mode;
  92
  93         return utils_mkdir_recursive(path, mode);
  94 }
  95
  96 static
  97 int _mkdir(void *_data)
  98 {
  99         int ret;
 100         struct run_as_mkdir_data *data = _data;
 101
 102         ret = mkdir(data->path, data->mode);
 103         if (ret < 0) {
 104                 ret = -errno;
 105         }
 106
 107         return ret;
 108 }
 109
 110 static
 111 int _open(void *_data)
 112 {
 113         struct run_as_open_data *data = _data;
 114         return open(data->path, data->flags, data->mode);
 115 }
 116
 117 static
 118 int child_run_as(void *_data)
 119 {
 120         int ret;
 121         struct run_as_data *data = _data;
 122         ssize_t writelen;
 123         size_t writeleft, index;
 124         union {
 125                 int i;
 126                 char c[sizeof(int)];
 127         } sendret;
 128
 129         /*
 130          * Child: it is safe to drop egid and euid while sharing the
 131          * file descriptors with the parent process, since we do not
 132          * drop "uid": therefore, the user we are dropping egid/euid to
 133          * cannot attach to this process with, e.g. ptrace, nor map this
 134          * process memory.
 135          */
 136         if (data->gid != getegid()) {
 137                 ret = setegid(data->gid);
 138                 if (ret < 0) {
 139                         PERROR("setegid");
 140                         sendret.i = -1;
 141                         goto write_return;
 142                 }
 143         }
 144         if (data->uid != geteuid()) {
 145                 ret = seteuid(data->uid);
 146                 if (ret < 0) {
 147                         PERROR("seteuid");
 148                         sendret.i = -1;
 149                         goto write_return;
 150                 }
 151         }
 152         /*
 153          * Also set umask to 0 for mkdir executable bit.
 154          */
 155         umask(0);
 156         sendret.i = (*data->cmd)(data->data);
 157
 158 write_return:
 159         /* send back return value */
 160         writeleft = sizeof(sendret);
 161         index = 0;
 162         do {
 163                 do {
 164                         writelen = write(data->retval_pipe, &sendret.c[index],
 165                                         writeleft);
 166                 } while (writelen < 0 && errno == EINTR);
 167                 if (writelen < 0) {
 168                         PERROR("write");
 169                         return EXIT_FAILURE;
 170                 }
 171                 writeleft -= writelen;
 172                 index += writelen;
 173         } while (writeleft > 0);
 174         return EXIT_SUCCESS;
 175 }
 176
 177 static
 178 int run_as_clone(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 179 {
 180         struct run_as_data run_as_data;
 181         int ret = 0;
 182         int status;
 183         pid_t pid;
 184         int retval_pipe[2];
 185         ssize_t readlen, readleft, index;
 186         void *child_stack;
 187         union {
 188                 int i;
 189                 char c[sizeof(int)];
 190         } 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.i = 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.i = -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.i = pid;
 232                 goto unmap_stack;
 233         }
 234         /* receive return value */
 235         readleft = sizeof(retval);
 236         index = 0;
 237         do {
 238                 readlen = read(retval_pipe[0], &retval.c[index], readleft);
 239                 if (readlen < 0) {
 240                         PERROR("read");
 241                         ret = -1;
 242                         break;
 243                 }
 244                 readleft -= readlen;
 245                 index += readlen;
 246         } while (readleft > 0);
 247
 248         /*
 249          * Parent: wait for child to return, in which case the
 250          * shared memory map will have been created.
 251          */
 252         pid = waitpid(pid, &status, 0);
 253         if (pid < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
 254                 PERROR("wait");
 255                 retval.i = -1;
 256         }
 257 unmap_stack:
 258         ret = munmap(child_stack, RUNAS_CHILD_STACK_SIZE);
 259         if (ret < 0) {
 260                 PERROR("munmap");
 261                 retval.i = ret;
 262         }
 263 close_pipe:
 264         ret = close(retval_pipe[0]);
 265         if (ret) {
 266                 PERROR("close");
 267         }
 268         ret = close(retval_pipe[1]);
 269         if (ret) {
 270                 PERROR("close");
 271         }
 272 end:
 273         return retval.i;
 274 }
 275
 276 /*
 277  * To be used on setups where gdb has issues debugging programs using
 278  * clone/rfork. Note that this is for debuging ONLY, and should not be
 279  * considered secure.
 280  */
 281 static
 282 int run_as_noclone(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 283 {
 284         int ret;
 285         mode_t old_mask;
 286
 287         old_mask = umask(0);
 288         ret = cmd(data);
 289         umask(old_mask);
 290
 291         return ret;
 292 }
 293
 294 static
 295 int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 296 {
 297         if (!getenv("LTTNG_DEBUG_NOCLONE")) {
 298                 int ret;
 299
 300                 DBG("Using run_as_clone");
 301                 pthread_mutex_lock(&lttng_libc_state_lock);
 302                 ret = run_as_clone(cmd, data, uid, gid);
 303                 pthread_mutex_unlock(&lttng_libc_state_lock);
 304                 return ret;
 305         } else {
 306                 DBG("Using run_as_noclone");
 307                 return run_as_noclone(cmd, data, uid, gid);
 308         }
 309 }
 310
 311 LTTNG_HIDDEN
 312 int run_as_mkdir_recursive(const char *path, mode_t mode, uid_t uid, gid_t gid)
 313 {
 314         struct run_as_mkdir_data data;
 315
 316         DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d",
 317                         path, mode, uid, gid);
 318         data.path = path;
 319         data.mode = mode;
 320         return run_as(_mkdir_recursive, &data, uid, gid);
 321 }
 322
 323 LTTNG_HIDDEN
 324 int run_as_mkdir(const char *path, mode_t mode, uid_t uid, gid_t gid)
 325 {
 326         struct run_as_mkdir_data data;
 327
 328         DBG3("mkdir() %s with mode %d for uid %d and gid %d",
 329                         path, mode, uid, gid);
 330         data.path = path;
 331         data.mode = mode;
 332         return run_as(_mkdir, &data, uid, gid);
 333 }
 334
 335 /*
 336  * Note: open_run_as is currently not working. We'd need to pass the fd
 337  * opened in the child to the parent.
 338  */
 339 LTTNG_HIDDEN
 340 int run_as_open(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
 341 {
 342         struct run_as_open_data data;
 343
 344         DBG3("open() %s with flags %X mode %d for uid %d and gid %d",
 345                         path, flags, mode, uid, gid);
 346         data.path = path;
 347         data.flags = flags;
 348         data.mode = mode;
 349         return run_as(_open, &data, uid, gid);
 350 }