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/error.h>
  34 #include <common/compat/mman.h>
  35 #include <common/compat/clone.h>
  36
  37 #include "runas.h"
  38
  39 #define RUNAS_CHILD_STACK_SIZE  10485760
  40
  41 #ifndef MAP_STACK
  42 #define MAP_STACK               0
  43 #endif
  44
  45 #ifdef __FreeBSD__
  46 /* FreeBSD MAP_STACK always return -ENOMEM */
  47 #define LTTNG_MAP_STACK         0
  48 #else
  49 #define LTTNG_MAP_STACK         MAP_STACK
  50 #endif
  51
  52 #ifndef MAP_GROWSDOWN
  53 #define MAP_GROWSDOWN           0
  54 #endif
  55
  56 #ifndef MAP_ANONYMOUS
  57 #define MAP_ANONYMOUS           MAP_ANON
  58 #endif
  59
  60 struct run_as_data {
  61         int (*cmd)(void *data);
  62         void *data;
  63         uid_t uid;
  64         gid_t gid;
  65         int retval_pipe;
  66 };
  67
  68 struct run_as_mkdir_data {
  69         const char *path;
  70         mode_t mode;
  71 };
  72
  73 struct run_as_open_data {
  74         const char *path;
  75         int flags;
  76         mode_t mode;
  77 };
  78
  79 /*
  80  * Create recursively directory using the FULL path.
  81  */
  82 static
  83 int _mkdir_recursive(void *_data)
  84 {
  85         struct run_as_mkdir_data *data = _data;
  86         const char *path;
  87         char *p, tmp[PATH_MAX];
  88         struct stat statbuf;
  89         mode_t mode;
  90         size_t len;
  91         int ret;
  92
  93         path = data->path;
  94         mode = data->mode;
  95
  96         ret = snprintf(tmp, sizeof(tmp), "%s", path);
  97         if (ret < 0) {
  98                 PERROR("snprintf mkdir");
  99                 goto error;
 100         }
 101
 102         len = ret;
 103         if (tmp[len - 1] == '/') {
 104                 tmp[len - 1] = 0;
 105         }
 106
 107         for (p = tmp + 1; *p; p++) {
 108                 if (*p == '/') {
 109                         *p = 0;
 110                         ret = stat(tmp, &statbuf);
 111                         if (ret < 0) {
 112                                 ret = mkdir(tmp, mode);
 113                                 if (ret < 0) {
 114                                         if (!(errno == EEXIST)) {
 115                                                 PERROR("mkdir recursive");
 116                                                 ret = -errno;
 117                                                 goto error;
 118                                         }
 119                                 }
 120                         }
 121                         *p = '/';
 122                 }
 123         }
 124
 125         ret = mkdir(tmp, mode);
 126         if (ret < 0) {
 127                 if (!(errno == EEXIST)) {
 128                         PERROR("mkdir recursive last piece");
 129                         ret = -errno;
 130                 } else {
 131                         ret = 0;
 132                 }
 133         }
 134
 135 error:
 136         return ret;
 137 }
 138
 139 static
 140 int _mkdir(void *_data)
 141 {
 142         struct run_as_mkdir_data *data = _data;
 143         return mkdir(data->path, data->mode);
 144 }
 145
 146 static
 147 int _open(void *_data)
 148 {
 149         struct run_as_open_data *data = _data;
 150         return open(data->path, data->flags, data->mode);
 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         size_t writeleft, index;
 160         union {
 161                 int i;
 162                 char c[sizeof(int)];
 163         } sendret;
 164
 165         /*
 166          * Child: it is safe to drop egid and euid while sharing the
 167          * file descriptors with the parent process, since we do not
 168          * drop "uid": therefore, the user we are dropping egid/euid to
 169          * cannot attach to this process with, e.g. ptrace, nor map this
 170          * process memory.
 171          */
 172         if (data->gid != getegid()) {
 173                 ret = setegid(data->gid);
 174                 if (ret < 0) {
 175                         PERROR("setegid");
 176                         return EXIT_FAILURE;
 177                 }
 178         }
 179         if (data->uid != geteuid()) {
 180                 ret = seteuid(data->uid);
 181                 if (ret < 0) {
 182                         PERROR("seteuid");
 183                         return EXIT_FAILURE;
 184                 }
 185         }
 186         /*
 187          * Also set umask to 0 for mkdir executable bit.
 188          */
 189         umask(0);
 190         sendret.i = (*data->cmd)(data->data);
 191         /* send back return value */
 192         writeleft = sizeof(sendret);
 193         index = 0;
 194         do {
 195                 do {
 196                         writelen = write(data->retval_pipe, &sendret.c[index],
 197                                         writeleft);
 198                 } while (writelen < 0 && errno == EINTR);
 199                 if (writelen < 0) {
 200                         PERROR("write");
 201                         return EXIT_FAILURE;
 202                 }
 203                 writeleft -= writelen;
 204                 index += writelen;
 205         } while (writeleft > 0);
 206         return EXIT_SUCCESS;
 207 }
 208
 209 static
 210 int run_as_clone(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 211 {
 212         struct run_as_data run_as_data;
 213         int ret = 0;
 214         int status;
 215         pid_t pid;
 216         int retval_pipe[2];
 217         ssize_t readlen, readleft, index;
 218         void *child_stack;
 219         union {
 220                 int i;
 221                 char c[sizeof(int)];
 222         } retval;
 223
 224         /*
 225          * If we are non-root, we can only deal with our own uid.
 226          */
 227         if (geteuid() != 0) {
 228                 if (uid != geteuid()) {
 229                         ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)",
 230                                 uid, geteuid());
 231                         return -EPERM;
 232                 }
 233         }
 234
 235         ret = pipe(retval_pipe);
 236         if (ret < 0) {
 237                 PERROR("pipe");
 238                 retval.i = ret;
 239                 goto end;
 240         }
 241         run_as_data.data = data;
 242         run_as_data.cmd = cmd;
 243         run_as_data.uid = uid;
 244         run_as_data.gid = gid;
 245         run_as_data.retval_pipe = retval_pipe[1];       /* write end */
 246         child_stack = mmap(NULL, RUNAS_CHILD_STACK_SIZE,
 247                 PROT_WRITE | PROT_READ,
 248                 MAP_PRIVATE | MAP_GROWSDOWN | MAP_ANONYMOUS | LTTNG_MAP_STACK,
 249                 -1, 0);
 250         if (child_stack == MAP_FAILED) {
 251                 PERROR("mmap");
 252                 retval.i = -ENOMEM;
 253                 goto close_pipe;
 254         }
 255         /*
 256          * Pointing to the middle of the stack to support architectures
 257          * where the stack grows up (HPPA).
 258          */
 259         pid = lttng_clone_files(child_run_as, child_stack + (RUNAS_CHILD_STACK_SIZE / 2),
 260                 &run_as_data);
 261         if (pid < 0) {
 262                 PERROR("clone");
 263                 retval.i = pid;
 264                 goto unmap_stack;
 265         }
 266         /* receive return value */
 267         readleft = sizeof(retval);
 268         index = 0;
 269         do {
 270                 readlen = read(retval_pipe[0], &retval.c[index], readleft);
 271                 if (readlen < 0) {
 272                         PERROR("read");
 273                         ret = -1;
 274                         break;
 275                 }
 276                 readleft -= readlen;
 277                 index += readlen;
 278         } while (readleft > 0);
 279
 280         /*
 281          * Parent: wait for child to return, in which case the
 282          * shared memory map will have been created.
 283          */
 284         pid = waitpid(pid, &status, 0);
 285         if (pid < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
 286                 PERROR("wait");
 287                 retval.i = -1;
 288         }
 289 unmap_stack:
 290         ret = munmap(child_stack, RUNAS_CHILD_STACK_SIZE);
 291         if (ret < 0) {
 292                 PERROR("munmap");
 293                 retval.i = ret;
 294         }
 295 close_pipe:
 296         ret = close(retval_pipe[0]);
 297         if (ret) {
 298                 PERROR("close");
 299         }
 300         ret = close(retval_pipe[1]);
 301         if (ret) {
 302                 PERROR("close");
 303         }
 304 end:
 305         return retval.i;
 306 }
 307
 308 /*
 309  * To be used on setups where gdb has issues debugging programs using
 310  * clone/rfork. Note that this is for debuging ONLY, and should not be
 311  * considered secure.
 312  */
 313 static
 314 int run_as_noclone(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 315 {
 316         return cmd(data);
 317 }
 318
 319 static
 320 int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 321 {
 322         if (!getenv("LTTNG_DEBUG_NOCLONE")) {
 323                 int ret;
 324
 325                 DBG("Using run_as_clone");
 326                 pthread_mutex_lock(&lttng_libc_state_lock);
 327                 ret = run_as_clone(cmd, data, uid, gid);
 328                 pthread_mutex_unlock(&lttng_libc_state_lock);
 329                 return ret;
 330         } else {
 331                 DBG("Using run_as_noclone");
 332                 return run_as_noclone(cmd, data, uid, gid);
 333         }
 334 }
 335
 336 int run_as_mkdir_recursive(const char *path, mode_t mode, uid_t uid, gid_t gid)
 337 {
 338         struct run_as_mkdir_data data;
 339
 340         DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d",
 341                         path, mode, uid, gid);
 342         data.path = path;
 343         data.mode = mode;
 344         return run_as(_mkdir_recursive, &data, uid, gid);
 345 }
 346
 347 int run_as_mkdir(const char *path, mode_t mode, uid_t uid, gid_t gid)
 348 {
 349         struct run_as_mkdir_data data;
 350
 351         DBG3("mkdir() %s with mode %d for uid %d and gid %d",
 352                         path, mode, uid, gid);
 353         data.path = path;
 354         data.mode = mode;
 355         return run_as(_mkdir, &data, uid, gid);
 356 }
 357
 358 /*
 359  * Note: open_run_as is currently not working. We'd need to pass the fd
 360  * opened in the child to the parent.
 361  */
 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 }