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         struct run_as_data *data = _data;
 157         size_t writelen, writeleft, index;
 158         union {
 159                 int i;
 160                 char c[sizeof(int)];
 161         } sendret;
 162         int ret;
 163
 164         /*
 165          * Child: it is safe to drop egid and euid while sharing the
 166          * file descriptors with the parent process, since we do not
 167          * drop "uid": therefore, the user we are dropping egid/euid to
 168          * cannot attach to this process with, e.g. ptrace, nor map this
 169          * process memory.
 170          */
 171         if (data->gid != getegid()) {
 172                 ret = setegid(data->gid);
 173                 if (ret < 0) {
 174                         PERROR("setegid");
 175                         return EXIT_FAILURE;
 176                 }
 177         }
 178         if (data->uid != geteuid()) {
 179                 ret = seteuid(data->uid);
 180                 if (ret < 0) {
 181                         PERROR("seteuid");
 182                         return EXIT_FAILURE;
 183                 }
 184         }
 185         /*
 186          * Also set umask to 0 for mkdir executable bit.
 187          */
 188         umask(0);
 189         sendret.i = (*data->cmd)(data->data);
 190         /* send back return value */
 191         writeleft = sizeof(sendret);
 192         index = 0;
 193         do {
 194                 writelen = write(data->retval_pipe, &sendret.c[index],
 195                                 writeleft);
 196                 if (writelen < 0) {
 197                         PERROR("write");
 198                         return EXIT_FAILURE;
 199                 }
 200                 writeleft -= writelen;
 201                 index += writelen;
 202         } while (writeleft > 0);
 203         return EXIT_SUCCESS;
 204 }
 205
 206 static
 207 int run_as_clone(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 208 {
 209         struct run_as_data run_as_data;
 210         int ret = 0;
 211         int status;
 212         pid_t pid;
 213         int retval_pipe[2];
 214         ssize_t readlen, readleft, index;
 215         void *child_stack;
 216         union {
 217                 int i;
 218                 char c[sizeof(int)];
 219         } retval;
 220
 221         /*
 222          * If we are non-root, we can only deal with our own uid.
 223          */
 224         if (geteuid() != 0) {
 225                 if (uid != geteuid()) {
 226                         ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)",
 227                                 uid, geteuid());
 228                         return -EPERM;
 229                 }
 230         }
 231
 232         ret = pipe(retval_pipe);
 233         if (ret < 0) {
 234                 PERROR("pipe");
 235                 retval.i = ret;
 236                 goto end;
 237         }
 238         run_as_data.data = data;
 239         run_as_data.cmd = cmd;
 240         run_as_data.uid = uid;
 241         run_as_data.gid = gid;
 242         run_as_data.retval_pipe = retval_pipe[1];       /* write end */
 243         child_stack = mmap(NULL, RUNAS_CHILD_STACK_SIZE,
 244                 PROT_WRITE | PROT_READ,
 245                 MAP_PRIVATE | MAP_GROWSDOWN | MAP_ANONYMOUS | LTTNG_MAP_STACK,
 246                 -1, 0);
 247         if (child_stack == MAP_FAILED) {
 248                 PERROR("mmap");
 249                 retval.i = -ENOMEM;
 250                 goto close_pipe;
 251         }
 252         /*
 253          * Pointing to the middle of the stack to support architectures
 254          * where the stack grows up (HPPA).
 255          */
 256         pid = lttng_clone_files(child_run_as, child_stack + (RUNAS_CHILD_STACK_SIZE / 2),
 257                 &run_as_data);
 258         if (pid < 0) {
 259                 PERROR("clone");
 260                 retval.i = pid;
 261                 goto unmap_stack;
 262         }
 263         /* receive return value */
 264         readleft = sizeof(retval);
 265         index = 0;
 266         do {
 267                 readlen = read(retval_pipe[0], &retval.c[index], readleft);
 268                 if (readlen < 0) {
 269                         PERROR("read");
 270                         ret = -1;
 271                         break;
 272                 }
 273                 readleft -= readlen;
 274                 index += readlen;
 275         } while (readleft > 0);
 276
 277         /*
 278          * Parent: wait for child to return, in which case the
 279          * shared memory map will have been created.
 280          */
 281         pid = waitpid(pid, &status, 0);
 282         if (pid < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
 283                 PERROR("wait");
 284                 retval.i = -1;
 285         }
 286 unmap_stack:
 287         ret = munmap(child_stack, RUNAS_CHILD_STACK_SIZE);
 288         if (ret < 0) {
 289                 PERROR("munmap");
 290                 retval.i = ret;
 291         }
 292 close_pipe:
 293         ret = close(retval_pipe[0]);
 294         if (ret) {
 295                 PERROR("close");
 296         }
 297         ret = close(retval_pipe[1]);
 298         if (ret) {
 299                 PERROR("close");
 300         }
 301 end:
 302         return retval.i;
 303 }
 304
 305 /*
 306  * To be used on setups where gdb has issues debugging programs using
 307  * clone/rfork. Note that this is for debuging ONLY, and should not be
 308  * considered secure.
 309  */
 310 static
 311 int run_as_noclone(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 312 {
 313         return cmd(data);
 314 }
 315
 316 static
 317 int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 318 {
 319         if (!getenv("LTTNG_DEBUG_NOCLONE")) {
 320                 int ret;
 321
 322                 DBG("Using run_as_clone");
 323                 pthread_mutex_lock(&lttng_libc_state_lock);
 324                 ret = run_as_clone(cmd, data, uid, gid);
 325                 pthread_mutex_unlock(&lttng_libc_state_lock);
 326                 return ret;
 327         } else {
 328                 DBG("Using run_as_noclone");
 329                 return run_as_noclone(cmd, data, uid, gid);
 330         }
 331 }
 332
 333 int run_as_mkdir_recursive(const char *path, mode_t mode, uid_t uid, gid_t gid)
 334 {
 335         struct run_as_mkdir_data data;
 336
 337         DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d",
 338                         path, mode, uid, gid);
 339         data.path = path;
 340         data.mode = mode;
 341         return run_as(_mkdir_recursive, &data, uid, gid);
 342 }
 343
 344 int run_as_mkdir(const char *path, mode_t mode, uid_t uid, gid_t gid)
 345 {
 346         struct run_as_mkdir_data data;
 347
 348         DBG3("mkdir() %s with mode %d for uid %d and gid %d",
 349                         path, mode, uid, gid);
 350         data.path = path;
 351         data.mode = mode;
 352         return run_as(_mkdir, &data, uid, gid);
 353 }
 354
 355 /*
 356  * Note: open_run_as is currently not working. We'd need to pass the fd
 357  * opened in the child to the parent.
 358  */
 359 int run_as_open(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
 360 {
 361         struct run_as_open_data data;
 362
 363         DBG3("open() %s with flags %X mode %d for uid %d and gid %d",
 364                         path, flags, mode, uid, gid);
 365         data.path = path;
 366         data.flags = flags;
 367         data.mode = mode;
 368         return run_as(_open, &data, uid, gid);
 369 }