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