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