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 #define _LGPL_SOURCE
  21 #include <errno.h>
  22 #include <limits.h>
  23 #include <stdio.h>
  24 #include <stdlib.h>
  25 #include <string.h>
  26 #include <sys/wait.h>
  27 #include <sys/types.h>
  28 #include <sys/stat.h>
  29 #include <unistd.h>
  30 #include <fcntl.h>
  31 #include <sched.h>
  32 #include <sys/signal.h>
  33
  34 #include <common/common.h>
  35 #include <common/utils.h>
  36 #include <common/compat/mman.h>
  37 #include <common/compat/clone.h>
  38 #include <common/compat/getenv.h>
  39
  40 #include "runas.h"
  41
  42 #define RUNAS_CHILD_STACK_SIZE  10485760
  43
  44 #ifndef MAP_STACK
  45 #define MAP_STACK               0
  46 #endif
  47
  48 #ifdef __FreeBSD__
  49 /* FreeBSD MAP_STACK always return -ENOMEM */
  50 #define LTTNG_MAP_STACK         0
  51 #else
  52 #define LTTNG_MAP_STACK         MAP_STACK
  53 #endif
  54
  55 #ifndef MAP_GROWSDOWN
  56 #define MAP_GROWSDOWN           0
  57 #endif
  58
  59 #ifndef MAP_ANONYMOUS
  60 #define MAP_ANONYMOUS           MAP_ANON
  61 #endif
  62
  63 struct run_as_data {
  64         int (*cmd)(void *data);
  65         void *data;
  66         uid_t uid;
  67         gid_t gid;
  68         int retval_pipe;
  69 };
  70
  71 struct run_as_mkdir_data {
  72         const char *path;
  73         mode_t mode;
  74 };
  75
  76 struct run_as_open_data {
  77         const char *path;
  78         int flags;
  79         mode_t mode;
  80 };
  81
  82 #ifdef VALGRIND
  83 static
  84 int use_clone(void)
  85 {
  86         return 0;
  87 }
  88 #else
  89 static
  90 int use_clone(void)
  91 {
  92         return !lttng_secure_getenv("LTTNG_DEBUG_NOCLONE");
  93 }
  94 #endif
  95
  96 /*
  97  * Create recursively directory using the FULL path.
  98  */
  99 static
 100 int _mkdir_recursive(void *_data)
 101 {
 102         struct run_as_mkdir_data *data = _data;
 103         const char *path;
 104         mode_t mode;
 105
 106         path = data->path;
 107         mode = data->mode;
 108
 109         return utils_mkdir_recursive(path, mode);
 110 }
 111
 112 static
 113 int _mkdir(void *_data)
 114 {
 115         int ret;
 116         struct run_as_mkdir_data *data = _data;
 117
 118         ret = mkdir(data->path, data->mode);
 119         if (ret < 0) {
 120                 ret = -errno;
 121         }
 122
 123         return ret;
 124 }
 125
 126 static
 127 int _open(void *_data)
 128 {
 129         struct run_as_open_data *data = _data;
 130         return open(data->path, data->flags, data->mode);
 131 }
 132
 133 static
 134 int child_run_as(void *_data)
 135 {
 136         int ret;
 137         struct run_as_data *data = _data;
 138         ssize_t writelen;
 139         int sendret;
 140
 141         /*
 142          * Child: it is safe to drop egid and euid while sharing the
 143          * file descriptors with the parent process, since we do not
 144          * drop "uid": therefore, the user we are dropping egid/euid to
 145          * cannot attach to this process with, e.g. ptrace, nor map this
 146          * process memory.
 147          */
 148         if (data->gid != getegid()) {
 149                 ret = setegid(data->gid);
 150                 if (ret < 0) {
 151                         PERROR("setegid");
 152                         sendret = -1;
 153                         goto write_return;
 154                 }
 155         }
 156         if (data->uid != geteuid()) {
 157                 ret = seteuid(data->uid);
 158                 if (ret < 0) {
 159                         PERROR("seteuid");
 160                         sendret = -1;
 161                         goto write_return;
 162                 }
 163         }
 164         /*
 165          * Also set umask to 0 for mkdir executable bit.
 166          */
 167         umask(0);
 168         sendret = (*data->cmd)(data->data);
 169
 170 write_return:
 171         /* send back return value */
 172         writelen = lttng_write(data->retval_pipe, &sendret, sizeof(sendret));
 173         if (writelen < sizeof(sendret)) {
 174                 PERROR("lttng_write error");
 175                 return EXIT_FAILURE;
 176         } else {
 177                 return EXIT_SUCCESS;
 178         }
 179 }
 180
 181 static
 182 int run_as_clone(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 183 {
 184         struct run_as_data run_as_data;
 185         int ret = 0;
 186         ssize_t readlen;
 187         int status;
 188         pid_t pid;
 189         int retval_pipe[2];
 190         void *child_stack;
 191         int retval;
 192
 193         /*
 194          * If we are non-root, we can only deal with our own uid.
 195          */
 196         if (geteuid() != 0) {
 197                 if (uid != geteuid()) {
 198                         ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)",
 199                                 uid, geteuid());
 200                         return -EPERM;
 201                 }
 202         }
 203
 204         ret = pipe(retval_pipe);
 205         if (ret < 0) {
 206                 PERROR("pipe");
 207                 retval = ret;
 208                 goto end;
 209         }
 210         run_as_data.data = data;
 211         run_as_data.cmd = cmd;
 212         run_as_data.uid = uid;
 213         run_as_data.gid = gid;
 214         run_as_data.retval_pipe = retval_pipe[1];       /* write end */
 215         child_stack = mmap(NULL, RUNAS_CHILD_STACK_SIZE,
 216                 PROT_WRITE | PROT_READ,
 217                 MAP_PRIVATE | MAP_GROWSDOWN | MAP_ANONYMOUS | LTTNG_MAP_STACK,
 218                 -1, 0);
 219         if (child_stack == MAP_FAILED) {
 220                 PERROR("mmap");
 221                 retval = -ENOMEM;
 222                 goto close_pipe;
 223         }
 224         /*
 225          * Pointing to the middle of the stack to support architectures
 226          * where the stack grows up (HPPA).
 227          */
 228         pid = lttng_clone_files(child_run_as, child_stack + (RUNAS_CHILD_STACK_SIZE / 2),
 229                 &run_as_data);
 230         if (pid < 0) {
 231                 PERROR("clone");
 232                 retval = pid;
 233                 goto unmap_stack;
 234         }
 235         /* receive return value */
 236         readlen = lttng_read(retval_pipe[0], &retval, sizeof(retval));
 237         if (readlen < sizeof(retval)) {
 238                 ret = -1;
 239         }
 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 = -1;
 249         }
 250 unmap_stack:
 251         ret = munmap(child_stack, RUNAS_CHILD_STACK_SIZE);
 252         if (ret < 0) {
 253                 PERROR("munmap");
 254                 retval = 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;
 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 (use_clone()) {
 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 }