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