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 #ifdef __FreeBSD__
  42 /* FreeBSD MAP_STACK always return -ENOMEM */
  43 #define LTTNG_MAP_STACK         0
  44 #else
  45 #define LTTNG_MAP_STACK         MAP_STACK
  46 #endif
  47
  48 #ifndef MAP_GROWSDOWN
  49 #define MAP_GROWSDOWN           0
  50 #endif
  51
  52 #ifndef MAP_ANONYMOUS
  53 #define MAP_ANONYMOUS           MAP_ANON
  54 #endif
  55
  56 struct run_as_data {
  57         int (*cmd)(void *data);
  58         void *data;
  59         uid_t uid;
  60         gid_t gid;
  61         int retval_pipe;
  62 };
  63
  64 struct run_as_mkdir_data {
  65         const char *path;
  66         mode_t mode;
  67 };
  68
  69 struct run_as_open_data {
  70         const char *path;
  71         int flags;
  72         mode_t mode;
  73 };
  74
  75 /*
  76  * Create recursively directory using the FULL path.
  77  */
  78 static
  79 int _mkdir_recursive(void *_data)
  80 {
  81         struct run_as_mkdir_data *data = _data;
  82         const char *path;
  83         char *p, tmp[PATH_MAX];
  84         struct stat statbuf;
  85         mode_t mode;
  86         size_t len;
  87         int ret;
  88
  89         path = data->path;
  90         mode = data->mode;
  91
  92         ret = snprintf(tmp, sizeof(tmp), "%s", path);
  93         if (ret < 0) {
  94                 PERROR("snprintf mkdir");
  95                 goto error;
  96         }
  97
  98         len = ret;
  99         if (tmp[len - 1] == '/') {
 100                 tmp[len - 1] = 0;
 101         }
 102
 103         for (p = tmp + 1; *p; p++) {
 104                 if (*p == '/') {
 105                         *p = 0;
 106                         ret = stat(tmp, &statbuf);
 107                         if (ret < 0) {
 108                                 ret = mkdir(tmp, mode);
 109                                 if (ret < 0) {
 110                                         if (!(errno == EEXIST)) {
 111                                                 PERROR("mkdir recursive");
 112                                                 ret = -errno;
 113                                                 goto error;
 114                                         }
 115                                 }
 116                         }
 117                         *p = '/';
 118                 }
 119         }
 120
 121         ret = mkdir(tmp, mode);
 122         if (ret < 0) {
 123                 if (!(errno == EEXIST)) {
 124                         PERROR("mkdir recursive last piece");
 125                         ret = -errno;
 126                 } else {
 127                         ret = 0;
 128                 }
 129         }
 130
 131 error:
 132         return ret;
 133 }
 134
 135 static
 136 int _mkdir(void *_data)
 137 {
 138         struct run_as_mkdir_data *data = _data;
 139         return mkdir(data->path, data->mode);
 140 }
 141
 142 static
 143 int _open(void *_data)
 144 {
 145         struct run_as_open_data *data = _data;
 146         return open(data->path, data->flags, data->mode);
 147 }
 148
 149 static
 150 int child_run_as(void *_data)
 151 {
 152         struct run_as_data *data = _data;
 153         size_t writelen, writeleft, index;
 154         union {
 155                 int i;
 156                 char c[sizeof(int)];
 157         } sendret;
 158         int ret;
 159
 160         /*
 161          * Child: it is safe to drop egid and euid while sharing the
 162          * file descriptors with the parent process, since we do not
 163          * drop "uid": therefore, the user we are dropping egid/euid to
 164          * cannot attach to this process with, e.g. ptrace, nor map this
 165          * process memory.
 166          */
 167         if (data->gid != getegid()) {
 168                 ret = setegid(data->gid);
 169                 if (ret < 0) {
 170                         PERROR("setegid");
 171                         return EXIT_FAILURE;
 172                 }
 173         }
 174         if (data->uid != geteuid()) {
 175                 ret = seteuid(data->uid);
 176                 if (ret < 0) {
 177                         PERROR("seteuid");
 178                         return EXIT_FAILURE;
 179                 }
 180         }
 181         /*
 182          * Also set umask to 0 for mkdir executable bit.
 183          */
 184         umask(0);
 185         sendret.i = (*data->cmd)(data->data);
 186         /* send back return value */
 187         writeleft = sizeof(sendret);
 188         index = 0;
 189         do {
 190                 writelen = write(data->retval_pipe, &sendret.c[index],
 191                                 writeleft);
 192                 if (writelen < 0) {
 193                         PERROR("write");
 194                         return EXIT_FAILURE;
 195                 }
 196                 writeleft -= writelen;
 197                 index += writelen;
 198         } while (writeleft > 0);
 199         return EXIT_SUCCESS;
 200 }
 201
 202 static
 203 int run_as_clone(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 204 {
 205         struct run_as_data run_as_data;
 206         int ret = 0;
 207         int status;
 208         pid_t pid;
 209         int retval_pipe[2];
 210         ssize_t readlen, readleft, index;
 211         void *child_stack;
 212         union {
 213                 int i;
 214                 char c[sizeof(int)];
 215         } retval;
 216
 217         /*
 218          * If we are non-root, we can only deal with our own uid.
 219          */
 220         if (geteuid() != 0) {
 221                 if (uid != geteuid()) {
 222                         ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)",
 223                                 uid, geteuid());
 224                         return -EPERM;
 225                 }
 226         }
 227
 228         ret = pipe(retval_pipe);
 229         if (ret < 0) {
 230                 PERROR("pipe");
 231                 retval.i = ret;
 232                 goto end;
 233         }
 234         run_as_data.data = data;
 235         run_as_data.cmd = cmd;
 236         run_as_data.uid = uid;
 237         run_as_data.gid = gid;
 238         run_as_data.retval_pipe = retval_pipe[1];       /* write end */
 239         child_stack = mmap(NULL, RUNAS_CHILD_STACK_SIZE,
 240                 PROT_WRITE | PROT_READ,
 241                 MAP_PRIVATE | MAP_GROWSDOWN | MAP_ANONYMOUS | LTTNG_MAP_STACK,
 242                 -1, 0);
 243         if (child_stack == MAP_FAILED) {
 244                 PERROR("mmap");
 245                 retval.i = -ENOMEM;
 246                 goto close_pipe;
 247         }
 248         /*
 249          * Pointing to the middle of the stack to support architectures
 250          * where the stack grows up (HPPA).
 251          */
 252         pid = lttng_clone_files(child_run_as, child_stack + (RUNAS_CHILD_STACK_SIZE / 2),
 253                 &run_as_data);
 254         if (pid < 0) {
 255                 PERROR("clone");
 256                 retval.i = pid;
 257                 goto unmap_stack;
 258         }
 259         /* receive return value */
 260         readleft = sizeof(retval);
 261         index = 0;
 262         do {
 263                 readlen = read(retval_pipe[0], &retval.c[index], readleft);
 264                 if (readlen < 0) {
 265                         PERROR("read");
 266                         ret = -1;
 267                         break;
 268                 }
 269                 readleft -= readlen;
 270                 index += readlen;
 271         } while (readleft > 0);
 272
 273         /*
 274          * Parent: wait for child to return, in which case the
 275          * shared memory map will have been created.
 276          */
 277         pid = waitpid(pid, &status, 0);
 278         if (pid < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
 279                 PERROR("wait");
 280                 retval.i = -1;
 281         }
 282 unmap_stack:
 283         ret = munmap(child_stack, RUNAS_CHILD_STACK_SIZE);
 284         if (ret < 0) {
 285                 PERROR("munmap");
 286                 retval.i = ret;
 287         }
 288 close_pipe:
 289         ret = close(retval_pipe[0]);
 290         if (ret) {
 291                 PERROR("close");
 292         }
 293         ret = close(retval_pipe[1]);
 294         if (ret) {
 295                 PERROR("close");
 296         }
 297 end:
 298         return retval.i;
 299 }
 300
 301 /*
 302  * To be used on setups where gdb has issues debugging programs using
 303  * clone/rfork. Note that this is for debuging ONLY, and should not be
 304  * considered secure.
 305  */
 306 static
 307 int run_as_noclone(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 308 {
 309         return cmd(data);
 310 }
 311
 312 static
 313 int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 314 {
 315         if (!getenv("LTTNG_DEBUG_NOCLONE")) {
 316                 DBG("Using run_as_clone");
 317                 return run_as_clone(cmd, data, uid, gid);
 318         } else {
 319                 DBG("Using run_as_noclone");
 320                 return run_as_noclone(cmd, data, uid, gid);
 321         }
 322 }
 323
 324 int run_as_mkdir_recursive(const char *path, mode_t mode, uid_t uid, gid_t gid)
 325 {
 326         struct run_as_mkdir_data data;
 327
 328         DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d",
 329                         path, mode, uid, gid);
 330         data.path = path;
 331         data.mode = mode;
 332         return run_as(_mkdir_recursive, &data, uid, gid);
 333 }
 334
 335 int run_as_mkdir(const char *path, mode_t mode, uid_t uid, gid_t gid)
 336 {
 337         struct run_as_mkdir_data data;
 338
 339         DBG3("mkdir() %s with mode %d for uid %d and gid %d",
 340                         path, mode, uid, gid);
 341         data.path = path;
 342         data.mode = mode;
 343         return run_as(_mkdir, &data, uid, gid);
 344 }
 345
 346 /*
 347  * Note: open_run_as is currently not working. We'd need to pass the fd
 348  * opened in the child to the parent.
 349  */
 350 int run_as_open(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
 351 {
 352         struct run_as_open_data data;
 353
 354         DBG3("open() %s with flags %X mode %d for uid %d and gid %d",
 355                         path, flags, mode, uid, gid);
 356         data.path = path;
 357         data.flags = flags;
 358         data.mode = mode;
 359         return run_as(_open, &data, uid, gid);
 360 }