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 it
   6  * under the terms of the GNU General Public License as published by the Free
   7  * Software Foundation; only version 2 of the License.
   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 with
  15  * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
  16  * Place - Suite 330, Boston, MA  02111-1307, 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/mman.h>
  32
  33 #include <lttngerr.h>
  34
  35 #define CHILD_STACK_SIZE        10485760
  36
  37 struct run_as_data {
  38         int (*cmd)(void *data);
  39         void *data;
  40         uid_t uid;
  41         gid_t gid;
  42         int retval_pipe;
  43 };
  44
  45 struct mkdir_data {
  46         const char *path;
  47         mode_t mode;
  48 };
  49
  50 struct open_data {
  51         const char *path;
  52         int flags;
  53         mode_t mode;
  54 };
  55
  56 /*
  57  * Create recursively directory using the FULL path.
  58  */
  59 static
  60 int _mkdir_recursive(void *_data)
  61 {
  62         struct mkdir_data *data = _data;
  63         const char *path;
  64         char *p, tmp[PATH_MAX];
  65         struct stat statbuf;
  66         mode_t mode;
  67         size_t len;
  68         int ret;
  69
  70         path = data->path;
  71         mode = data->mode;
  72
  73         ret = snprintf(tmp, sizeof(tmp), "%s", path);
  74         if (ret < 0) {
  75                 PERROR("snprintf mkdir");
  76                 goto error;
  77         }
  78
  79         len = ret;
  80         if (tmp[len - 1] == '/') {
  81                 tmp[len - 1] = 0;
  82         }
  83
  84         for (p = tmp + 1; *p; p++) {
  85                 if (*p == '/') {
  86                         *p = 0;
  87                         ret = stat(tmp, &statbuf);
  88                         if (ret < 0) {
  89                                 ret = mkdir(tmp, mode);
  90                                 if (ret < 0) {
  91                                         if (!(errno == EEXIST)) {
  92                                                 PERROR("mkdir recursive");
  93                                                 ret = -errno;
  94                                                 goto error;
  95                                         }
  96                                 }
  97                         }
  98                         *p = '/';
  99                 }
 100         }
 101
 102         ret = mkdir(tmp, mode);
 103         if (ret < 0) {
 104                 if (!(errno == EEXIST)) {
 105                         PERROR("mkdir recursive last piece");
 106                         ret = -errno;
 107                 } else {
 108                         ret = 0;
 109                 }
 110         }
 111
 112 error:
 113         return ret;
 114 }
 115
 116 static
 117 int _mkdir(void *_data)
 118 {
 119         struct mkdir_data *data = _data;
 120         return mkdir(data->path, data->mode);
 121 }
 122
 123 static
 124 int _open(void *_data)
 125 {
 126         struct open_data *data = _data;
 127         return open(data->path, data->flags, data->mode);
 128 }
 129
 130 static
 131 int child_run_as(void *_data)
 132 {
 133         struct run_as_data *data = _data;
 134         size_t writelen, writeleft, index;
 135         union {
 136                 int i;
 137                 char c[sizeof(int)];
 138         } sendret;
 139         int ret;
 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                         return EXIT_FAILURE;
 153                 }
 154         }
 155         if (data->uid != geteuid()) {
 156                 ret = seteuid(data->uid);
 157                 if (ret < 0) {
 158                         perror("seteuid");
 159                         return EXIT_FAILURE;
 160                 }
 161         }
 162         /*
 163          * Also set umask to 0 for mkdir executable bit.
 164          */
 165         umask(0);
 166         sendret.i = (*data->cmd)(data->data);
 167         /* send back return value */
 168         writeleft = sizeof(sendret);
 169         index = 0;
 170         do {
 171                 writelen = write(data->retval_pipe, &sendret.c[index],
 172                                 writeleft);
 173                 if (writelen < 0) {
 174                         perror("write");
 175                         return EXIT_FAILURE;
 176                 }
 177                 writeleft -= writelen;
 178                 index += writelen;
 179         } while (writeleft > 0);
 180         return EXIT_SUCCESS;
 181 }
 182
 183 static
 184 int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 185 {
 186         struct run_as_data run_as_data;
 187         int ret = 0;
 188         int status;
 189         pid_t pid;
 190         int retval_pipe[2];
 191         ssize_t readlen, readleft, index;
 192         void *child_stack;
 193         union {
 194                 int i;
 195                 char c[sizeof(int)];
 196         } retval;
 197
 198         /*
 199          * If we are non-root, we can only deal with our own uid.
 200          */
 201         if (geteuid() != 0) {
 202                 if (uid != geteuid()) {
 203                         ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)",
 204                                 uid, geteuid());
 205                         return -EPERM;
 206                 }
 207         }
 208
 209         ret = pipe(retval_pipe);
 210         if (ret < 0) {
 211                 perror("pipe");
 212                 goto end;
 213         }
 214         run_as_data.data = data;
 215         run_as_data.cmd = cmd;
 216         run_as_data.uid = uid;
 217         run_as_data.gid = gid;
 218         run_as_data.retval_pipe = retval_pipe[1];       /* write end */
 219         child_stack = mmap(NULL, CHILD_STACK_SIZE,
 220                 PROT_WRITE | PROT_READ,
 221                 MAP_PRIVATE | MAP_GROWSDOWN | MAP_ANONYMOUS | MAP_STACK,
 222                 -1, 0);
 223         if (child_stack == MAP_FAILED) {
 224                 perror("mmap");
 225                 ret = -ENOMEM;
 226                 goto close_pipe;
 227         }
 228         /*
 229          * Pointing to the middle of the stack to support architectures
 230          * where the stack grows up (HPPA).
 231          */
 232         pid = clone(child_run_as, child_stack + (CHILD_STACK_SIZE / 2),
 233                 CLONE_FILES | SIGCHLD | CLONE_VM,
 234                 &run_as_data, NULL);
 235         if (pid < 0) {
 236                 perror("clone");
 237                 ret = pid;
 238                 goto unmap_stack;
 239         }
 240         /* receive return value */
 241         readleft = sizeof(retval);
 242         index = 0;
 243         do {
 244                 readlen = read(retval_pipe[0], &retval.c[index], readleft);
 245                 if (readlen < 0) {
 246                         perror("read");
 247                         ret = -1;
 248                         break;
 249                 }
 250                 readleft -= readlen;
 251                 index += readlen;
 252         } while (readleft > 0);
 253
 254         /*
 255          * Parent: wait for child to return, in which case the
 256          * shared memory map will have been created.
 257          */
 258         pid = waitpid(pid, &status, 0);
 259         if (pid < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
 260                 perror("wait");
 261                 ret = -1;
 262         }
 263 unmap_stack:
 264         ret = munmap(child_stack, CHILD_STACK_SIZE);
 265         if (ret < 0) {
 266                 perror("munmap");
 267         }
 268 close_pipe:
 269         close(retval_pipe[0]);
 270         close(retval_pipe[1]);
 271 end:
 272         return retval.i;
 273 }
 274
 275 int mkdir_recursive_run_as(const char *path, mode_t mode, uid_t uid, gid_t gid)
 276 {
 277         struct mkdir_data data;
 278
 279         DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d",
 280                         path, mode, uid, gid);
 281         data.path = path;
 282         data.mode = mode;
 283         return run_as(_mkdir_recursive, &data, uid, gid);
 284 }
 285
 286 int mkdir_run_as(const char *path, mode_t mode, uid_t uid, gid_t gid)
 287 {
 288         struct mkdir_data data;
 289
 290         DBG3("mkdir() %s with mode %d for uid %d and gid %d",
 291                         path, mode, uid, gid);
 292         data.path = path;
 293         data.mode = mode;
 294         return run_as(_mkdir, &data, uid, gid);
 295 }
 296
 297 /*
 298  * Note: open_run_as is currently not working. We'd need to pass the fd
 299  * opened in the child to the parent.
 300  */
 301 int open_run_as(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
 302 {
 303         struct open_data data;
 304
 305         DBG3("open() %s with flags %X mode %d for uid %d and gid %d",
 306                         path, flags, mode, uid, gid);
 307         data.path = path;
 308         data.flags = flags;
 309         data.mode = mode;
 310         return run_as(_open, &data, uid, gid);
 311 }