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 #include "runas.h"
  36
  37 #define RUNAS_CHILD_STACK_SIZE  10485760
  38
  39 struct run_as_data {
  40         int (*cmd)(void *data);
  41         void *data;
  42         uid_t uid;
  43         gid_t gid;
  44         int retval_pipe;
  45 };
  46
  47 struct run_as_mkdir_data {
  48         const char *path;
  49         mode_t mode;
  50 };
  51
  52 struct run_as_open_data {
  53         const char *path;
  54         int flags;
  55         mode_t mode;
  56 };
  57
  58 /*
  59  * Create recursively directory using the FULL path.
  60  */
  61 static
  62 int _mkdir_recursive(void *_data)
  63 {
  64         struct run_as_mkdir_data *data = _data;
  65         const char *path;
  66         char *p, tmp[PATH_MAX];
  67         struct stat statbuf;
  68         mode_t mode;
  69         size_t len;
  70         int ret;
  71
  72         path = data->path;
  73         mode = data->mode;
  74
  75         ret = snprintf(tmp, sizeof(tmp), "%s", path);
  76         if (ret < 0) {
  77                 PERROR("snprintf mkdir");
  78                 goto error;
  79         }
  80
  81         len = ret;
  82         if (tmp[len - 1] == '/') {
  83                 tmp[len - 1] = 0;
  84         }
  85
  86         for (p = tmp + 1; *p; p++) {
  87                 if (*p == '/') {
  88                         *p = 0;
  89                         ret = stat(tmp, &statbuf);
  90                         if (ret < 0) {
  91                                 ret = mkdir(tmp, mode);
  92                                 if (ret < 0) {
  93                                         if (!(errno == EEXIST)) {
  94                                                 PERROR("mkdir recursive");
  95                                                 ret = -errno;
  96                                                 goto error;
  97                                         }
  98                                 }
  99                         }
 100                         *p = '/';
 101                 }
 102         }
 103
 104         ret = mkdir(tmp, mode);
 105         if (ret < 0) {
 106                 if (!(errno == EEXIST)) {
 107                         PERROR("mkdir recursive last piece");
 108                         ret = -errno;
 109                 } else {
 110                         ret = 0;
 111                 }
 112         }
 113
 114 error:
 115         return ret;
 116 }
 117
 118 static
 119 int _mkdir(void *_data)
 120 {
 121         struct run_as_mkdir_data *data = _data;
 122         return mkdir(data->path, data->mode);
 123 }
 124
 125 static
 126 int _open(void *_data)
 127 {
 128         struct run_as_open_data *data = _data;
 129         return open(data->path, data->flags, data->mode);
 130 }
 131
 132 static
 133 int child_run_as(void *_data)
 134 {
 135         struct run_as_data *data = _data;
 136         size_t writelen, writeleft, index;
 137         union {
 138                 int i;
 139                 char c[sizeof(int)];
 140         } sendret;
 141         int ret;
 142
 143         /*
 144          * Child: it is safe to drop egid and euid while sharing the
 145          * file descriptors with the parent process, since we do not
 146          * drop "uid": therefore, the user we are dropping egid/euid to
 147          * cannot attach to this process with, e.g. ptrace, nor map this
 148          * process memory.
 149          */
 150         if (data->gid != getegid()) {
 151                 ret = setegid(data->gid);
 152                 if (ret < 0) {
 153                         perror("setegid");
 154                         return EXIT_FAILURE;
 155                 }
 156         }
 157         if (data->uid != geteuid()) {
 158                 ret = seteuid(data->uid);
 159                 if (ret < 0) {
 160                         perror("seteuid");
 161                         return EXIT_FAILURE;
 162                 }
 163         }
 164         /*
 165          * Also set umask to 0 for mkdir executable bit.
 166          */
 167         umask(0);
 168         sendret.i = (*data->cmd)(data->data);
 169         /* send back return value */
 170         writeleft = sizeof(sendret);
 171         index = 0;
 172         do {
 173                 writelen = write(data->retval_pipe, &sendret.c[index],
 174                                 writeleft);
 175                 if (writelen < 0) {
 176                         perror("write");
 177                         return EXIT_FAILURE;
 178                 }
 179                 writeleft -= writelen;
 180                 index += writelen;
 181         } while (writeleft > 0);
 182         return EXIT_SUCCESS;
 183 }
 184
 185 static
 186 int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 187 {
 188         struct run_as_data run_as_data;
 189         int ret = 0;
 190         int status;
 191         pid_t pid;
 192         int retval_pipe[2];
 193         ssize_t readlen, readleft, index;
 194         void *child_stack;
 195         union {
 196                 int i;
 197                 char c[sizeof(int)];
 198         } retval;
 199
 200         /*
 201          * If we are non-root, we can only deal with our own uid.
 202          */
 203         if (geteuid() != 0) {
 204                 if (uid != geteuid()) {
 205                         ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)",
 206                                 uid, geteuid());
 207                         return -EPERM;
 208                 }
 209         }
 210
 211         ret = pipe(retval_pipe);
 212         if (ret < 0) {
 213                 perror("pipe");
 214                 goto end;
 215         }
 216         run_as_data.data = data;
 217         run_as_data.cmd = cmd;
 218         run_as_data.uid = uid;
 219         run_as_data.gid = gid;
 220         run_as_data.retval_pipe = retval_pipe[1];       /* write end */
 221         child_stack = mmap(NULL, RUNAS_CHILD_STACK_SIZE,
 222                 PROT_WRITE | PROT_READ,
 223                 MAP_PRIVATE | MAP_GROWSDOWN | MAP_ANONYMOUS | MAP_STACK,
 224                 -1, 0);
 225         if (child_stack == MAP_FAILED) {
 226                 perror("mmap");
 227                 ret = -ENOMEM;
 228                 goto close_pipe;
 229         }
 230         /*
 231          * Pointing to the middle of the stack to support architectures
 232          * where the stack grows up (HPPA).
 233          */
 234         pid = clone(child_run_as, child_stack + (RUNAS_CHILD_STACK_SIZE / 2),
 235                 CLONE_FILES | SIGCHLD,
 236                 &run_as_data, NULL);
 237         if (pid < 0) {
 238                 perror("clone");
 239                 ret = pid;
 240                 goto unmap_stack;
 241         }
 242         /* receive return value */
 243         readleft = sizeof(retval);
 244         index = 0;
 245         do {
 246                 readlen = read(retval_pipe[0], &retval.c[index], readleft);
 247                 if (readlen < 0) {
 248                         perror("read");
 249                         ret = -1;
 250                         break;
 251                 }
 252                 readleft -= readlen;
 253                 index += readlen;
 254         } while (readleft > 0);
 255
 256         /*
 257          * Parent: wait for child to return, in which case the
 258          * shared memory map will have been created.
 259          */
 260         pid = waitpid(pid, &status, 0);
 261         if (pid < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
 262                 perror("wait");
 263                 ret = -1;
 264         }
 265 unmap_stack:
 266         ret = munmap(child_stack, RUNAS_CHILD_STACK_SIZE);
 267         if (ret < 0) {
 268                 perror("munmap");
 269         }
 270 close_pipe:
 271         close(retval_pipe[0]);
 272         close(retval_pipe[1]);
 273 end:
 274         return retval.i;
 275 }
 276
 277 int run_as_mkdir_recursive(const char *path, mode_t mode, uid_t uid, gid_t gid)
 278 {
 279         struct run_as_mkdir_data data;
 280
 281         DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d",
 282                         path, mode, uid, gid);
 283         data.path = path;
 284         data.mode = mode;
 285         return run_as(_mkdir_recursive, &data, uid, gid);
 286 }
 287
 288 int run_as_mkdir(const char *path, mode_t mode, uid_t uid, gid_t gid)
 289 {
 290         struct run_as_mkdir_data data;
 291
 292         DBG3("mkdir() %s with mode %d for uid %d and gid %d",
 293                         path, mode, uid, gid);
 294         data.path = path;
 295         data.mode = mode;
 296         return run_as(_mkdir, &data, uid, gid);
 297 }
 298
 299 /*
 300  * Note: open_run_as is currently not working. We'd need to pass the fd
 301  * opened in the child to the parent.
 302  */
 303 int run_as_open(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
 304 {
 305         struct run_as_open_data data;
 306
 307         DBG3("open() %s with flags %X mode %d for uid %d and gid %d",
 308                         path, flags, mode, uid, gid);
 309         data.path = path;
 310         data.flags = flags;
 311         data.mode = mode;
 312         return run_as(_open, &data, uid, gid);
 313 }