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 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 <common/error.h>
  34
  35 #include "runas.h"
  36
  37 #define RUNAS_CHILD_STACK_SIZE  10485760
  38
  39 #ifndef MAP_STACK
  40 #define MAP_STACK               0
  41 #endif
  42
  43 struct run_as_data {
  44         int (*cmd)(void *data);
  45         void *data;
  46         uid_t uid;
  47         gid_t gid;
  48         int retval_pipe;
  49 };
  50
  51 struct run_as_mkdir_data {
  52         const char *path;
  53         mode_t mode;
  54 };
  55
  56 struct run_as_open_data {
  57         const char *path;
  58         int flags;
  59         mode_t mode;
  60 };
  61
  62 /*
  63  * Create recursively directory using the FULL path.
  64  */
  65 static
  66 int _mkdir_recursive(void *_data)
  67 {
  68         struct run_as_mkdir_data *data = _data;
  69         const char *path;
  70         char *p, tmp[PATH_MAX];
  71         struct stat statbuf;
  72         mode_t mode;
  73         size_t len;
  74         int ret;
  75
  76         path = data->path;
  77         mode = data->mode;
  78
  79         ret = snprintf(tmp, sizeof(tmp), "%s", path);
  80         if (ret < 0) {
  81                 PERROR("snprintf mkdir");
  82                 goto error;
  83         }
  84
  85         len = ret;
  86         if (tmp[len - 1] == '/') {
  87                 tmp[len - 1] = 0;
  88         }
  89
  90         for (p = tmp + 1; *p; p++) {
  91                 if (*p == '/') {
  92                         *p = 0;
  93                         ret = stat(tmp, &statbuf);
  94                         if (ret < 0) {
  95                                 ret = mkdir(tmp, mode);
  96                                 if (ret < 0) {
  97                                         if (!(errno == EEXIST)) {
  98                                                 PERROR("mkdir recursive");
  99                                                 ret = -errno;
 100                                                 goto error;
 101                                         }
 102                                 }
 103                         }
 104                         *p = '/';
 105                 }
 106         }
 107
 108         ret = mkdir(tmp, mode);
 109         if (ret < 0) {
 110                 if (!(errno == EEXIST)) {
 111                         PERROR("mkdir recursive last piece");
 112                         ret = -errno;
 113                 } else {
 114                         ret = 0;
 115                 }
 116         }
 117
 118 error:
 119         return ret;
 120 }
 121
 122 static
 123 int _mkdir(void *_data)
 124 {
 125         struct run_as_mkdir_data *data = _data;
 126         return mkdir(data->path, data->mode);
 127 }
 128
 129 static
 130 int _open(void *_data)
 131 {
 132         struct run_as_open_data *data = _data;
 133         return open(data->path, data->flags, data->mode);
 134 }
 135
 136 static
 137 int child_run_as(void *_data)
 138 {
 139         struct run_as_data *data = _data;
 140         size_t writelen, writeleft, index;
 141         union {
 142                 int i;
 143                 char c[sizeof(int)];
 144         } sendret;
 145         int ret;
 146
 147         /*
 148          * Child: it is safe to drop egid and euid while sharing the
 149          * file descriptors with the parent process, since we do not
 150          * drop "uid": therefore, the user we are dropping egid/euid to
 151          * cannot attach to this process with, e.g. ptrace, nor map this
 152          * process memory.
 153          */
 154         if (data->gid != getegid()) {
 155                 ret = setegid(data->gid);
 156                 if (ret < 0) {
 157                         perror("setegid");
 158                         return EXIT_FAILURE;
 159                 }
 160         }
 161         if (data->uid != geteuid()) {
 162                 ret = seteuid(data->uid);
 163                 if (ret < 0) {
 164                         perror("seteuid");
 165                         return EXIT_FAILURE;
 166                 }
 167         }
 168         /*
 169          * Also set umask to 0 for mkdir executable bit.
 170          */
 171         umask(0);
 172         sendret.i = (*data->cmd)(data->data);
 173         /* send back return value */
 174         writeleft = sizeof(sendret);
 175         index = 0;
 176         do {
 177                 writelen = write(data->retval_pipe, &sendret.c[index],
 178                                 writeleft);
 179                 if (writelen < 0) {
 180                         perror("write");
 181                         return EXIT_FAILURE;
 182                 }
 183                 writeleft -= writelen;
 184                 index += writelen;
 185         } while (writeleft > 0);
 186         return EXIT_SUCCESS;
 187 }
 188
 189 static
 190 int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 191 {
 192         struct run_as_data run_as_data;
 193         int ret = 0;
 194         int status;
 195         pid_t pid;
 196         int retval_pipe[2];
 197         ssize_t readlen, readleft, index;
 198         void *child_stack;
 199         union {
 200                 int i;
 201                 char c[sizeof(int)];
 202         } retval;
 203
 204         /*
 205          * If we are non-root, we can only deal with our own uid.
 206          */
 207         if (geteuid() != 0) {
 208                 if (uid != geteuid()) {
 209                         ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)",
 210                                 uid, geteuid());
 211                         return -EPERM;
 212                 }
 213         }
 214
 215         ret = pipe(retval_pipe);
 216         if (ret < 0) {
 217                 perror("pipe");
 218                 goto end;
 219         }
 220         run_as_data.data = data;
 221         run_as_data.cmd = cmd;
 222         run_as_data.uid = uid;
 223         run_as_data.gid = gid;
 224         run_as_data.retval_pipe = retval_pipe[1];       /* write end */
 225         child_stack = mmap(NULL, RUNAS_CHILD_STACK_SIZE,
 226                 PROT_WRITE | PROT_READ,
 227                 MAP_PRIVATE | MAP_GROWSDOWN | MAP_ANONYMOUS | MAP_STACK,
 228                 -1, 0);
 229         if (child_stack == MAP_FAILED) {
 230                 perror("mmap");
 231                 ret = -ENOMEM;
 232                 goto close_pipe;
 233         }
 234         /*
 235          * Pointing to the middle of the stack to support architectures
 236          * where the stack grows up (HPPA).
 237          */
 238         pid = clone(child_run_as, child_stack + (RUNAS_CHILD_STACK_SIZE / 2),
 239                 CLONE_FILES | SIGCHLD,
 240                 &run_as_data, NULL);
 241         if (pid < 0) {
 242                 perror("clone");
 243                 ret = pid;
 244                 goto unmap_stack;
 245         }
 246         /* receive return value */
 247         readleft = sizeof(retval);
 248         index = 0;
 249         do {
 250                 readlen = read(retval_pipe[0], &retval.c[index], readleft);
 251                 if (readlen < 0) {
 252                         perror("read");
 253                         ret = -1;
 254                         break;
 255                 }
 256                 readleft -= readlen;
 257                 index += readlen;
 258         } while (readleft > 0);
 259
 260         /*
 261          * Parent: wait for child to return, in which case the
 262          * shared memory map will have been created.
 263          */
 264         pid = waitpid(pid, &status, 0);
 265         if (pid < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
 266                 perror("wait");
 267                 ret = -1;
 268         }
 269 unmap_stack:
 270         ret = munmap(child_stack, RUNAS_CHILD_STACK_SIZE);
 271         if (ret < 0) {
 272                 perror("munmap");
 273         }
 274 close_pipe:
 275         close(retval_pipe[0]);
 276         close(retval_pipe[1]);
 277 end:
 278         return retval.i;
 279 }
 280
 281 int run_as_mkdir_recursive(const char *path, mode_t mode, uid_t uid, gid_t gid)
 282 {
 283         struct run_as_mkdir_data data;
 284
 285         DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d",
 286                         path, mode, uid, gid);
 287         data.path = path;
 288         data.mode = mode;
 289         return run_as(_mkdir_recursive, &data, uid, gid);
 290 }
 291
 292 int run_as_mkdir(const char *path, mode_t mode, uid_t uid, gid_t gid)
 293 {
 294         struct run_as_mkdir_data data;
 295
 296         DBG3("mkdir() %s with mode %d for uid %d and gid %d",
 297                         path, mode, uid, gid);
 298         data.path = path;
 299         data.mode = mode;
 300         return run_as(_mkdir, &data, uid, gid);
 301 }
 302
 303 /*
 304  * Note: open_run_as is currently not working. We'd need to pass the fd
 305  * opened in the child to the parent.
 306  */
 307 int run_as_open(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
 308 {
 309         struct run_as_open_data data;
 310
 311         DBG3("open() %s with flags %X mode %d for uid %d and gid %d",
 312                         path, flags, mode, uid, gid);
 313         data.path = path;
 314         data.flags = flags;
 315         data.mode = mode;
 316         return run_as(_open, &data, uid, gid);
 317 }