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