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