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 __FreeBSD__
  42 # ifndef MAP_STACK
  43 #  define MAP_STACK             0
  44 # endif
  45 #else   /* FreeBSD MAP_STACK always return -ENOMEM */
  46 # define MAP_STACK              0
  47 #endif
  48
  49 #ifndef MAP_GROWSDOWN
  50 #define MAP_GROWSDOWN           0
  51 #endif
  52
  53 #ifndef MAP_ANONYMOUS
  54 #define MAP_ANONYMOUS           MAP_ANON
  55 #endif
  56
  57 struct run_as_data {
  58         int (*cmd)(void *data);
  59         void *data;
  60         uid_t uid;
  61         gid_t gid;
  62         int retval_pipe;
  63 };
  64
  65 struct run_as_mkdir_data {
  66         const char *path;
  67         mode_t mode;
  68 };
  69
  70 struct run_as_open_data {
  71         const char *path;
  72         int flags;
  73         mode_t mode;
  74 };
  75
  76 /*
  77  * Create recursively directory using the FULL path.
  78  */
  79 static
  80 int _mkdir_recursive(void *_data)
  81 {
  82         struct run_as_mkdir_data *data = _data;
  83         const char *path;
  84         char *p, tmp[PATH_MAX];
  85         struct stat statbuf;
  86         mode_t mode;
  87         size_t len;
  88         int ret;
  89
  90         path = data->path;
  91         mode = data->mode;
  92
  93         ret = snprintf(tmp, sizeof(tmp), "%s", path);
  94         if (ret < 0) {
  95                 PERROR("snprintf mkdir");
  96                 goto error;
  97         }
  98
  99         len = ret;
 100         if (tmp[len - 1] == '/') {
 101                 tmp[len - 1] = 0;
 102         }
 103
 104         for (p = tmp + 1; *p; p++) {
 105                 if (*p == '/') {
 106                         *p = 0;
 107                         ret = stat(tmp, &statbuf);
 108                         if (ret < 0) {
 109                                 ret = mkdir(tmp, mode);
 110                                 if (ret < 0) {
 111                                         if (!(errno == EEXIST)) {
 112                                                 PERROR("mkdir recursive");
 113                                                 ret = -errno;
 114                                                 goto error;
 115                                         }
 116                                 }
 117                         }
 118                         *p = '/';
 119                 }
 120         }
 121
 122         ret = mkdir(tmp, mode);
 123         if (ret < 0) {
 124                 if (!(errno == EEXIST)) {
 125                         PERROR("mkdir recursive last piece");
 126                         ret = -errno;
 127                 } else {
 128                         ret = 0;
 129                 }
 130         }
 131
 132 error:
 133         return ret;
 134 }
 135
 136 static
 137 int _mkdir(void *_data)
 138 {
 139         struct run_as_mkdir_data *data = _data;
 140         return mkdir(data->path, data->mode);
 141 }
 142
 143 static
 144 int _open(void *_data)
 145 {
 146         struct run_as_open_data *data = _data;
 147         return open(data->path, data->flags, data->mode);
 148 }
 149
 150 static
 151 int child_run_as(void *_data)
 152 {
 153         struct run_as_data *data = _data;
 154         size_t writelen, writeleft, index;
 155         union {
 156                 int i;
 157                 char c[sizeof(int)];
 158         } sendret;
 159         int ret;
 160
 161         /*
 162          * Child: it is safe to drop egid and euid while sharing the
 163          * file descriptors with the parent process, since we do not
 164          * drop "uid": therefore, the user we are dropping egid/euid to
 165          * cannot attach to this process with, e.g. ptrace, nor map this
 166          * process memory.
 167          */
 168         if (data->gid != getegid()) {
 169                 ret = setegid(data->gid);
 170                 if (ret < 0) {
 171                         perror("setegid");
 172                         return EXIT_FAILURE;
 173                 }
 174         }
 175         if (data->uid != geteuid()) {
 176                 ret = seteuid(data->uid);
 177                 if (ret < 0) {
 178                         perror("seteuid");
 179                         return EXIT_FAILURE;
 180                 }
 181         }
 182         /*
 183          * Also set umask to 0 for mkdir executable bit.
 184          */
 185         umask(0);
 186         sendret.i = (*data->cmd)(data->data);
 187         /* send back return value */
 188         writeleft = sizeof(sendret);
 189         index = 0;
 190         do {
 191                 writelen = write(data->retval_pipe, &sendret.c[index],
 192                                 writeleft);
 193                 if (writelen < 0) {
 194                         perror("write");
 195                         return EXIT_FAILURE;
 196                 }
 197                 writeleft -= writelen;
 198                 index += writelen;
 199         } while (writeleft > 0);
 200         return EXIT_SUCCESS;
 201 }
 202
 203 static
 204 int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
 205 {
 206         struct run_as_data run_as_data;
 207         int ret = 0;
 208         int status;
 209         pid_t pid;
 210         int retval_pipe[2];
 211         ssize_t readlen, readleft, index;
 212         void *child_stack;
 213         union {
 214                 int i;
 215                 char c[sizeof(int)];
 216         } retval;
 217
 218         /*
 219          * If we are non-root, we can only deal with our own uid.
 220          */
 221         if (geteuid() != 0) {
 222                 if (uid != geteuid()) {
 223                         ERR("Client (%d)/Server (%d) UID mismatch (and sessiond is not root)",
 224                                 uid, geteuid());
 225                         return -EPERM;
 226                 }
 227         }
 228
 229         ret = pipe(retval_pipe);
 230         if (ret < 0) {
 231                 perror("pipe");
 232                 retval.i = ret;
 233                 goto end;
 234         }
 235         run_as_data.data = data;
 236         run_as_data.cmd = cmd;
 237         run_as_data.uid = uid;
 238         run_as_data.gid = gid;
 239         run_as_data.retval_pipe = retval_pipe[1];       /* write end */
 240         child_stack = mmap(NULL, RUNAS_CHILD_STACK_SIZE,
 241                 PROT_WRITE | PROT_READ,
 242                 MAP_PRIVATE | MAP_GROWSDOWN | MAP_ANONYMOUS | MAP_STACK,
 243                 -1, 0);
 244         if (child_stack == MAP_FAILED) {
 245                 perror("mmap");
 246                 retval.i = -ENOMEM;
 247                 goto close_pipe;
 248         }
 249         /*
 250          * Pointing to the middle of the stack to support architectures
 251          * where the stack grows up (HPPA).
 252          */
 253         pid = lttng_clone_files(child_run_as, child_stack + (RUNAS_CHILD_STACK_SIZE / 2),
 254                 &run_as_data);
 255         if (pid < 0) {
 256                 perror("clone");
 257                 retval.i = pid;
 258                 goto unmap_stack;
 259         }
 260         /* receive return value */
 261         readleft = sizeof(retval);
 262         index = 0;
 263         do {
 264                 readlen = read(retval_pipe[0], &retval.c[index], readleft);
 265                 if (readlen < 0) {
 266                         perror("read");
 267                         ret = -1;
 268                         break;
 269                 }
 270                 readleft -= readlen;
 271                 index += readlen;
 272         } while (readleft > 0);
 273
 274         /*
 275          * Parent: wait for child to return, in which case the
 276          * shared memory map will have been created.
 277          */
 278         pid = waitpid(pid, &status, 0);
 279         if (pid < 0 || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
 280                 perror("wait");
 281                 retval.i = -1;
 282         }
 283 unmap_stack:
 284         ret = munmap(child_stack, RUNAS_CHILD_STACK_SIZE);
 285         if (ret < 0) {
 286                 perror("munmap");
 287                 retval.i = ret;
 288         }
 289 close_pipe:
 290         close(retval_pipe[0]);
 291         close(retval_pipe[1]);
 292 end:
 293         return retval.i;
 294 }
 295
 296 int run_as_mkdir_recursive(const char *path, mode_t mode, uid_t uid, gid_t gid)
 297 {
 298         struct run_as_mkdir_data data;
 299
 300         DBG3("mkdir() recursive %s with mode %d for uid %d and gid %d",
 301                         path, mode, uid, gid);
 302         data.path = path;
 303         data.mode = mode;
 304         return run_as(_mkdir_recursive, &data, uid, gid);
 305 }
 306
 307 int run_as_mkdir(const char *path, mode_t mode, uid_t uid, gid_t gid)
 308 {
 309         struct run_as_mkdir_data data;
 310
 311         DBG3("mkdir() %s with mode %d for uid %d and gid %d",
 312                         path, mode, uid, gid);
 313         data.path = path;
 314         data.mode = mode;
 315         return run_as(_mkdir, &data, uid, gid);
 316 }
 317
 318 /*
 319  * Note: open_run_as is currently not working. We'd need to pass the fd
 320  * opened in the child to the parent.
 321  */
 322 int run_as_open(const char *path, int flags, mode_t mode, uid_t uid, gid_t gid)
 323 {
 324         struct run_as_open_data data;
 325
 326         DBG3("open() %s with flags %X mode %d for uid %d and gid %d",
 327                         path, flags, mode, uid, gid);
 328         data.path = path;
 329         data.flags = flags;
 330         data.mode = mode;
 331         return run_as(_open, &data, uid, gid);
 332 }