jail/jail.c

   1 /*
   2  * Copyright (C) 2015 John Crispin <blogic@openwrt.org>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU Lesser General Public License version 2.1
   6  * as published by the Free Software Foundation
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11  * GNU General Public License for more details.
  12  */
  13
  14 #define _GNU_SOURCE
  15 #include <sys/syscall.h>
  16 #include <sys/mman.h>
  17 #include <sys/utsname.h>
  18 #include <sys/types.h>
  19 #include <sys/syscall.h>
  20 #include <sys/types.h>
  21 #include <sys/mount.h>
  22 #include <sys/prctl.h>
  23 #include <sys/wait.h>
  24
  25 #include <stdlib.h>
  26 #include <unistd.h>
  27 #include <values.h>
  28 #include <errno.h>
  29 #include <stdio.h>
  30 #include <string.h>
  31 #include <sys/stat.h>
  32 #include <fcntl.h>
  33 #include <syslog.h>
  34 #include <libgen.h>
  35 #include <glob.h>
  36 #include <elf.h>
  37 #include <sched.h>
  38
  39 #include "elf.h"
  40
  41 #include <libubox/utils.h>
  42 #include <libubox/list.h>
  43 #include <libubox/uloop.h>
  44
  45 #define STACK_SIZE      (1024 * 1024)
  46 #define OPT_ARGS        "P:S:n:r:w:psuld"
  47
  48 struct extra {
  49         struct list_head list;
  50
  51         const char *path;
  52         const char *name;
  53         int readonly;
  54 };
  55
  56 static LIST_HEAD(extras);
  57
  58 extern int pivot_root(const char *new_root, const char *put_old);
  59
  60 int debug = 0;
  61
  62 static char child_stack[STACK_SIZE];
  63
  64 static int mkdir_p(char *dir, mode_t mask)
  65 {
  66         char *l = strrchr(dir, '/');
  67         int ret;
  68
  69         if (!l)
  70                 return 0;
  71
  72         *l = '\0';
  73
  74         if (mkdir_p(dir, mask))
  75                 return -1;
  76
  77         *l = '/';
  78
  79         ret = mkdir(dir, mask);
  80         if (ret && errno == EEXIST)
  81                 return 0;
  82
  83         if (ret)
  84                 ERROR("mkdir failed on %s: %s\n", dir, strerror(errno));
  85
  86         return ret;
  87 }
  88
  89 static int mount_bind(const char *root, const char *path, const char *name, int readonly, int error)
  90 {
  91         const char *p = path;
  92         struct stat s;
  93         char old[256];
  94         char new[256];
  95         int fd;
  96
  97         if (strstr(p, "local"))
  98                 p = "/lib";
  99
 100         snprintf(old, sizeof(old), "%s/%s", path, name);
 101         snprintf(new, sizeof(new), "%s%s", root, p);
 102
 103         mkdir_p(new, 0755);
 104
 105         snprintf(new, sizeof(new), "%s%s/%s", root, p, name);
 106
 107         if (stat(old, &s)) {
 108                 ERROR("%s does not exist\n", old);
 109                 return error;
 110         }
 111
 112         if (S_ISDIR(s.st_mode)) {
 113                 mkdir_p(new, 0755);
 114         } else {
 115                 fd = creat(new, 0644);
 116                 if (fd == -1) {
 117                         ERROR("failed to create %s: %s\n", new, strerror(errno));
 118                         return -1;
 119                 }
 120                 close(fd);
 121         }
 122
 123         if (mount(old, new, NULL, MS_BIND, NULL)) {
 124                 ERROR("failed to mount -B %s %s: %s\n", old, new, strerror(errno));
 125                 return -1;
 126         }
 127
 128         if (readonly && mount(old, new, NULL, MS_BIND | MS_REMOUNT | MS_RDONLY, NULL)) {
 129                 ERROR("failed to remount ro %s: %s\n", new, strerror(errno));
 130                 return -1;
 131         }
 132
 133         DEBUG("mount -B %s %s\n", old, new);
 134
 135         return 0;
 136 }
 137
 138 static int build_jail(const char *path)
 139 {
 140         struct library *l;
 141         struct extra *m;
 142         int ret = 0;
 143
 144         mkdir(path, 0755);
 145
 146         if (mount("tmpfs", path, "tmpfs", MS_NOATIME, "mode=0744")) {
 147                 ERROR("tmpfs mount failed %s\n", strerror(errno));
 148                 return -1;
 149         }
 150
 151         avl_for_each_element(&libraries, l, avl)
 152                 if (mount_bind(path, l->path, l->name, 1, -1))
 153                         return -1;
 154
 155         list_for_each_entry(m, &extras, list)
 156                 if (mount_bind(path, m->path, m->name, m->readonly, 0))
 157                         return -1;
 158
 159         return ret;
 160 }
 161
 162 static void _umount(const char *root, const char *path)
 163 {
 164         char *buf = NULL;
 165
 166         if (asprintf(&buf, "%s%s", root, path) < 0) {
 167                 ERROR("failed to alloc umount buffer: %s\n", strerror(errno));
 168         } else {
 169                 DEBUG("umount %s\n", buf);
 170                 umount(buf);
 171                 free(buf);
 172         }
 173 }
 174
 175 static int stop_jail(const char *root)
 176 {
 177         struct library *l;
 178         struct extra *m;
 179
 180         avl_for_each_element(&libraries, l, avl) {
 181                 char path[256];
 182                 char *p = l->path;
 183
 184                 if (strstr(p, "local"))
 185                         p = "/lib";
 186
 187                 snprintf(path, sizeof(path), "%s%s/%s", root, p, l->name);
 188                 DEBUG("umount %s\n", path);
 189                 umount(path);
 190         }
 191
 192         list_for_each_entry(m, &extras, list) {
 193                 char path[256];
 194
 195                 snprintf(path, sizeof(path), "%s%s/%s", root, m->path, m->name);
 196                 DEBUG("umount %s\n", path);
 197                 umount(path);
 198         }
 199
 200         _umount(root, "/proc");
 201         _umount(root, "/sys");
 202
 203         DEBUG("umount %s\n", root);
 204         umount(root);
 205         rmdir(root);
 206
 207         return 0;
 208 }
 209
 210 #define MAX_ENVP        8
 211 static char** build_envp(const char *seccomp, int debug)
 212 {
 213         static char *envp[MAX_ENVP];
 214         static char preload_var[64];
 215         static char seccomp_var[64];
 216         static char debug_var[] = "LD_DEBUG=all";
 217         char *preload_lib = find_lib("libpreload-seccomp.so");
 218         int count = 0;
 219
 220         if (seccomp && !preload_lib) {
 221                 ERROR("failed to add preload-lib to env\n");
 222                 return NULL;
 223         }
 224         if (seccomp) {
 225                 snprintf(seccomp_var, sizeof(seccomp_var), "SECCOMP_FILE=%s", seccomp);
 226                 envp[count++] = seccomp_var;
 227                 snprintf(preload_var, sizeof(preload_var), "LD_PRELOAD=%s", preload_lib);
 228                 envp[count++] = preload_var;
 229         }
 230         if (debug)
 231                 envp[count++] = debug_var;
 232
 233         return envp;
 234 }
 235
 236 static int spawn(const char *path, char **argv, const char *seccomp)
 237 {
 238         pid_t pid = fork();
 239
 240         if (pid < 0) {
 241                 ERROR("failed to spawn %s: %s\n", *argv, strerror(errno));
 242                 return -1;
 243         } else if (!pid) {
 244                 char **envp = build_envp(seccomp, 0);
 245
 246                 INFO("spawning %s\n", *argv);
 247                 execve(*argv, argv, envp);
 248                 ERROR("failed to spawn child %s: %s\n", *argv, strerror(errno));
 249                 exit(-1);
 250         }
 251
 252         return pid;
 253 }
 254
 255 static int usage(void)
 256 {
 257         fprintf(stderr, "jail <options> -D <binary> <params ...>\n");
 258         fprintf(stderr, "  -P <path>\tpath where the jail will be staged\n");
 259         fprintf(stderr, "  -S <file>\tseccomp filter\n");
 260         fprintf(stderr, "  -n <name>\tthe name of the jail\n");
 261         fprintf(stderr, "  -r <file>\treadonly files that should be staged\n");
 262         fprintf(stderr, "  -w <file>\twriteable files that should be staged\n");
 263         fprintf(stderr, "  -p\t\tjail has /proc\t\n");
 264         fprintf(stderr, "  -s\t\tjail has /sys\t\n");
 265         fprintf(stderr, "  -l\t\tjail has /dev/log\t\n");
 266         fprintf(stderr, "  -u\t\tjail has a ubus socket\t\n");
 267
 268         return -1;
 269 }
 270
 271 static int child_running = 1;
 272
 273 static void child_process_handler(struct uloop_process *c, int ret)
 274 {
 275         INFO("child (%d) exited: %d\n", c->pid, ret);
 276         uloop_end();
 277         child_running = 0;
 278 }
 279
 280 struct uloop_process child_process = {
 281         .cb = child_process_handler,
 282 };
 283
 284 static int spawn_child(void *arg)
 285 {
 286         char *path = get_current_dir_name();
 287         int procfs = 0, sysfs = 0;
 288         char *seccomp = NULL;
 289         char **argv = arg;
 290         int argc = 0, ch;
 291         char *mpoint;
 292
 293         while (argv[argc])
 294                 argc++;
 295
 296         optind = 0;
 297         while ((ch = getopt(argc, argv, OPT_ARGS)) != -1) {
 298                 switch (ch) {
 299                 case 'd':
 300                         debug = 1;
 301                         break;
 302                 case 'S':
 303                         seccomp = optarg;
 304                         break;
 305                 case 'p':
 306                         procfs = 1;
 307                         break;
 308                 case 's':
 309                         sysfs = 1;
 310                         break;
 311                 case 'n':
 312                         sethostname(optarg, strlen(optarg));
 313                         break;
 314                 }
 315         }
 316
 317         asprintf(&mpoint, "%s/old", path);
 318         mkdir_p(mpoint, 0755);
 319         if (pivot_root(path, mpoint) == -1) {
 320                 ERROR("pivot_root failed:%s\n", strerror(errno));
 321                 return -1;
 322         }
 323         free(mpoint);
 324         umount2("/old", MNT_DETACH);
 325         rmdir("/old");
 326         if (procfs) {
 327                 mkdir("/proc", 0755);
 328                 mount("proc", "/proc", "proc", MS_NOATIME, 0);
 329         }
 330         if (sysfs) {
 331                 mkdir("/sys", 0755);
 332                 mount("sysfs", "/sys", "sysfs", MS_NOATIME, 0);
 333         }
 334         mount(NULL, "/", NULL, MS_RDONLY | MS_REMOUNT, 0);
 335
 336         uloop_init();
 337
 338         child_process.pid = spawn(path, &argv[optind], seccomp);
 339         uloop_process_add(&child_process);
 340         uloop_run();
 341         uloop_done();
 342         if (child_running) {
 343                 kill(child_process.pid, SIGTERM);
 344                 waitpid(child_process.pid, NULL, 0);
 345         }
 346
 347         return 0;
 348 }
 349
 350 static int namespace_running = 1;
 351
 352 static void namespace_process_handler(struct uloop_process *c, int ret)
 353 {
 354         INFO("namespace (%d) exited: %d\n", c->pid, ret);
 355         uloop_end();
 356         namespace_running = 0;
 357 }
 358
 359 struct uloop_process namespace_process = {
 360         .cb = namespace_process_handler,
 361 };
 362
 363 static void spawn_namespace(const char *path, int argc, char **argv)
 364 {
 365         char *dir = get_current_dir_name();
 366
 367         uloop_init();
 368         chdir(path);
 369         namespace_process.pid = clone(spawn_child,
 370                         child_stack + STACK_SIZE,
 371                         CLONE_NEWUTS | CLONE_NEWPID | CLONE_NEWNS | SIGCHLD, argv);
 372
 373         if (namespace_process.pid != -1) {
 374                 chdir(dir);
 375                 free(dir);
 376                 uloop_process_add(&namespace_process);
 377                 uloop_run();
 378                 uloop_done();
 379                 if (namespace_running) {
 380                         kill(namespace_process.pid, SIGTERM);
 381                         waitpid(namespace_process.pid, NULL, 0);
 382                 }
 383         } else {
 384                 ERROR("failed to spawn namespace: %s\n", strerror(errno));
 385         }
 386 }
 387
 388 static void add_extra(char *name, int readonly)
 389 {
 390         struct extra *f;
 391
 392         if (*name != '/') {
 393                 ERROR("%s is not an absolute path\n", name);
 394                 return;
 395         }
 396
 397         f = calloc(1, sizeof(struct extra));
 398
 399         f->name = basename(name);
 400         f->path = dirname(strdup(name));
 401         f->readonly = readonly;
 402
 403         list_add_tail(&f->list, &extras);
 404 }
 405
 406 int main(int argc, char **argv)
 407 {
 408         uid_t uid = getuid();
 409         const char *name = NULL;
 410         char *path = NULL;
 411         struct stat s;
 412         int ch, ret;
 413         char log[] = "/dev/log";
 414         char ubus[] = "/var/run/ubus.sock";
 415
 416         if (uid) {
 417                 ERROR("not root, aborting: %s\n", strerror(errno));
 418                 return -1;
 419         }
 420
 421         umask(022);
 422
 423         while ((ch = getopt(argc, argv, OPT_ARGS)) != -1) {
 424                 switch (ch) {
 425                 case 'd':
 426                         debug = 1;
 427                         break;
 428                 case 'P':
 429                         path = optarg;
 430                         break;
 431                 case 'n':
 432                         name = optarg;
 433                         break;
 434                 case 'S':
 435                 case 'r':
 436                         add_extra(optarg, 1);
 437                         break;
 438                 case 'w':
 439                         add_extra(optarg, 0);
 440                         break;
 441                 case 'u':
 442                         add_extra(ubus, 0);
 443                         break;
 444                 case 'l':
 445                         add_extra(log, 0);
 446                         break;
 447                 }
 448         }
 449
 450         if (argc - optind < 1)
 451                 return usage();
 452
 453         if (!path && asprintf(&path, "/tmp/%s", basename(argv[optind])) == -1) {
 454                 ERROR("failed to set root path\n: %s", strerror(errno));
 455                 return -1;
 456         }
 457
 458         if (!stat(path, &s)) {
 459                 ERROR("%s already exists: %s\n", path, strerror(errno));
 460                 return -1;
 461         }
 462
 463         if (name)
 464                 prctl(PR_SET_NAME, name, NULL, NULL, NULL);
 465
 466         avl_init(&libraries, avl_strcmp, false, NULL);
 467         alloc_library_path("/lib64");
 468         alloc_library_path("/lib");
 469         alloc_library_path("/usr/lib");
 470         load_ldso_conf("/etc/ld.so.conf");
 471
 472         if (elf_load_deps(argv[optind])) {
 473                 ERROR("failed to load dependencies\n");
 474                 return -1;
 475         }
 476
 477         if (elf_load_deps("libpreload-seccomp.so")) {
 478                 ERROR("failed to load libpreload-seccomp.so\n");
 479                 return -1;
 480         }
 481
 482         ret = build_jail(path);
 483
 484         if (!ret)
 485                 spawn_namespace(path, argc, argv);
 486         else
 487                 ERROR("failed to build jail\n");
 488
 489         stop_jail(path);
 490
 491         return ret;
 492 }