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/mount.h>
  16 #include <sys/prctl.h>
  17 #include <sys/wait.h>
  18
  19 #include <stdlib.h>
  20 #include <unistd.h>
  21 #include <values.h>
  22 #include <errno.h>
  23 #include <stdio.h>
  24 #include <string.h>
  25 #include <sys/stat.h>
  26 #include <fcntl.h>
  27 #include <libgen.h>
  28 #include <sched.h>
  29
  30 #include "elf.h"
  31 #include "capabilities.h"
  32
  33 #include <libubox/list.h>
  34 #include <libubox/uloop.h>
  35
  36 #define STACK_SIZE      (1024 * 1024)
  37 #define OPT_ARGS        "P:S:C:n:r:w:d:psulo"
  38
  39 static struct {
  40         char *path;
  41         char *name;
  42         char **jail_argv;
  43         char *seccomp;
  44         char *capabilities;
  45         int procfs;
  46         int ronly;
  47         int sysfs;
  48 } opts;
  49
  50 struct extra {
  51         struct list_head list;
  52
  53         const char *path;
  54         const char *name;
  55         int readonly;
  56 };
  57
  58 static LIST_HEAD(extras);
  59
  60 extern int pivot_root(const char *new_root, const char *put_old);
  61
  62 int debug = 0;
  63
  64 static char child_stack[STACK_SIZE];
  65
  66 static int mkdir_p(char *dir, mode_t mask)
  67 {
  68         char *l = strrchr(dir, '/');
  69         int ret;
  70
  71         if (!l)
  72                 return 0;
  73
  74         *l = '\0';
  75
  76         if (mkdir_p(dir, mask))
  77                 return -1;
  78
  79         *l = '/';
  80
  81         ret = mkdir(dir, mask);
  82         if (ret && errno == EEXIST)
  83                 return 0;
  84
  85         if (ret)
  86                 ERROR("mkdir failed on %s: %s\n", dir, strerror(errno));
  87
  88         return ret;
  89 }
  90
  91 static int mount_bind(const char *root, const char *path, const char *name, int readonly, int error)
  92 {
  93         const char *p = path;
  94         struct stat s;
  95         char old[256];
  96         char new[256];
  97         int fd;
  98
  99         if (strstr(p, "local"))
 100                 p = "/lib";
 101
 102         snprintf(old, sizeof(old), "%s/%s", path, name);
 103         snprintf(new, sizeof(new), "%s%s", root, p);
 104
 105         mkdir_p(new, 0755);
 106
 107         snprintf(new, sizeof(new), "%s%s/%s", root, p, name);
 108
 109         if (stat(old, &s)) {
 110                 ERROR("%s does not exist\n", old);
 111                 return error;
 112         }
 113
 114         if (S_ISDIR(s.st_mode)) {
 115                 mkdir_p(new, 0755);
 116         } else {
 117                 fd = creat(new, 0644);
 118                 if (fd == -1) {
 119                         ERROR("failed to create %s: %s\n", new, strerror(errno));
 120                         return -1;
 121                 }
 122                 close(fd);
 123         }
 124
 125         if (mount(old, new, NULL, MS_BIND, NULL)) {
 126                 ERROR("failed to mount -B %s %s: %s\n", old, new, strerror(errno));
 127                 return -1;
 128         }
 129
 130         if (readonly && mount(NULL, new, NULL, MS_BIND | MS_REMOUNT | MS_RDONLY, NULL)) {
 131                 ERROR("failed to remount ro %s: %s\n", new, strerror(errno));
 132                 return -1;
 133         }
 134
 135         DEBUG("mount -B %s %s\n", old, new);
 136
 137         return 0;
 138 }
 139
 140 static int build_jail_fs()
 141 {
 142         struct library *l;
 143         struct extra *m;
 144
 145         if (mount("tmpfs", opts.path, "tmpfs", MS_NOATIME, "mode=0755")) {
 146                 ERROR("tmpfs mount failed %s\n", strerror(errno));
 147                 return -1;
 148         }
 149
 150         if (chdir(opts.path)) {
 151                 ERROR("failed to chdir() in the jail root\n");
 152                 return -1;
 153         }
 154
 155         avl_init(&libraries, avl_strcmp, false, NULL);
 156         alloc_library_path("/lib64");
 157         alloc_library_path("/lib");
 158         alloc_library_path("/usr/lib");
 159         load_ldso_conf("/etc/ld.so.conf");
 160
 161         if (elf_load_deps(*opts.jail_argv)) {
 162                 ERROR("failed to load dependencies\n");
 163                 return -1;
 164         }
 165
 166         if (opts.seccomp && elf_load_deps("libpreload-seccomp.so")) {
 167                 ERROR("failed to load libpreload-seccomp.so\n");
 168                 return -1;
 169         }
 170
 171         avl_for_each_element(&libraries, l, avl)
 172                 if (mount_bind(opts.path, l->path, l->name, 1, -1))
 173                         return -1;
 174
 175         list_for_each_entry(m, &extras, list)
 176                 if (mount_bind(opts.path, m->path, m->name, m->readonly, 0))
 177                         return -1;
 178
 179         char *mpoint;
 180         if (asprintf(&mpoint, "%s/old", opts.path) < 0) {
 181                 ERROR("failed to alloc pivot path: %s\n", strerror(errno));
 182                 return -1;
 183         }
 184         mkdir_p(mpoint, 0755);
 185         if (pivot_root(opts.path, mpoint) == -1) {
 186                 ERROR("pivot_root failed:%s\n", strerror(errno));
 187                 free(mpoint);
 188                 return -1;
 189         }
 190         free(mpoint);
 191         umount2("/old", MNT_DETACH);
 192         rmdir("/old");
 193         if (opts.procfs) {
 194                 mkdir("/proc", 0755);
 195                 mount("proc", "/proc", "proc", MS_NOATIME, 0);
 196         }
 197         if (opts.sysfs) {
 198                 mkdir("/sys", 0755);
 199                 mount("sysfs", "/sys", "sysfs", MS_NOATIME, 0);
 200         }
 201         if (opts.ronly)
 202                 mount(NULL, "/", NULL, MS_RDONLY | MS_REMOUNT, 0);
 203
 204         return 0;
 205 }
 206
 207 #define MAX_ENVP        8
 208 static char** build_envp(const char *seccomp)
 209 {
 210         static char *envp[MAX_ENVP];
 211         static char preload_var[64];
 212         static char seccomp_var[64];
 213         static char debug_var[] = "LD_DEBUG=all";
 214         char *preload_lib = find_lib("libpreload-seccomp.so");
 215         int count = 0;
 216
 217         if (seccomp && !preload_lib) {
 218                 ERROR("failed to add preload-lib to env\n");
 219                 return NULL;
 220         }
 221         if (seccomp) {
 222                 snprintf(seccomp_var, sizeof(seccomp_var), "SECCOMP_FILE=%s", seccomp);
 223                 envp[count++] = seccomp_var;
 224                 snprintf(preload_var, sizeof(preload_var), "LD_PRELOAD=%s", preload_lib);
 225                 envp[count++] = preload_var;
 226         }
 227         if (debug > 1)
 228                 envp[count++] = debug_var;
 229
 230         return envp;
 231 }
 232
 233 static void usage(void)
 234 {
 235         fprintf(stderr, "ujail <options> -- <binary> <params ...>\n");
 236         fprintf(stderr, "  -P <path>\tpath where the jail will be staged\n");
 237         fprintf(stderr, "  -S <file>\tseccomp filter\n");
 238         fprintf(stderr, "  -C <file>\tcapabilities drop config\n");
 239         fprintf(stderr, "  -n <name>\tthe name of the jail\n");
 240         fprintf(stderr, "  -r <file>\treadonly files that should be staged\n");
 241         fprintf(stderr, "  -w <file>\twriteable files that should be staged\n");
 242         fprintf(stderr, "  -d <num>\tshow debug log (increase num to increase verbosity)\n");
 243         fprintf(stderr, "  -p\t\tjail has /proc\n");
 244         fprintf(stderr, "  -s\t\tjail has /sys\n");
 245         fprintf(stderr, "  -l\t\tjail has /dev/log\n");
 246         fprintf(stderr, "  -u\t\tjail has a ubus socket\n");
 247         fprintf(stderr, "  -o\t\tremont jail root (/) read only\n");
 248         fprintf(stderr, "\nWarning: by default root inside the jail is the same\n\
 249 and he has the same powers as root outside the jail,\n\
 250 thus he can escape the jail and/or break stuff.\n\
 251 Please use an appropriate seccomp/capabilities filter (-S/-C) to restrict his powers\n");
 252 }
 253
 254 static int spawn_jail(void *arg)
 255 {
 256         if (opts.name && sethostname(opts.name, strlen(opts.name))) {
 257                 ERROR("failed to sethostname: %s\n", strerror(errno));
 258         }
 259
 260         if (build_jail_fs()) {
 261                 ERROR("failed to build jail fs");
 262                 exit(EXIT_FAILURE);
 263         }
 264
 265         char **envp = build_envp(opts.seccomp);
 266         if (!envp)
 267                 exit(EXIT_FAILURE);
 268
 269         if (opts.capabilities && drop_capabilities(opts.capabilities))
 270                 exit(EXIT_FAILURE);
 271
 272         INFO("exec-ing %s\n", *opts.jail_argv);
 273         execve(*opts.jail_argv, opts.jail_argv, envp);
 274         //we get there only if execve fails
 275         ERROR("failed to execve %s: %s\n", *opts.jail_argv, strerror(errno));
 276         exit(EXIT_FAILURE);
 277 }
 278
 279 static int jail_running = 1;
 280 static int jail_return_code = 0;
 281
 282 static void jail_process_handler(struct uloop_process *c, int ret)
 283 {
 284         if (WIFEXITED(ret)) {
 285                 jail_return_code = WEXITSTATUS(ret);
 286                 INFO("jail (%d) exited with exit: %d\n", c->pid, jail_return_code);
 287         } else {
 288                 jail_return_code = WTERMSIG(ret);
 289                 INFO("jail (%d) exited with signal: %d\n", c->pid, jail_return_code);
 290         }
 291         jail_running = 0;
 292         uloop_end();
 293 }
 294
 295 static struct uloop_process jail_process = {
 296         .cb = jail_process_handler,
 297 };
 298
 299 static void add_extra(char *name, int readonly)
 300 {
 301         struct extra *f;
 302
 303         if (*name != '/') {
 304                 ERROR("%s is not an absolute path\n", name);
 305                 return;
 306         }
 307
 308         f = calloc(1, sizeof(struct extra));
 309
 310         f->name = basename(name);
 311         f->path = dirname(strdup(name));
 312         f->readonly = readonly;
 313
 314         list_add_tail(&f->list, &extras);
 315 }
 316
 317 int main(int argc, char **argv)
 318 {
 319         uid_t uid = getuid();
 320         char log[] = "/dev/log";
 321         char ubus[] = "/var/run/ubus.sock";
 322         int ret = EXIT_SUCCESS;
 323         int ch;
 324
 325         if (uid) {
 326                 ERROR("not root, aborting: %s\n", strerror(errno));
 327                 return EXIT_FAILURE;
 328         }
 329
 330         umask(022);
 331
 332         while ((ch = getopt(argc, argv, OPT_ARGS)) != -1) {
 333                 switch (ch) {
 334                 case 'd':
 335                         debug = atoi(optarg);
 336                         break;
 337                 case 'p':
 338                         opts.procfs = 1;
 339                         break;
 340                 case 'o':
 341                         opts.ronly = 1;
 342                         break;
 343                 case 's':
 344                         opts.sysfs = 1;
 345                         break;
 346                 case 'S':
 347                         opts.seccomp = optarg;
 348                         add_extra(optarg, 1);
 349                         break;
 350                 case 'C':
 351                         opts.capabilities = optarg;
 352                         add_extra(optarg, 1);
 353                         break;
 354                 case 'P':
 355                         opts.path = optarg;
 356                         break;
 357                 case 'n':
 358                         opts.name = optarg;
 359                         break;
 360                 case 'r':
 361                         add_extra(optarg, 1);
 362                         break;
 363                 case 'w':
 364                         add_extra(optarg, 0);
 365                         break;
 366                 case 'u':
 367                         add_extra(ubus, 0);
 368                         break;
 369                 case 'l':
 370                         add_extra(log, 0);
 371                         break;
 372                 }
 373         }
 374
 375         //no <binary> param found
 376         if (argc - optind < 1) {
 377                 usage();
 378                 return EXIT_FAILURE;
 379         }
 380
 381         opts.jail_argv = &argv[optind];
 382
 383         if (opts.name)
 384                 prctl(PR_SET_NAME, opts.name, NULL, NULL, NULL);
 385
 386         if (!opts.path && asprintf(&opts.path, "/tmp/%s", basename(*opts.jail_argv)) == -1) {
 387                 ERROR("failed to asprintf root path: %s\n", strerror(errno));
 388                 return EXIT_FAILURE;
 389         }
 390
 391         if (mkdir(opts.path, 0755)) {
 392                 ERROR("unable to create root path: %s (%s)\n", opts.path, strerror(errno));
 393                 return EXIT_FAILURE;
 394         }
 395
 396         uloop_init();
 397         jail_process.pid = clone(spawn_jail,
 398                         child_stack + STACK_SIZE,
 399                         CLONE_NEWUTS | CLONE_NEWPID | CLONE_NEWNS | CLONE_NEWIPC | SIGCHLD, argv);
 400
 401         if (jail_process.pid != -1) {
 402                 uloop_process_add(&jail_process);
 403                 uloop_run();
 404                 uloop_done();
 405                 if (jail_running) {
 406                         kill(jail_process.pid, SIGTERM);
 407                         waitpid(jail_process.pid, NULL, 0);
 408                 }
 409         } else {
 410                 ERROR("failed to spawn namespace: %s\n", strerror(errno));
 411                 ret = EXIT_FAILURE;
 412         }
 413
 414         if (rmdir(opts.path)) {
 415                 ERROR("Unable to remove root path: %s (%s)\n", opts.path, strerror(errno));
 416                 ret = EXIT_FAILURE;
 417         }
 418
 419         if (ret)
 420                 return ret;
 421
 422         return jail_return_code;
 423 }