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:d:psulo"
  47
  48 static struct {
  49         char *path;
  50         char *name;
  51         char **jail_argv;
  52         char *seccomp;
  53         int procfs;
  54         int ronly;
  55         int sysfs;
  56 } opts;
  57
  58 struct extra {
  59         struct list_head list;
  60
  61         const char *path;
  62         const char *name;
  63         int readonly;
  64 };
  65
  66 static LIST_HEAD(extras);
  67
  68 extern int pivot_root(const char *new_root, const char *put_old);
  69
  70 int debug = 0;
  71
  72 static char child_stack[STACK_SIZE];
  73
  74 static int mkdir_p(char *dir, mode_t mask)
  75 {
  76         char *l = strrchr(dir, '/');
  77         int ret;
  78
  79         if (!l)
  80                 return 0;
  81
  82         *l = '\0';
  83
  84         if (mkdir_p(dir, mask))
  85                 return -1;
  86
  87         *l = '/';
  88
  89         ret = mkdir(dir, mask);
  90         if (ret && errno == EEXIST)
  91                 return 0;
  92
  93         if (ret)
  94                 ERROR("mkdir failed on %s: %s\n", dir, strerror(errno));
  95
  96         return ret;
  97 }
  98
  99 static int mount_bind(const char *root, const char *path, const char *name, int readonly, int error)
 100 {
 101         const char *p = path;
 102         struct stat s;
 103         char old[256];
 104         char new[256];
 105         int fd;
 106
 107         if (strstr(p, "local"))
 108                 p = "/lib";
 109
 110         snprintf(old, sizeof(old), "%s/%s", path, name);
 111         snprintf(new, sizeof(new), "%s%s", root, p);
 112
 113         mkdir_p(new, 0755);
 114
 115         snprintf(new, sizeof(new), "%s%s/%s", root, p, name);
 116
 117         if (stat(old, &s)) {
 118                 ERROR("%s does not exist\n", old);
 119                 return error;
 120         }
 121
 122         if (S_ISDIR(s.st_mode)) {
 123                 mkdir_p(new, 0755);
 124         } else {
 125                 fd = creat(new, 0644);
 126                 if (fd == -1) {
 127                         ERROR("failed to create %s: %s\n", new, strerror(errno));
 128                         return -1;
 129                 }
 130                 close(fd);
 131         }
 132
 133         if (mount(old, new, NULL, MS_BIND, NULL)) {
 134                 ERROR("failed to mount -B %s %s: %s\n", old, new, strerror(errno));
 135                 return -1;
 136         }
 137
 138         if (readonly && mount(NULL, new, NULL, MS_BIND | MS_REMOUNT | MS_RDONLY, NULL)) {
 139                 ERROR("failed to remount ro %s: %s\n", new, strerror(errno));
 140                 return -1;
 141         }
 142
 143         DEBUG("mount -B %s %s\n", old, new);
 144
 145         return 0;
 146 }
 147
 148 static int build_jail_fs()
 149 {
 150         struct library *l;
 151         struct extra *m;
 152
 153         if (mount("tmpfs", opts.path, "tmpfs", MS_NOATIME, "mode=0755")) {
 154                 ERROR("tmpfs mount failed %s\n", strerror(errno));
 155                 return -1;
 156         }
 157
 158         if (chdir(opts.path)) {
 159                 ERROR("failed to chdir() in the jail root\n");
 160                 return -1;
 161         }
 162
 163         avl_init(&libraries, avl_strcmp, false, NULL);
 164         alloc_library_path("/lib64");
 165         alloc_library_path("/lib");
 166         alloc_library_path("/usr/lib");
 167         load_ldso_conf("/etc/ld.so.conf");
 168
 169         if (elf_load_deps(*opts.jail_argv)) {
 170                 ERROR("failed to load dependencies\n");
 171                 return -1;
 172         }
 173
 174         if (opts.seccomp && elf_load_deps("libpreload-seccomp.so")) {
 175                 ERROR("failed to load libpreload-seccomp.so\n");
 176                 return -1;
 177         }
 178
 179         avl_for_each_element(&libraries, l, avl)
 180                 if (mount_bind(opts.path, l->path, l->name, 1, -1))
 181                         return -1;
 182
 183         list_for_each_entry(m, &extras, list)
 184                 if (mount_bind(opts.path, m->path, m->name, m->readonly, 0))
 185                         return -1;
 186
 187         char *mpoint;
 188         if (asprintf(&mpoint, "%s/old", opts.path) < 0) {
 189                 ERROR("failed to alloc pivot path: %s\n", strerror(errno));
 190                 return -1;
 191         }
 192         mkdir_p(mpoint, 0755);
 193         if (pivot_root(opts.path, mpoint) == -1) {
 194                 ERROR("pivot_root failed:%s\n", strerror(errno));
 195                 free(mpoint);
 196                 return -1;
 197         }
 198         free(mpoint);
 199         umount2("/old", MNT_DETACH);
 200         rmdir("/old");
 201         if (opts.procfs) {
 202                 mkdir("/proc", 0755);
 203                 mount("proc", "/proc", "proc", MS_NOATIME, 0);
 204         }
 205         if (opts.sysfs) {
 206                 mkdir("/sys", 0755);
 207                 mount("sysfs", "/sys", "sysfs", MS_NOATIME, 0);
 208         }
 209         if (opts.ronly)
 210                 mount(NULL, "/", NULL, MS_RDONLY | MS_REMOUNT, 0);
 211
 212         return 0;
 213 }
 214
 215 #define MAX_ENVP        8
 216 static char** build_envp(const char *seccomp)
 217 {
 218         static char *envp[MAX_ENVP];
 219         static char preload_var[64];
 220         static char seccomp_var[64];
 221         static char debug_var[] = "LD_DEBUG=all";
 222         char *preload_lib = find_lib("libpreload-seccomp.so");
 223         int count = 0;
 224
 225         if (seccomp && !preload_lib) {
 226                 ERROR("failed to add preload-lib to env\n");
 227                 return NULL;
 228         }
 229         if (seccomp) {
 230                 snprintf(seccomp_var, sizeof(seccomp_var), "SECCOMP_FILE=%s", seccomp);
 231                 envp[count++] = seccomp_var;
 232                 snprintf(preload_var, sizeof(preload_var), "LD_PRELOAD=%s", preload_lib);
 233                 envp[count++] = preload_var;
 234         }
 235         if (debug > 1)
 236                 envp[count++] = debug_var;
 237
 238         return envp;
 239 }
 240
 241 static void usage(void)
 242 {
 243         fprintf(stderr, "ujail <options> -- <binary> <params ...>\n");
 244         fprintf(stderr, "  -P <path>\tpath where the jail will be staged\n");
 245         fprintf(stderr, "  -S <file>\tseccomp filter\n");
 246         fprintf(stderr, "  -n <name>\tthe name of the jail\n");
 247         fprintf(stderr, "  -r <file>\treadonly files that should be staged\n");
 248         fprintf(stderr, "  -w <file>\twriteable files that should be staged\n");
 249         fprintf(stderr, "  -d <num>\tshow debug log (increase num to increase verbosity)\n");
 250         fprintf(stderr, "  -p\t\tjail has /proc\n");
 251         fprintf(stderr, "  -s\t\tjail has /sys\n");
 252         fprintf(stderr, "  -l\t\tjail has /dev/log\n");
 253         fprintf(stderr, "  -u\t\tjail has a ubus socket\n");
 254         fprintf(stderr, "  -o\t\tremont jail root (/) read only\n");
 255         fprintf(stderr, "\nWarning: by default root inside the jail is the same\n\
 256 and he has the same powers as root outside the jail,\n\
 257 thus he can escape the jail and/or break stuff.\n\
 258 Please use an appropriate seccomp filter (-S) to restrict his powers\n");
 259 }
 260
 261 static int spawn_jail(void *arg)
 262 {
 263         if (opts.name && sethostname(opts.name, strlen(opts.name))) {
 264                 ERROR("failed to sethostname: %s\n", strerror(errno));
 265         }
 266
 267         if (build_jail_fs()) {
 268                 ERROR("failed to build jail fs");
 269                 exit(EXIT_FAILURE);
 270         }
 271
 272         char **envp = build_envp(opts.seccomp);
 273         if (!envp)
 274                 exit(EXIT_FAILURE);
 275
 276         //TODO: drop capabilities() here
 277         //prctl(PR_CAPBSET_DROP, ..., 0, 0, 0);
 278
 279         INFO("exec-ing %s\n", *opts.jail_argv);
 280         execve(*opts.jail_argv, opts.jail_argv, envp);
 281         //we get there only if execve fails
 282         ERROR("failed to execve %s: %s\n", *opts.jail_argv, strerror(errno));
 283         exit(EXIT_FAILURE);
 284 }
 285
 286 static int jail_running = 1;
 287 static int jail_return_code = 0;
 288
 289 static void jail_process_handler(struct uloop_process *c, int ret)
 290 {
 291         if (WIFEXITED(ret)) {
 292                 jail_return_code = WEXITSTATUS(ret);
 293                 INFO("jail (%d) exited with exit: %d\n", c->pid, jail_return_code);
 294         } else {
 295                 jail_return_code = WTERMSIG(ret);
 296                 INFO("jail (%d) exited with signal: %d\n", c->pid, jail_return_code);
 297         }
 298         jail_running = 0;
 299         uloop_end();
 300 }
 301
 302 static struct uloop_process jail_process = {
 303         .cb = jail_process_handler,
 304 };
 305
 306 static void add_extra(char *name, int readonly)
 307 {
 308         struct extra *f;
 309
 310         if (*name != '/') {
 311                 ERROR("%s is not an absolute path\n", name);
 312                 return;
 313         }
 314
 315         f = calloc(1, sizeof(struct extra));
 316
 317         f->name = basename(name);
 318         f->path = dirname(strdup(name));
 319         f->readonly = readonly;
 320
 321         list_add_tail(&f->list, &extras);
 322 }
 323
 324 int main(int argc, char **argv)
 325 {
 326         uid_t uid = getuid();
 327         char log[] = "/dev/log";
 328         char ubus[] = "/var/run/ubus.sock";
 329         int ret = EXIT_SUCCESS;
 330         int ch;
 331
 332         if (uid) {
 333                 ERROR("not root, aborting: %s\n", strerror(errno));
 334                 return EXIT_FAILURE;
 335         }
 336
 337         umask(022);
 338
 339         while ((ch = getopt(argc, argv, OPT_ARGS)) != -1) {
 340                 switch (ch) {
 341                 case 'd':
 342                         debug = atoi(optarg);
 343                         break;
 344                 case 'p':
 345                         opts.procfs = 1;
 346                         break;
 347                 case 'o':
 348                         opts.ronly = 1;
 349                         break;
 350                 case 's':
 351                         opts.sysfs = 1;
 352                         break;
 353                 case 'S':
 354                         opts.seccomp = optarg;
 355                         add_extra(optarg, 1);
 356                         break;
 357                 case 'P':
 358                         opts.path = optarg;
 359                         break;
 360                 case 'n':
 361                         opts.name = optarg;
 362                         break;
 363                 case 'r':
 364                         add_extra(optarg, 1);
 365                         break;
 366                 case 'w':
 367                         add_extra(optarg, 0);
 368                         break;
 369                 case 'u':
 370                         add_extra(ubus, 0);
 371                         break;
 372                 case 'l':
 373                         add_extra(log, 0);
 374                         break;
 375                 }
 376         }
 377
 378         //no <binary> param found
 379         if (argc - optind < 1) {
 380                 usage();
 381                 return EXIT_FAILURE;
 382         }
 383
 384         opts.jail_argv = &argv[optind];
 385
 386         if (opts.name)
 387                 prctl(PR_SET_NAME, opts.name, NULL, NULL, NULL);
 388
 389         if (!opts.path && asprintf(&opts.path, "/tmp/%s", basename(*opts.jail_argv)) == -1) {
 390                 ERROR("failed to asprintf root path: %s\n", strerror(errno));
 391                 return EXIT_FAILURE;
 392         }
 393
 394         if (mkdir(opts.path, 0755)) {
 395                 ERROR("unable to create root path: %s (%s)\n", opts.path, strerror(errno));
 396                 return EXIT_FAILURE;
 397         }
 398
 399         uloop_init();
 400         jail_process.pid = clone(spawn_jail,
 401                         child_stack + STACK_SIZE,
 402                         CLONE_NEWUTS | CLONE_NEWPID | CLONE_NEWNS | CLONE_NEWIPC | SIGCHLD, argv);
 403
 404         if (jail_process.pid != -1) {
 405                 uloop_process_add(&jail_process);
 406                 uloop_run();
 407                 uloop_done();
 408                 if (jail_running) {
 409                         kill(jail_process.pid, SIGTERM);
 410                         waitpid(jail_process.pid, NULL, 0);
 411                 }
 412         } else {
 413                 ERROR("failed to spawn namespace: %s\n", strerror(errno));
 414                 ret = EXIT_FAILURE;
 415         }
 416
 417         if (rmdir(opts.path)) {
 418                 ERROR("Unable to remove root path: %s (%s)\n", opts.path, strerror(errno));
 419                 ret = EXIT_FAILURE;
 420         }
 421
 422         if (ret)
 423                 return ret;
 424
 425         return jail_return_code;
 426 }