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 namespace;
  46         int procfs;
  47         int ronly;
  48         int sysfs;
  49 } opts;
  50
  51 struct extra {
  52         struct list_head list;
  53
  54         const char *path;
  55         const char *name;
  56         int readonly;
  57 };
  58
  59 static LIST_HEAD(extras);
  60
  61 extern int pivot_root(const char *new_root, const char *put_old);
  62
  63 int debug = 0;
  64
  65 static char child_stack[STACK_SIZE];
  66
  67 static int mkdir_p(char *dir, mode_t mask)
  68 {
  69         char *l = strrchr(dir, '/');
  70         int ret;
  71
  72         if (!l)
  73                 return 0;
  74
  75         *l = '\0';
  76
  77         if (mkdir_p(dir, mask))
  78                 return -1;
  79
  80         *l = '/';
  81
  82         ret = mkdir(dir, mask);
  83         if (ret && errno == EEXIST)
  84                 return 0;
  85
  86         if (ret)
  87                 ERROR("mkdir failed on %s: %s\n", dir, strerror(errno));
  88
  89         return ret;
  90 }
  91
  92 static int mount_bind(const char *root, const char *path, const char *name, int readonly, int error)
  93 {
  94         const char *p = path;
  95         struct stat s;
  96         char old[256];
  97         char new[256];
  98         int fd;
  99
 100         if (strstr(p, "local"))
 101                 p = "/lib";
 102
 103         snprintf(old, sizeof(old), "%s/%s", path, name);
 104         snprintf(new, sizeof(new), "%s%s", root, p);
 105
 106         mkdir_p(new, 0755);
 107
 108         snprintf(new, sizeof(new), "%s%s/%s", root, p, name);
 109
 110         if (stat(old, &s)) {
 111                 ERROR("%s does not exist\n", old);
 112                 return error;
 113         }
 114
 115         if (S_ISDIR(s.st_mode)) {
 116                 mkdir_p(new, 0755);
 117         } else {
 118                 fd = creat(new, 0644);
 119                 if (fd == -1) {
 120                         ERROR("failed to create %s: %s\n", new, strerror(errno));
 121                         return -1;
 122                 }
 123                 close(fd);
 124         }
 125
 126         if (mount(old, new, NULL, MS_BIND, NULL)) {
 127                 ERROR("failed to mount -B %s %s: %s\n", old, new, strerror(errno));
 128                 return -1;
 129         }
 130
 131         if (readonly && mount(NULL, new, NULL, MS_BIND | MS_REMOUNT | MS_RDONLY, NULL)) {
 132                 ERROR("failed to remount ro %s: %s\n", new, strerror(errno));
 133                 return -1;
 134         }
 135
 136         DEBUG("mount -B %s %s\n", old, new);
 137
 138         return 0;
 139 }
 140
 141 static int build_jail_fs()
 142 {
 143         struct library *l;
 144         struct extra *m;
 145
 146         if (mount("tmpfs", opts.path, "tmpfs", MS_NOATIME, "mode=0755")) {
 147                 ERROR("tmpfs mount failed %s\n", strerror(errno));
 148                 return -1;
 149         }
 150
 151         if (chdir(opts.path)) {
 152                 ERROR("failed to chdir() in the jail root\n");
 153                 return -1;
 154         }
 155
 156         avl_init(&libraries, avl_strcmp, false, NULL);
 157         alloc_library_path("/lib64");
 158         alloc_library_path("/lib");
 159         alloc_library_path("/usr/lib");
 160         load_ldso_conf("/etc/ld.so.conf");
 161
 162         if (elf_load_deps(*opts.jail_argv)) {
 163                 ERROR("failed to load dependencies\n");
 164                 return -1;
 165         }
 166
 167         if (opts.seccomp && elf_load_deps("libpreload-seccomp.so")) {
 168                 ERROR("failed to load libpreload-seccomp.so\n");
 169                 return -1;
 170         }
 171
 172         avl_for_each_element(&libraries, l, avl)
 173                 if (mount_bind(opts.path, l->path, l->name, 1, -1))
 174                         return -1;
 175
 176         list_for_each_entry(m, &extras, list)
 177                 if (mount_bind(opts.path, m->path, m->name, m->readonly, 0))
 178                         return -1;
 179
 180         char *mpoint;
 181         if (asprintf(&mpoint, "%s/old", opts.path) < 0) {
 182                 ERROR("failed to alloc pivot path: %s\n", strerror(errno));
 183                 return -1;
 184         }
 185         mkdir_p(mpoint, 0755);
 186         if (pivot_root(opts.path, mpoint) == -1) {
 187                 ERROR("pivot_root failed:%s\n", strerror(errno));
 188                 free(mpoint);
 189                 return -1;
 190         }
 191         free(mpoint);
 192         umount2("/old", MNT_DETACH);
 193         rmdir("/old");
 194         if (opts.procfs) {
 195                 mkdir("/proc", 0755);
 196                 mount("proc", "/proc", "proc", MS_NOATIME, 0);
 197         }
 198         if (opts.sysfs) {
 199                 mkdir("/sys", 0755);
 200                 mount("sysfs", "/sys", "sysfs", MS_NOATIME, 0);
 201         }
 202         if (opts.ronly)
 203                 mount(NULL, "/", NULL, MS_RDONLY | MS_REMOUNT, 0);
 204
 205         return 0;
 206 }
 207
 208 #define MAX_ENVP        8
 209 static char** build_envp(const char *seccomp)
 210 {
 211         static char *envp[MAX_ENVP];
 212         static char preload_var[64];
 213         static char seccomp_var[64];
 214         static char debug_var[] = "LD_DEBUG=all";
 215         char *preload_lib = find_lib("libpreload-seccomp.so");
 216         int count = 0;
 217
 218         if (seccomp && !preload_lib) {
 219                 ERROR("failed to add preload-lib to env\n");
 220                 return NULL;
 221         }
 222         if (seccomp) {
 223                 snprintf(seccomp_var, sizeof(seccomp_var), "SECCOMP_FILE=%s", seccomp);
 224                 envp[count++] = seccomp_var;
 225                 snprintf(preload_var, sizeof(preload_var), "LD_PRELOAD=%s", preload_lib);
 226                 envp[count++] = preload_var;
 227         }
 228         if (debug > 1)
 229                 envp[count++] = debug_var;
 230
 231         return envp;
 232 }
 233
 234 static void usage(void)
 235 {
 236         fprintf(stderr, "ujail <options> -- <binary> <params ...>\n");
 237         fprintf(stderr, "  -d <num>\tshow debug log (increase num to increase verbosity)\n");
 238         fprintf(stderr, "  -S <file>\tseccomp filter config\n");
 239         fprintf(stderr, "  -C <file>\tcapabilities drop config\n");
 240         fprintf(stderr, "  -n <name>\tthe name of the jail\n");
 241         fprintf(stderr, "namespace jail options:\n");
 242         fprintf(stderr, "  -P <path>\tpath where the jail will be staged\n");
 243         fprintf(stderr, "  -r <file>\treadonly files that should be staged\n");
 244         fprintf(stderr, "  -w <file>\twriteable files that should be staged\n");
 245         fprintf(stderr, "  -p\t\tjail has /proc\n");
 246         fprintf(stderr, "  -s\t\tjail has /sys\n");
 247         fprintf(stderr, "  -l\t\tjail has /dev/log\n");
 248         fprintf(stderr, "  -u\t\tjail has a ubus socket\n");
 249         fprintf(stderr, "  -o\t\tremont jail root (/) read only\n");
 250         fprintf(stderr, "\nWarning: by default root inside the jail is the same\n\
 251 and he has the same powers as root outside the jail,\n\
 252 thus he can escape the jail and/or break stuff.\n\
 253 Please use seccomp/capabilities (-S/-C) to restrict his powers\n\n\
 254 If you use none of the namespace jail options,\n\
 255 ujail will not use namespace/build a jail,\n\
 256 and will only drop capabilities/apply seccomp filter.\n\n");
 257 }
 258
 259 static int exec_jail()
 260 {
 261         char **envp = build_envp(opts.seccomp);
 262         if (!envp)
 263                 exit(EXIT_FAILURE);
 264
 265         if (opts.capabilities && drop_capabilities(opts.capabilities))
 266                 exit(EXIT_FAILURE);
 267
 268         INFO("exec-ing %s\n", *opts.jail_argv);
 269         execve(*opts.jail_argv, opts.jail_argv, envp);
 270         //we get there only if execve fails
 271         ERROR("failed to execve %s: %s\n", *opts.jail_argv, strerror(errno));
 272         exit(EXIT_FAILURE);
 273 }
 274
 275 static int spawn_jail(void *arg)
 276 {
 277         if (opts.name && sethostname(opts.name, strlen(opts.name))) {
 278                 ERROR("failed to sethostname: %s\n", strerror(errno));
 279         }
 280
 281         if (build_jail_fs()) {
 282                 ERROR("failed to build jail fs");
 283                 exit(EXIT_FAILURE);
 284         }
 285
 286         return exec_jail();
 287 }
 288
 289 static int jail_running = 1;
 290 static int jail_return_code = 0;
 291
 292 static void jail_process_handler(struct uloop_process *c, int ret)
 293 {
 294         if (WIFEXITED(ret)) {
 295                 jail_return_code = WEXITSTATUS(ret);
 296                 INFO("jail (%d) exited with exit: %d\n", c->pid, jail_return_code);
 297         } else {
 298                 jail_return_code = WTERMSIG(ret);
 299                 INFO("jail (%d) exited with signal: %d\n", c->pid, jail_return_code);
 300         }
 301         jail_running = 0;
 302         uloop_end();
 303 }
 304
 305 static struct uloop_process jail_process = {
 306         .cb = jail_process_handler,
 307 };
 308
 309 static void add_extra(char *name, int readonly)
 310 {
 311         struct extra *f;
 312
 313         if (*name != '/') {
 314                 ERROR("%s is not an absolute path\n", name);
 315                 return;
 316         }
 317
 318         f = calloc(1, sizeof(struct extra));
 319
 320         f->name = basename(name);
 321         f->path = dirname(strdup(name));
 322         f->readonly = readonly;
 323
 324         list_add_tail(&f->list, &extras);
 325 }
 326
 327 int main(int argc, char **argv)
 328 {
 329         uid_t uid = getuid();
 330         char log[] = "/dev/log";
 331         char ubus[] = "/var/run/ubus.sock";
 332         int ret = EXIT_SUCCESS;
 333         int ch;
 334
 335         if (uid) {
 336                 ERROR("not root, aborting: %s\n", strerror(errno));
 337                 return EXIT_FAILURE;
 338         }
 339
 340         umask(022);
 341
 342         while ((ch = getopt(argc, argv, OPT_ARGS)) != -1) {
 343                 switch (ch) {
 344                 case 'd':
 345                         debug = atoi(optarg);
 346                         break;
 347                 case 'p':
 348                         opts.namespace = 1;
 349                         opts.procfs = 1;
 350                         break;
 351                 case 'o':
 352                         opts.namespace = 1;
 353                         opts.ronly = 1;
 354                         break;
 355                 case 's':
 356                         opts.namespace = 1;
 357                         opts.sysfs = 1;
 358                         break;
 359                 case 'S':
 360                         opts.seccomp = optarg;
 361                         add_extra(optarg, 1);
 362                         break;
 363                 case 'C':
 364                         opts.capabilities = optarg;
 365                         add_extra(optarg, 1);
 366                         break;
 367                 case 'P':
 368                         opts.namespace = 1;
 369                         opts.path = optarg;
 370                         break;
 371                 case 'n':
 372                         opts.name = optarg;
 373                         break;
 374                 case 'r':
 375                         opts.namespace = 1;
 376                         add_extra(optarg, 1);
 377                         break;
 378                 case 'w':
 379                         opts.namespace = 1;
 380                         add_extra(optarg, 0);
 381                         break;
 382                 case 'u':
 383                         opts.namespace = 1;
 384                         add_extra(ubus, 0);
 385                         break;
 386                 case 'l':
 387                         opts.namespace = 1;
 388                         add_extra(log, 0);
 389                         break;
 390                 }
 391         }
 392
 393         //no <binary> param found
 394         if (argc - optind < 1) {
 395                 usage();
 396                 return EXIT_FAILURE;
 397         }
 398         if (!(opts.namespace||opts.capabilities||opts.seccomp)) {
 399                 ERROR("Not using namespaces, capabilities or seccomp !!!\n\n");
 400                 usage();
 401                 return EXIT_FAILURE;
 402         }
 403         DEBUG("Using namespaces(%d), capabilities(%d), seccomp(%d)\n",
 404                 opts.namespace,
 405                 opts.capabilities != 0,
 406                 opts.seccomp != 0);
 407
 408         opts.jail_argv = &argv[optind];
 409
 410         if (opts.name)
 411                 prctl(PR_SET_NAME, opts.name, NULL, NULL, NULL);
 412
 413         if (opts.namespace && !opts.path && asprintf(&opts.path, "/tmp/%s", basename(*opts.jail_argv)) == -1) {
 414                 ERROR("failed to asprintf root path: %s\n", strerror(errno));
 415                 return EXIT_FAILURE;
 416         }
 417
 418         if (opts.namespace && mkdir(opts.path, 0755)) {
 419                 ERROR("unable to create root path: %s (%s)\n", opts.path, strerror(errno));
 420                 return EXIT_FAILURE;
 421         }
 422
 423         uloop_init();
 424         if (opts.namespace) {
 425                 jail_process.pid = clone(spawn_jail,
 426                         child_stack + STACK_SIZE,
 427                         CLONE_NEWUTS | CLONE_NEWPID | CLONE_NEWNS | CLONE_NEWIPC | SIGCHLD, argv);
 428         } else {
 429                 jail_process.pid = fork();
 430         }
 431
 432         if (jail_process.pid > 0) {
 433                 //parent process
 434                 uloop_process_add(&jail_process);
 435                 uloop_run();
 436                 uloop_done();
 437                 if (jail_running) {
 438                         DEBUG("uloop interrupted, killing jail process\n");
 439                         kill(jail_process.pid, SIGTERM);
 440                         waitpid(jail_process.pid, NULL, 0);
 441                 }
 442         } else if (jail_process.pid == 0) {
 443                 //fork child process
 444                 return exec_jail();
 445         } else {
 446                 ERROR("failed to clone/fork: %s\n", strerror(errno));
 447                 ret = EXIT_FAILURE;
 448         }
 449
 450         if (opts.namespace && rmdir(opts.path)) {
 451                 ERROR("Unable to remove root path: %s (%s)\n", opts.path, strerror(errno));
 452                 ret = EXIT_FAILURE;
 453         }
 454
 455         if (ret)
 456                 return ret;
 457
 458         return jail_return_code;
 459 }