src/lxc/tools/lxc_attach.c

   1 /*
   2  * lxc: linux Container library
   3  *
   4  * (C) Copyright IBM Corp. 2007, 2010
   5  *
   6  * Authors:
   7  * Daniel Lezcano <daniel.lezcano at free.fr>
   8  *
   9  * This library is free software; you can redistribute it and/or
  10  * modify it under the terms of the GNU Lesser General Public
  11  * License as published by the Free Software Foundation; either
  12  * version 2.1 of the License, or (at your option) any later version.
  13  *
  14  * This library is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  17  * Lesser General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU Lesser General Public
  20  * License along with this library; if not, write to the Free Software
  21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  22  */
  23
  24 #ifndef _GNU_SOURCE
  25 #define _GNU_SOURCE 1
  26 #endif
  27 #include <errno.h>
  28 #include <fcntl.h>
  29 #include <stdio.h>
  30 #include <stdlib.h>
  31 #include <string.h>
  32 #include <sys/ioctl.h>
  33 #include <sys/stat.h>
  34 #include <sys/types.h>
  35 #include <sys/wait.h>
  36 #include <termios.h>
  37 #include <unistd.h>
  38
  39 #include <lxc/lxccontainer.h>
  40
  41 #include "arguments.h"
  42 #include "attach.h"
  43 #include "caps.h"
  44 #include "config.h"
  45 #include "confile.h"
  46 #include "log.h"
  47 #include "rexec.h"
  48 #include "utils.h"
  49
  50 lxc_log_define(lxc_attach, lxc);
  51
  52 /**
  53  * This function will copy any binary that calls liblxc into a memory file and
  54  * will use the memfd to rexecute the binary. This is done to prevent attacks
  55  * through the /proc/self/exe symlink to corrupt the host binary when host and
  56  * container are in the same user namespace or have set up an identity id
  57  * mapping: CVE-2019-5736.
  58  */
  59 #ifdef ENFORCE_MEMFD_REXEC
  60 __attribute__((constructor)) static void lxc_attach_rexec(void)
  61 {
  62         if (!getenv("LXC_MEMFD_REXEC") && lxc_rexec("lxc-attach")) {
  63                 fprintf(stderr, "Failed to re-execute lxc-attach via memory file descriptor\n");
  64                 _exit(EXIT_FAILURE);
  65         }
  66 }
  67 #endif
  68
  69 static int my_parser(struct lxc_arguments *args, int c, char *arg);
  70 static int add_to_simple_array(char ***array, ssize_t *capacity, char *value);
  71 static bool stdfd_is_pty(void);
  72 static int lxc_attach_create_log_file(const char *log_file);
  73
  74 static int elevated_privileges;
  75 static signed long new_personality = -1;
  76 static int namespace_flags = -1;
  77 static int remount_sys_proc;
  78 static lxc_attach_env_policy_t env_policy = LXC_ATTACH_KEEP_ENV;
  79 static char **extra_env;
  80 static ssize_t extra_env_size;
  81 static char **extra_keep;
  82 static ssize_t extra_keep_size;
  83
  84 static const struct option my_longopts[] = {
  85         {"elevated-privileges", optional_argument, 0, 'e'},
  86         {"arch", required_argument, 0, 'a'},
  87         {"namespaces", required_argument, 0, 's'},
  88         {"remount-sys-proc", no_argument, 0, 'R'},
  89         /* TODO: decide upon short option names */
  90         {"clear-env", no_argument, 0, 500},
  91         {"keep-env", no_argument, 0, 501},
  92         {"keep-var", required_argument, 0, 502},
  93         {"set-var", required_argument, 0, 'v'},
  94         {"pty-log", required_argument, 0, 'L'},
  95         {"rcfile", required_argument, 0, 'f'},
  96         {"uid", required_argument, 0, 'u'},
  97         {"gid", required_argument, 0, 'g'},
  98         LXC_COMMON_OPTIONS
  99 };
 100
 101 static struct lxc_arguments my_args = {
 102         .progname     = "lxc-attach",
 103         .help         = "\
 104 --name=NAME [-- COMMAND]\n\
 105 \n\
 106 Execute the specified COMMAND - enter the container NAME\n\
 107 \n\
 108 Options :\n\
 109   -n, --name=NAME   NAME of the container\n\
 110   -e, --elevated-privileges=PRIVILEGES\n\
 111                     Use elevated privileges instead of those of the\n\
 112                     container. If you don't specify privileges to be\n\
 113                     elevated as OR'd list: CAP, CGROUP and LSM (capabilities,\n\
 114                     cgroup and restrictions, respectively) then all of them\n\
 115                     will be elevated.\n\
 116                     WARNING: This may leak privileges into the container.\n\
 117                     Use with care.\n\
 118   -a, --arch=ARCH   Use ARCH for program instead of container's own\n\
 119                     architecture.\n\
 120   -s, --namespaces=FLAGS\n\
 121                     Don't attach to all the namespaces of the container\n\
 122                     but just to the following OR'd list of flags:\n\
 123                     MOUNT, PID, UTSNAME, IPC, USER or NETWORK.\n\
 124                     WARNING: Using -s implies -e with all privileges\n\
 125                     elevated, it may therefore leak privileges into the\n\
 126                     container. Use with care.\n\
 127   -R, --remount-sys-proc\n\
 128                     Remount /sys and /proc if not attaching to the\n\
 129                     mount namespace when using -s in order to properly\n\
 130                     reflect the correct namespace context. See the\n\
 131                     lxc-attach(1) manual page for details.\n\
 132       --clear-env   Clear all environment variables before attaching.\n\
 133                     The attached shell/program will start with only\n\
 134                     container=lxc set.\n\
 135       --keep-env    Keep all current environment variables. This\n\
 136                     is the current default behaviour, but is likely to\n\
 137                     change in the future.\n\
 138   -L, --pty-log=FILE\n\
 139                     Log pty output to FILE\n\
 140   -v, --set-var     Set an additional variable that is seen by the\n\
 141                     attached program in the container. May be specified\n\
 142                     multiple times.\n\
 143       --keep-var    Keep an additional environment variable. Only\n\
 144                     applicable if --clear-env is specified. May be used\n\
 145                     multiple times.\n\
 146   -f, --rcfile=FILE\n\
 147                     Load configuration file FILE\n\
 148   -u, --uid=UID     Execute COMMAND with UID inside the container\n\
 149   -g, --gid=GID     Execute COMMAND with GID inside the container\n\
 150 ",
 151         .options      = my_longopts,
 152         .parser       = my_parser,
 153         .checker      = NULL,
 154         .log_priority = "ERROR",
 155         .log_file     = "none",
 156 };
 157
 158 static int my_parser(struct lxc_arguments *args, int c, char *arg)
 159 {
 160         int ret;
 161
 162         switch (c) {
 163         case 'e':
 164                 ret = lxc_fill_elevated_privileges(arg, &elevated_privileges);
 165                 if (ret)
 166                         return -1;
 167                 break;
 168         case 'R': remount_sys_proc = 1; break;
 169         case 'a':
 170                 new_personality = lxc_config_parse_arch(arg);
 171                 if (new_personality < 0) {
 172                         ERROR("Invalid architecture specified: %s", arg);
 173                         return -1;
 174                 }
 175                 break;
 176         case 's':
 177                 namespace_flags = 0;
 178
 179                 if (lxc_namespace_2_std_identifiers(arg) < 0)
 180                         return -1;
 181
 182                 ret = lxc_fill_namespace_flags(arg, &namespace_flags);
 183                 if (ret)
 184                         return -1;
 185
 186                 /* -s implies -e */
 187                 lxc_fill_elevated_privileges(NULL, &elevated_privileges);
 188                 break;
 189         case 500: /* clear-env */
 190                 env_policy = LXC_ATTACH_CLEAR_ENV;
 191                 break;
 192         case 501: /* keep-env */
 193                 env_policy = LXC_ATTACH_KEEP_ENV;
 194                 break;
 195         case 502: /* keep-var */
 196                 ret = add_to_simple_array(&extra_keep, &extra_keep_size, arg);
 197                 if (ret < 0) {
 198                         ERROR("Failed to alloc memory");
 199                         return -1;
 200                 }
 201                 break;
 202         case 'v':
 203                 ret = add_to_simple_array(&extra_env, &extra_env_size, arg);
 204                 if (ret < 0) {
 205                         ERROR("Failed to alloc memory");
 206                         return -1;
 207                 }
 208                 break;
 209         case 'L':
 210                 args->console_log = arg;
 211                 break;
 212         case 'f':
 213                 args->rcfile = arg;
 214                 break;
 215         case 'u':
 216                 if (lxc_safe_uint(arg, &args->uid) < 0)
 217                         return -1;
 218                 break;
 219         case 'g':
 220                 if (lxc_safe_uint(arg, &args->gid) < 0)
 221                         return -1;
 222                 break;
 223         }
 224
 225         return 0;
 226 }
 227
 228 static int add_to_simple_array(char ***array, ssize_t *capacity, char *value)
 229 {
 230         ssize_t count = 0;
 231
 232         if (!array)
 233                 return -1;
 234
 235         if (*array)
 236                 for (; (*array)[count]; count++);
 237
 238         /* we have to reallocate */
 239         if (count >= *capacity - 1) {
 240                 ssize_t new_capacity = ((count + 1) / 32 + 1) * 32;
 241
 242                 char **new_array = realloc((void*)*array, sizeof(char *) * new_capacity);
 243                 if (!new_array)
 244                         return -1;
 245
 246                 memset(&new_array[count], 0, sizeof(char*)*(new_capacity - count));
 247
 248                 *array = new_array;
 249                 *capacity = new_capacity;
 250         }
 251
 252         if (!(*array))
 253                 return -1;
 254
 255         (*array)[count] = value;
 256         return 0;
 257 }
 258
 259 static bool stdfd_is_pty(void)
 260 {
 261         if (isatty(STDIN_FILENO))
 262                 return true;
 263
 264         if (isatty(STDOUT_FILENO))
 265                 return true;
 266
 267         if (isatty(STDERR_FILENO))
 268                 return true;
 269
 270         return false;
 271 }
 272
 273 static int lxc_attach_create_log_file(const char *log_file)
 274 {
 275         int fd;
 276
 277         fd = open(log_file, O_CLOEXEC | O_RDWR | O_CREAT | O_APPEND, 0600);
 278         if (fd < 0) {
 279                 ERROR("Failed to open log file \"%s\"", log_file);
 280                 return -1;
 281         }
 282
 283         return fd;
 284 }
 285
 286 int main(int argc, char *argv[])
 287 {
 288         int ret = -1;
 289         int wexit = 0;
 290         struct lxc_log log;
 291         pid_t pid;
 292         lxc_attach_options_t attach_options = LXC_ATTACH_OPTIONS_DEFAULT;
 293         lxc_attach_command_t command = (lxc_attach_command_t){.program = NULL};
 294
 295         if (lxc_caps_init())
 296                 exit(EXIT_FAILURE);
 297
 298         if (lxc_arguments_parse(&my_args, argc, argv))
 299                 exit(EXIT_FAILURE);
 300
 301         log.name = my_args.name;
 302         log.file = my_args.log_file;
 303         log.level = my_args.log_priority;
 304         log.prefix = my_args.progname;
 305         log.quiet = my_args.quiet;
 306         log.lxcpath = my_args.lxcpath[0];
 307
 308         if (lxc_log_init(&log))
 309                 exit(EXIT_FAILURE);
 310
 311         if (geteuid())
 312                 if (access(my_args.lxcpath[0], O_RDONLY) < 0) {
 313                         ERROR("You lack access to %s", my_args.lxcpath[0]);
 314                         exit(EXIT_FAILURE);
 315                 }
 316
 317         struct lxc_container *c = lxc_container_new(my_args.name, my_args.lxcpath[0]);
 318         if (!c)
 319                 exit(EXIT_FAILURE);
 320
 321         if (my_args.rcfile) {
 322                 c->clear_config(c);
 323                 if (!c->load_config(c, my_args.rcfile)) {
 324                         ERROR("Failed to load rcfile");
 325                         lxc_container_put(c);
 326                         exit(EXIT_FAILURE);
 327                 }
 328
 329                 c->configfile = strdup(my_args.rcfile);
 330                 if (!c->configfile) {
 331                         ERROR("Out of memory setting new config filename");
 332                         lxc_container_put(c);
 333                         exit(EXIT_FAILURE);
 334                 }
 335         }
 336
 337         if (!c->may_control(c)) {
 338                 ERROR("Insufficent privileges to control %s", c->name);
 339                 lxc_container_put(c);
 340                 exit(EXIT_FAILURE);
 341         }
 342
 343         if (remount_sys_proc)
 344                 attach_options.attach_flags |= LXC_ATTACH_REMOUNT_PROC_SYS;
 345
 346         if (elevated_privileges)
 347                 attach_options.attach_flags &= ~(elevated_privileges);
 348
 349         if (stdfd_is_pty())
 350                 attach_options.attach_flags |= LXC_ATTACH_TERMINAL;
 351
 352         attach_options.namespaces = namespace_flags;
 353         attach_options.personality = new_personality;
 354         attach_options.env_policy = env_policy;
 355         attach_options.extra_env_vars = extra_env;
 356         attach_options.extra_keep_env = extra_keep;
 357
 358         if (my_args.argc > 0) {
 359                 command.program = my_args.argv[0];
 360                 command.argv = (char**)my_args.argv;
 361         }
 362
 363         if (my_args.console_log) {
 364                 attach_options.log_fd = lxc_attach_create_log_file(my_args.console_log);
 365                 if (attach_options.log_fd < 0)
 366                         goto out;
 367         }
 368
 369         if (my_args.uid)
 370                 attach_options.uid = my_args.uid;
 371
 372         if (my_args.gid)
 373                 attach_options.gid = my_args.gid;
 374
 375         if (command.program) {
 376                 ret = c->attach_run_wait(c, &attach_options, command.program,
 377                                          (const char **)command.argv);
 378                 if (ret < 0)
 379                         goto out;
 380         } else {
 381                 ret = c->attach(c, lxc_attach_run_shell, NULL, &attach_options, &pid);
 382                 if (ret < 0)
 383                         goto out;
 384
 385                 ret = lxc_wait_for_pid_status(pid);
 386                 if (ret < 0)
 387                         goto out;
 388         }
 389         if (WIFEXITED(ret))
 390                 wexit = WEXITSTATUS(ret);
 391
 392 out:
 393         lxc_container_put(c);
 394         if (ret >= 0)
 395                 exit(wexit);
 396
 397         exit(EXIT_FAILURE);
 398 }