src/lxc/tools/lxc_attach.c

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