src/nspawn/nspawn-bind-user.c

   1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
   2
   3 #include "chase-symlinks.h"
   4 #include "fd-util.h"
   5 #include "fileio.h"
   6 #include "format-util.h"
   7 #include "nspawn-bind-user.h"
   8 #include "nspawn.h"
   9 #include "path-util.h"
  10 #include "user-util.h"
  11 #include "userdb.h"
  12
  13 static int check_etc_passwd_collisions(
  14                 const char *directory,
  15                 const char *name,
  16                 uid_t uid) {
  17
  18         _cleanup_fclose_ FILE *f = NULL;
  19         int r;
  20
  21         assert(directory);
  22         assert(name || uid_is_valid(uid));
  23
  24         r = chase_symlinks_and_fopen_unlocked("/etc/passwd", directory, CHASE_PREFIX_ROOT, "re", NULL, &f);
  25         if (r == -ENOENT)
  26                 return 0; /* no user database? then no user, hence no collision */
  27         if (r < 0)
  28                 return log_error_errno(r, "Failed to open /etc/passwd of container: %m");
  29
  30         for (;;) {
  31                 struct passwd *pw;
  32
  33                 r = fgetpwent_sane(f, &pw);
  34                 if (r < 0)
  35                         return log_error_errno(r, "Failed to iterate through /etc/passwd of container: %m");
  36                 if (r == 0) /* EOF */
  37                         return 0; /* no collision */
  38
  39                 if (name && streq_ptr(pw->pw_name, name))
  40                         return 1; /* name collision */
  41                 if (uid_is_valid(uid) && pw->pw_uid == uid)
  42                         return 1; /* UID collision */
  43         }
  44 }
  45
  46 static int check_etc_group_collisions(
  47                 const char *directory,
  48                 const char *name,
  49                 gid_t gid) {
  50
  51         _cleanup_fclose_ FILE *f = NULL;
  52         int r;
  53
  54         assert(directory);
  55         assert(name || gid_is_valid(gid));
  56
  57         r = chase_symlinks_and_fopen_unlocked("/etc/group", directory, CHASE_PREFIX_ROOT, "re", NULL, &f);
  58         if (r == -ENOENT)
  59                 return 0; /* no group database? then no group, hence no collision */
  60         if (r < 0)
  61                 return log_error_errno(r, "Failed to open /etc/group of container: %m");
  62
  63         for (;;) {
  64                 struct group *gr;
  65
  66                 r = fgetgrent_sane(f, &gr);
  67                 if (r < 0)
  68                         return log_error_errno(r, "Failed to iterate through /etc/group of container: %m");
  69                 if (r == 0)
  70                         return 0; /* no collision */
  71
  72                 if (name && streq_ptr(gr->gr_name, name))
  73                         return 1; /* name collision */
  74                 if (gid_is_valid(gid) && gr->gr_gid == gid)
  75                         return 1; /* gid collision */
  76         }
  77 }
  78
  79 static int convert_user(
  80                 const char *directory,
  81                 UserRecord *u,
  82                 GroupRecord *g,
  83                 uid_t allocate_uid,
  84                 UserRecord **ret_converted_user,
  85                 GroupRecord **ret_converted_group) {
  86
  87         _cleanup_(group_record_unrefp) GroupRecord *converted_group = NULL;
  88         _cleanup_(user_record_unrefp) UserRecord *converted_user = NULL;
  89         _cleanup_free_ char *h = NULL;
  90         JsonVariant *p, *hp = NULL;
  91         int r;
  92
  93         assert(u);
  94         assert(g);
  95         assert(u->gid == g->gid);
  96
  97         r = check_etc_passwd_collisions(directory, u->user_name, UID_INVALID);
  98         if (r < 0)
  99                 return r;
 100         if (r > 0)
 101                 return log_error_errno(SYNTHETIC_ERRNO(EBUSY),
 102                                        "Sorry, the user '%s' already exists in the container.", u->user_name);
 103
 104         r = check_etc_group_collisions(directory, g->group_name, GID_INVALID);
 105         if (r < 0)
 106                 return r;
 107         if (r > 0)
 108                 return log_error_errno(SYNTHETIC_ERRNO(EBUSY),
 109                                        "Sorry, the group '%s' already exists in the container.", g->group_name);
 110
 111         h = path_join("/run/host/home/", u->user_name);
 112         if (!h)
 113                 return log_oom();
 114
 115         /* Acquire the source hashed password array as-is, so that it retains the JSON_VARIANT_SENSITIVE flag */
 116         p = json_variant_by_key(u->json, "privileged");
 117         if (p)
 118                 hp = json_variant_by_key(p, "hashedPassword");
 119
 120         r = user_record_build(
 121                         &converted_user,
 122                         JSON_BUILD_OBJECT(
 123                                         JSON_BUILD_PAIR("userName", JSON_BUILD_STRING(u->user_name)),
 124                                         JSON_BUILD_PAIR("uid", JSON_BUILD_UNSIGNED(allocate_uid)),
 125                                         JSON_BUILD_PAIR("gid", JSON_BUILD_UNSIGNED(allocate_uid)),
 126                                         JSON_BUILD_PAIR_CONDITION(u->disposition >= 0, "disposition", JSON_BUILD_STRING(user_disposition_to_string(u->disposition))),
 127                                         JSON_BUILD_PAIR("homeDirectory", JSON_BUILD_STRING(h)),
 128                                         JSON_BUILD_PAIR("service", JSON_BUILD_CONST_STRING("io.systemd.NSpawn")),
 129                                         JSON_BUILD_PAIR_CONDITION(!strv_isempty(u->hashed_password), "privileged", JSON_BUILD_OBJECT(
 130                                                                                   JSON_BUILD_PAIR("hashedPassword", JSON_BUILD_VARIANT(hp))))));
 131         if (r < 0)
 132                 return log_error_errno(r, "Failed to build container user record: %m");
 133
 134         r = group_record_build(
 135                         &converted_group,
 136                         JSON_BUILD_OBJECT(
 137                                         JSON_BUILD_PAIR("groupName", JSON_BUILD_STRING(g->group_name)),
 138                                         JSON_BUILD_PAIR("gid", JSON_BUILD_UNSIGNED(allocate_uid)),
 139                                         JSON_BUILD_PAIR_CONDITION(g->disposition >= 0, "disposition", JSON_BUILD_STRING(user_disposition_to_string(g->disposition))),
 140                                         JSON_BUILD_PAIR("service", JSON_BUILD_CONST_STRING("io.systemd.NSpawn"))));
 141         if (r < 0)
 142                 return log_error_errno(r, "Failed to build container group record: %m");
 143
 144         *ret_converted_user = TAKE_PTR(converted_user);
 145         *ret_converted_group = TAKE_PTR(converted_group);
 146
 147         return 0;
 148 }
 149
 150 static int find_free_uid(const char *directory, uid_t max_uid, uid_t *current_uid) {
 151         int r;
 152
 153         assert(directory);
 154         assert(current_uid);
 155
 156         for (;; (*current_uid) ++) {
 157                 if (*current_uid > MAP_UID_MAX || *current_uid > max_uid)
 158                         return log_error_errno(
 159                                         SYNTHETIC_ERRNO(EBUSY),
 160                                         "No suitable available UID in range " UID_FMT "…" UID_FMT " in container detected, can't map user.",
 161                                         MAP_UID_MIN, MAP_UID_MAX);
 162
 163                 r = check_etc_passwd_collisions(directory, NULL, *current_uid);
 164                 if (r < 0)
 165                         return r;
 166                 if (r > 0) /* already used */
 167                         continue;
 168
 169                 /* We want to use the UID also as GID, hence check for it in /etc/group too */
 170                 r = check_etc_group_collisions(directory, NULL, (gid_t) *current_uid);
 171                 if (r <= 0)
 172                         return r;
 173         }
 174 }
 175
 176 BindUserContext* bind_user_context_free(BindUserContext *c) {
 177         if (!c)
 178                 return NULL;
 179
 180         assert(c->n_data == 0 || c->data);
 181
 182         for (size_t i = 0; i < c->n_data; i++) {
 183                 user_record_unref(c->data[i].host_user);
 184                 group_record_unref(c->data[i].host_group);
 185                 user_record_unref(c->data[i].payload_user);
 186                 group_record_unref(c->data[i].payload_group);
 187         }
 188
 189         return mfree(c);
 190 }
 191
 192 int bind_user_prepare(
 193                 const char *directory,
 194                 char **bind_user,
 195                 uid_t uid_shift,
 196                 uid_t uid_range,
 197                 CustomMount **custom_mounts,
 198                 size_t *n_custom_mounts,
 199                 BindUserContext **ret) {
 200
 201         _cleanup_(bind_user_context_freep) BindUserContext *c = NULL;
 202         uid_t current_uid = MAP_UID_MIN;
 203         char **n;
 204         int r;
 205
 206         assert(custom_mounts);
 207         assert(n_custom_mounts);
 208         assert(ret);
 209
 210         /* This resolves the users specified in 'bind_user', generates a minimalized JSON user + group record
 211          * for it to stick in the container, allocates a UID/GID for it, and updates the custom mount table,
 212          * to include an appropriate bind mount mapping.
 213          *
 214          * This extends the passed custom_mounts/n_custom_mounts with the home directories, and allocates a
 215          * new BindUserContext for the user records */
 216
 217         if (strv_isempty(bind_user)) {
 218                 *ret = NULL;
 219                 return 0;
 220         }
 221
 222         c = new0(BindUserContext, 1);
 223         if (!c)
 224                 return log_oom();
 225
 226         STRV_FOREACH(n, bind_user) {
 227                 _cleanup_(user_record_unrefp) UserRecord *u = NULL, *cu = NULL;
 228                 _cleanup_(group_record_unrefp) GroupRecord *g = NULL, *cg = NULL;
 229                 _cleanup_free_ char *sm = NULL, *sd = NULL;
 230                 CustomMount *cm;
 231
 232                 r = userdb_by_name(*n, USERDB_DONT_SYNTHESIZE, &u);
 233                 if (r < 0)
 234                         return log_error_errno(r, "Failed to resolve user '%s': %m", *n);
 235
 236                 /* For now, let's refuse mapping the root/nobody users explicitly. The records we generate
 237                  * are strictly additive, nss-systemd is typically placed last in /etc/nsswitch.conf. Thus
 238                  * even if we wanted, we couldn't override the root or nobody user records. Note we also
 239                  * check for name conflicts in /etc/passwd + /etc/group later on, which would usually filter
 240                  * out root/nobody too, hence these checks might appear redundant — but they actually are
 241                  * not, as we want to support environments where /etc/passwd and /etc/group are non-existent,
 242                  * and the user/group databases fully synthesized at runtime. Moreover, the name of the
 243                  * user/group name of the "nobody" account differs between distros, hence a check by numeric
 244                  * UID is safer. */
 245                 if (u->uid == 0 || streq(u->user_name, "root"))
 246                         return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Mapping 'root' user not supported, sorry.");
 247                 if (u->uid == UID_NOBODY || STR_IN_SET(u->user_name, NOBODY_USER_NAME, "nobody"))
 248                         return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Mapping 'nobody' user not supported, sorry.");
 249
 250                 if (u->uid >= uid_shift && u->uid < uid_shift + uid_range)
 251                         return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "UID of user '%s' to map is already in container UID range, refusing.", u->user_name);
 252
 253                 r = groupdb_by_gid(u->gid, USERDB_DONT_SYNTHESIZE, &g);
 254                 if (r < 0)
 255                         return log_error_errno(r, "Failed to resolve group of user '%s': %m", u->user_name);
 256
 257                 if (g->gid >= uid_shift && g->gid < uid_shift + uid_range)
 258                         return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "GID of group '%s' to map is already in container GID range, refusing.", g->group_name);
 259
 260                 /* We want to synthesize exactly one user + group from the host into the container. This only
 261                  * makes sense if the user on the host has its own private group. We can't reasonably check
 262                  * this, so we just check of the name of user and group match.
 263                  *
 264                  * One of these days we might want to support users in a shared/common group too, but it's
 265                  * not clear to me how this would have to be mapped, precisely given that the common group
 266                  * probably already exists in the container. */
 267                 if (!streq(u->user_name, g->group_name))
 268                         return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP),
 269                                                "Sorry, mapping users without private groups is currently not supported.");
 270
 271                 r = find_free_uid(directory, uid_range, &current_uid);
 272                 if (r < 0)
 273                         return r;
 274
 275                 r = convert_user(directory, u, g, current_uid, &cu, &cg);
 276                 if (r < 0)
 277                         return r;
 278
 279                 if (!GREEDY_REALLOC(c->data, c->n_data + 1))
 280                         return log_oom();
 281
 282                 sm = strdup(u->home_directory);
 283                 if (!sm)
 284                         return log_oom();
 285
 286                 sd = strdup(cu->home_directory);
 287                 if (!sd)
 288                         return log_oom();
 289
 290                 cm = reallocarray(*custom_mounts, sizeof(CustomMount), *n_custom_mounts + 1);
 291                 if (!cm)
 292                         return log_oom();
 293
 294                 *custom_mounts = cm;
 295
 296                 (*custom_mounts)[(*n_custom_mounts)++] = (CustomMount) {
 297                         .type = CUSTOM_MOUNT_BIND,
 298                         .source = TAKE_PTR(sm),
 299                         .destination = TAKE_PTR(sd),
 300                 };
 301
 302                 c->data[c->n_data++] = (BindUserData) {
 303                         .host_user = TAKE_PTR(u),
 304                         .host_group = TAKE_PTR(g),
 305                         .payload_user = TAKE_PTR(cu),
 306                         .payload_group = TAKE_PTR(cg),
 307                 };
 308
 309                 current_uid++;
 310         }
 311
 312         *ret = TAKE_PTR(c);
 313         return 1;
 314 }
 315
 316 static int write_and_symlink(
 317                 const char *root,
 318                 JsonVariant *v,
 319                 const char *name,
 320                 uid_t uid,
 321                 const char *suffix,
 322                 WriteStringFileFlags extra_flags) {
 323
 324         _cleanup_free_ char *j = NULL, *f = NULL, *p = NULL, *q = NULL;
 325         int r;
 326
 327         assert(root);
 328         assert(v);
 329         assert(name);
 330         assert(uid_is_valid(uid));
 331         assert(suffix);
 332
 333         r = json_variant_format(v, JSON_FORMAT_NEWLINE, &j);
 334         if (r < 0)
 335                 return log_error_errno(r, "Failed to format user record JSON: %m");
 336
 337         f = strjoin(name, suffix);
 338         if (!f)
 339                 return log_oom();
 340
 341         p = path_join(root, "/run/host/userdb/", f);
 342         if (!p)
 343                 return log_oom();
 344
 345         if (asprintf(&q, "%s/run/host/userdb/" UID_FMT "%s", root, uid, suffix) < 0)
 346                 return log_oom();
 347
 348         if (symlink(f, q) < 0)
 349                 return log_error_errno(errno, "Failed to create symlink '%s': %m", q);
 350
 351         r = userns_lchown(q, 0, 0);
 352         if (r < 0)
 353                 return log_error_errno(r, "Failed to adjust access mode of '%s': %m", q);
 354
 355         r = write_string_file(p, j, WRITE_STRING_FILE_CREATE|extra_flags);
 356         if (r < 0)
 357                 return log_error_errno(r, "Failed to write %s: %m", p);
 358
 359         r = userns_lchown(p, 0, 0);
 360         if (r < 0)
 361                 return log_error_errno(r, "Failed to adjust access mode of '%s': %m", p);
 362
 363         return 0;
 364 }
 365
 366 int bind_user_setup(
 367                 const BindUserContext *c,
 368                 const char *root) {
 369
 370         static const UserRecordLoadFlags strip_flags = /* Removes privileged info */
 371                 USER_RECORD_REQUIRE_REGULAR|
 372                 USER_RECORD_STRIP_PRIVILEGED|
 373                 USER_RECORD_ALLOW_PER_MACHINE|
 374                 USER_RECORD_ALLOW_BINDING|
 375                 USER_RECORD_ALLOW_SIGNATURE|
 376                 USER_RECORD_PERMISSIVE;
 377         static const UserRecordLoadFlags shadow_flags = /* Extracts privileged info */
 378                 USER_RECORD_STRIP_REGULAR|
 379                 USER_RECORD_ALLOW_PRIVILEGED|
 380                 USER_RECORD_STRIP_PER_MACHINE|
 381                 USER_RECORD_STRIP_BINDING|
 382                 USER_RECORD_STRIP_SIGNATURE|
 383                 USER_RECORD_EMPTY_OK|
 384                 USER_RECORD_PERMISSIVE;
 385         int r;
 386
 387         assert(root);
 388
 389         if (!c || c->n_data == 0)
 390                 return 0;
 391
 392         r = userns_mkdir(root, "/run/host", 0755, 0, 0);
 393         if (r < 0)
 394                 return log_error_errno(r, "Failed to create /run/host: %m");
 395
 396         r = userns_mkdir(root, "/run/host/home", 0755, 0, 0);
 397         if (r < 0)
 398                 return log_error_errno(r, "Failed to create /run/host/userdb: %m");
 399
 400         r = userns_mkdir(root, "/run/host/userdb", 0755, 0, 0);
 401         if (r < 0)
 402                 return log_error_errno(r, "Failed to create /run/host/userdb: %m");
 403
 404         for (size_t i = 0; i < c->n_data; i++) {
 405                 _cleanup_(group_record_unrefp) GroupRecord *stripped_group = NULL, *shadow_group = NULL;
 406                 _cleanup_(user_record_unrefp) UserRecord *stripped_user = NULL, *shadow_user = NULL;
 407                 const BindUserData *d = c->data + i;
 408
 409                 /* First, write shadow (i.e. privileged) data for group record */
 410                 r = group_record_clone(d->payload_group, shadow_flags, &shadow_group);
 411                 if (r < 0)
 412                         return log_error_errno(r, "Failed to extract privileged information from group record: %m");
 413
 414                 if (!json_variant_is_blank_object(shadow_group->json)) {
 415                         r = write_and_symlink(
 416                                         root,
 417                                         shadow_group->json,
 418                                         d->payload_group->group_name,
 419                                         d->payload_group->gid,
 420                                         ".group-privileged",
 421                                         WRITE_STRING_FILE_MODE_0600);
 422                         if (r < 0)
 423                                 return r;
 424                 }
 425
 426                 /* Second, write main part of group record. */
 427                 r = group_record_clone(d->payload_group, strip_flags, &stripped_group);
 428                 if (r < 0)
 429                         return log_error_errno(r, "Failed to strip privileged information from group record: %m");
 430
 431                 r = write_and_symlink(
 432                                 root,
 433                                 stripped_group->json,
 434                                 d->payload_group->group_name,
 435                                 d->payload_group->gid,
 436                                 ".group",
 437                                 0);
 438                 if (r < 0)
 439                         return r;
 440
 441                 /* Third, write out user shadow data. i.e. extract privileged info from user record */
 442                 r = user_record_clone(d->payload_user, shadow_flags, &shadow_user);
 443                 if (r < 0)
 444                         return log_error_errno(r, "Failed to extract privileged information from user record: %m");
 445
 446                 if (!json_variant_is_blank_object(shadow_user->json)) {
 447                         r = write_and_symlink(
 448                                         root,
 449                                         shadow_user->json,
 450                                         d->payload_user->user_name,
 451                                         d->payload_user->uid,
 452                                         ".user-privileged",
 453                                         WRITE_STRING_FILE_MODE_0600);
 454                         if (r < 0)
 455                                 return r;
 456                 }
 457
 458                 /* Finally write out the main part of the user record */
 459                 r = user_record_clone(d->payload_user, strip_flags, &stripped_user);
 460                 if (r < 0)
 461                         return log_error_errno(r, "Failed to strip privileged information from user record: %m");
 462
 463                 r = write_and_symlink(
 464                                 root,
 465                                 stripped_user->json,
 466                                 d->payload_user->user_name,
 467                                 d->payload_user->uid,
 468                                 ".user",
 469                                 0);
 470                 if (r < 0)
 471                         return r;
 472         }
 473
 474         return 1;
 475 }