/* SPDX-License-Identifier: LGPL-2.1-or-later */ #include "chase.h" #include "fd-util.h" #include "fileio.h" #include "format-util.h" #include "nspawn-bind-user.h" #include "nspawn.h" #include "path-util.h" #include "user-util.h" #include "userdb.h" static int check_etc_passwd_collisions( const char *directory, const char *name, uid_t uid) { _cleanup_fclose_ FILE *f = NULL; int r; assert(directory); assert(name || uid_is_valid(uid)); r = chase_and_fopen_unlocked("/etc/passwd", directory, CHASE_PREFIX_ROOT, "re", NULL, &f); if (r == -ENOENT) return 0; /* no user database? then no user, hence no collision */ if (r < 0) return log_error_errno(r, "Failed to open /etc/passwd of container: %m"); for (;;) { struct passwd *pw; r = fgetpwent_sane(f, &pw); if (r < 0) return log_error_errno(r, "Failed to iterate through /etc/passwd of container: %m"); if (r == 0) /* EOF */ return 0; /* no collision */ if (name && streq_ptr(pw->pw_name, name)) return 1; /* name collision */ if (uid_is_valid(uid) && pw->pw_uid == uid) return 1; /* UID collision */ } } static int check_etc_group_collisions( const char *directory, const char *name, gid_t gid) { _cleanup_fclose_ FILE *f = NULL; int r; assert(directory); assert(name || gid_is_valid(gid)); r = chase_and_fopen_unlocked("/etc/group", directory, CHASE_PREFIX_ROOT, "re", NULL, &f); if (r == -ENOENT) return 0; /* no group database? then no group, hence no collision */ if (r < 0) return log_error_errno(r, "Failed to open /etc/group of container: %m"); for (;;) { struct group *gr; r = fgetgrent_sane(f, &gr); if (r < 0) return log_error_errno(r, "Failed to iterate through /etc/group of container: %m"); if (r == 0) return 0; /* no collision */ if (name && streq_ptr(gr->gr_name, name)) return 1; /* name collision */ if (gid_is_valid(gid) && gr->gr_gid == gid) return 1; /* gid collision */ } } static int convert_user( const char *directory, UserRecord *u, GroupRecord *g, uid_t allocate_uid, UserRecord **ret_converted_user, GroupRecord **ret_converted_group) { _cleanup_(group_record_unrefp) GroupRecord *converted_group = NULL; _cleanup_(user_record_unrefp) UserRecord *converted_user = NULL; _cleanup_free_ char *h = NULL; JsonVariant *p, *hp = NULL; int r; assert(u); assert(g); assert(u->gid == g->gid); r = check_etc_passwd_collisions(directory, u->user_name, UID_INVALID); if (r < 0) return r; if (r > 0) return log_error_errno(SYNTHETIC_ERRNO(EBUSY), "Sorry, the user '%s' already exists in the container.", u->user_name); r = check_etc_group_collisions(directory, g->group_name, GID_INVALID); if (r < 0) return r; if (r > 0) return log_error_errno(SYNTHETIC_ERRNO(EBUSY), "Sorry, the group '%s' already exists in the container.", g->group_name); h = path_join("/run/host/home/", u->user_name); if (!h) return log_oom(); /* Acquire the source hashed password array as-is, so that it retains the JSON_VARIANT_SENSITIVE flag */ p = json_variant_by_key(u->json, "privileged"); if (p) hp = json_variant_by_key(p, "hashedPassword"); r = user_record_build( &converted_user, JSON_BUILD_OBJECT( JSON_BUILD_PAIR("userName", JSON_BUILD_STRING(u->user_name)), JSON_BUILD_PAIR("uid", JSON_BUILD_UNSIGNED(allocate_uid)), JSON_BUILD_PAIR("gid", JSON_BUILD_UNSIGNED(allocate_uid)), JSON_BUILD_PAIR_CONDITION(u->disposition >= 0, "disposition", JSON_BUILD_STRING(user_disposition_to_string(u->disposition))), JSON_BUILD_PAIR("homeDirectory", JSON_BUILD_STRING(h)), JSON_BUILD_PAIR("service", JSON_BUILD_CONST_STRING("io.systemd.NSpawn")), JSON_BUILD_PAIR_CONDITION(!strv_isempty(u->hashed_password), "privileged", JSON_BUILD_OBJECT( JSON_BUILD_PAIR("hashedPassword", JSON_BUILD_VARIANT(hp)))))); if (r < 0) return log_error_errno(r, "Failed to build container user record: %m"); r = group_record_build( &converted_group, JSON_BUILD_OBJECT( JSON_BUILD_PAIR("groupName", JSON_BUILD_STRING(g->group_name)), JSON_BUILD_PAIR("gid", JSON_BUILD_UNSIGNED(allocate_uid)), JSON_BUILD_PAIR_CONDITION(g->disposition >= 0, "disposition", JSON_BUILD_STRING(user_disposition_to_string(g->disposition))), JSON_BUILD_PAIR("service", JSON_BUILD_CONST_STRING("io.systemd.NSpawn")))); if (r < 0) return log_error_errno(r, "Failed to build container group record: %m"); *ret_converted_user = TAKE_PTR(converted_user); *ret_converted_group = TAKE_PTR(converted_group); return 0; } static int find_free_uid(const char *directory, uid_t max_uid, uid_t *current_uid) { int r; assert(directory); assert(current_uid); for (;; (*current_uid) ++) { if (*current_uid > MAP_UID_MAX || *current_uid > max_uid) return log_error_errno( SYNTHETIC_ERRNO(EBUSY), "No suitable available UID in range " UID_FMT "…" UID_FMT " in container detected, can't map user.", MAP_UID_MIN, MAP_UID_MAX); r = check_etc_passwd_collisions(directory, NULL, *current_uid); if (r < 0) return r; if (r > 0) /* already used */ continue; /* We want to use the UID also as GID, hence check for it in /etc/group too */ r = check_etc_group_collisions(directory, NULL, (gid_t) *current_uid); if (r <= 0) return r; } } BindUserContext* bind_user_context_free(BindUserContext *c) { if (!c) return NULL; assert(c->n_data == 0 || c->data); for (size_t i = 0; i < c->n_data; i++) { user_record_unref(c->data[i].host_user); group_record_unref(c->data[i].host_group); user_record_unref(c->data[i].payload_user); group_record_unref(c->data[i].payload_group); } return mfree(c); } int bind_user_prepare( const char *directory, char **bind_user, uid_t uid_shift, uid_t uid_range, CustomMount **custom_mounts, size_t *n_custom_mounts, BindUserContext **ret) { _cleanup_(bind_user_context_freep) BindUserContext *c = NULL; uid_t current_uid = MAP_UID_MIN; int r; assert(custom_mounts); assert(n_custom_mounts); assert(ret); /* This resolves the users specified in 'bind_user', generates a minimalized JSON user + group record * for it to stick in the container, allocates a UID/GID for it, and updates the custom mount table, * to include an appropriate bind mount mapping. * * This extends the passed custom_mounts/n_custom_mounts with the home directories, and allocates a * new BindUserContext for the user records */ if (strv_isempty(bind_user)) { *ret = NULL; return 0; } c = new0(BindUserContext, 1); if (!c) return log_oom(); STRV_FOREACH(n, bind_user) { _cleanup_(user_record_unrefp) UserRecord *u = NULL, *cu = NULL; _cleanup_(group_record_unrefp) GroupRecord *g = NULL, *cg = NULL; _cleanup_free_ char *sm = NULL, *sd = NULL; CustomMount *cm; r = userdb_by_name(*n, USERDB_DONT_SYNTHESIZE, &u); if (r < 0) return log_error_errno(r, "Failed to resolve user '%s': %m", *n); /* For now, let's refuse mapping the root/nobody users explicitly. The records we generate * are strictly additive, nss-systemd is typically placed last in /etc/nsswitch.conf. Thus * even if we wanted, we couldn't override the root or nobody user records. Note we also * check for name conflicts in /etc/passwd + /etc/group later on, which would usually filter * out root/nobody too, hence these checks might appear redundant — but they actually are * not, as we want to support environments where /etc/passwd and /etc/group are non-existent, * and the user/group databases fully synthesized at runtime. Moreover, the name of the * user/group name of the "nobody" account differs between distros, hence a check by numeric * UID is safer. */ if (u->uid == 0 || streq(u->user_name, "root")) return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Mapping 'root' user not supported, sorry."); if (u->uid == UID_NOBODY || STR_IN_SET(u->user_name, NOBODY_USER_NAME, "nobody")) return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Mapping 'nobody' user not supported, sorry."); if (u->uid >= uid_shift && u->uid < uid_shift + uid_range) return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "UID of user '%s' to map is already in container UID range, refusing.", u->user_name); r = groupdb_by_gid(u->gid, USERDB_DONT_SYNTHESIZE, &g); if (r < 0) return log_error_errno(r, "Failed to resolve group of user '%s': %m", u->user_name); if (g->gid >= uid_shift && g->gid < uid_shift + uid_range) return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "GID of group '%s' to map is already in container GID range, refusing.", g->group_name); /* We want to synthesize exactly one user + group from the host into the container. This only * makes sense if the user on the host has its own private group. We can't reasonably check * this, so we just check of the name of user and group match. * * One of these days we might want to support users in a shared/common group too, but it's * not clear to me how this would have to be mapped, precisely given that the common group * probably already exists in the container. */ if (!streq(u->user_name, g->group_name)) return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "Sorry, mapping users without private groups is currently not supported."); r = find_free_uid(directory, uid_range, ¤t_uid); if (r < 0) return r; r = convert_user(directory, u, g, current_uid, &cu, &cg); if (r < 0) return r; if (!GREEDY_REALLOC(c->data, c->n_data + 1)) return log_oom(); sm = strdup(u->home_directory); if (!sm) return log_oom(); sd = strdup(cu->home_directory); if (!sd) return log_oom(); cm = reallocarray(*custom_mounts, *n_custom_mounts + 1, sizeof(CustomMount)); if (!cm) return log_oom(); *custom_mounts = cm; (*custom_mounts)[(*n_custom_mounts)++] = (CustomMount) { .type = CUSTOM_MOUNT_BIND, .source = TAKE_PTR(sm), .destination = TAKE_PTR(sd), }; c->data[c->n_data++] = (BindUserData) { .host_user = TAKE_PTR(u), .host_group = TAKE_PTR(g), .payload_user = TAKE_PTR(cu), .payload_group = TAKE_PTR(cg), }; current_uid++; } *ret = TAKE_PTR(c); return 1; } static int write_and_symlink( const char *root, JsonVariant *v, const char *name, uid_t uid, const char *suffix, WriteStringFileFlags extra_flags) { _cleanup_free_ char *j = NULL, *f = NULL, *p = NULL, *q = NULL; int r; assert(root); assert(v); assert(name); assert(uid_is_valid(uid)); assert(suffix); r = json_variant_format(v, JSON_FORMAT_NEWLINE, &j); if (r < 0) return log_error_errno(r, "Failed to format user record JSON: %m"); f = strjoin(name, suffix); if (!f) return log_oom(); p = path_join(root, "/run/host/userdb/", f); if (!p) return log_oom(); if (asprintf(&q, "%s/run/host/userdb/" UID_FMT "%s", root, uid, suffix) < 0) return log_oom(); if (symlink(f, q) < 0) return log_error_errno(errno, "Failed to create symlink '%s': %m", q); r = userns_lchown(q, 0, 0); if (r < 0) return log_error_errno(r, "Failed to adjust access mode of '%s': %m", q); r = write_string_file(p, j, WRITE_STRING_FILE_CREATE|extra_flags); if (r < 0) return log_error_errno(r, "Failed to write %s: %m", p); r = userns_lchown(p, 0, 0); if (r < 0) return log_error_errno(r, "Failed to adjust access mode of '%s': %m", p); return 0; } int bind_user_setup( const BindUserContext *c, const char *root) { static const UserRecordLoadFlags strip_flags = /* Removes privileged info */ USER_RECORD_REQUIRE_REGULAR| USER_RECORD_STRIP_PRIVILEGED| USER_RECORD_ALLOW_PER_MACHINE| USER_RECORD_ALLOW_BINDING| USER_RECORD_ALLOW_SIGNATURE| USER_RECORD_PERMISSIVE; static const UserRecordLoadFlags shadow_flags = /* Extracts privileged info */ USER_RECORD_STRIP_REGULAR| USER_RECORD_ALLOW_PRIVILEGED| USER_RECORD_STRIP_PER_MACHINE| USER_RECORD_STRIP_BINDING| USER_RECORD_STRIP_SIGNATURE| USER_RECORD_EMPTY_OK| USER_RECORD_PERMISSIVE; int r; assert(root); if (!c || c->n_data == 0) return 0; r = userns_mkdir(root, "/run/host", 0755, 0, 0); if (r < 0) return log_error_errno(r, "Failed to create /run/host: %m"); r = userns_mkdir(root, "/run/host/home", 0755, 0, 0); if (r < 0) return log_error_errno(r, "Failed to create /run/host/home: %m"); r = userns_mkdir(root, "/run/host/userdb", 0755, 0, 0); if (r < 0) return log_error_errno(r, "Failed to create /run/host/userdb: %m"); for (size_t i = 0; i < c->n_data; i++) { _cleanup_(group_record_unrefp) GroupRecord *stripped_group = NULL, *shadow_group = NULL; _cleanup_(user_record_unrefp) UserRecord *stripped_user = NULL, *shadow_user = NULL; const BindUserData *d = c->data + i; /* First, write shadow (i.e. privileged) data for group record */ r = group_record_clone(d->payload_group, shadow_flags, &shadow_group); if (r < 0) return log_error_errno(r, "Failed to extract privileged information from group record: %m"); if (!json_variant_is_blank_object(shadow_group->json)) { r = write_and_symlink( root, shadow_group->json, d->payload_group->group_name, d->payload_group->gid, ".group-privileged", WRITE_STRING_FILE_MODE_0600); if (r < 0) return r; } /* Second, write main part of group record. */ r = group_record_clone(d->payload_group, strip_flags, &stripped_group); if (r < 0) return log_error_errno(r, "Failed to strip privileged information from group record: %m"); r = write_and_symlink( root, stripped_group->json, d->payload_group->group_name, d->payload_group->gid, ".group", 0); if (r < 0) return r; /* Third, write out user shadow data. i.e. extract privileged info from user record */ r = user_record_clone(d->payload_user, shadow_flags, &shadow_user); if (r < 0) return log_error_errno(r, "Failed to extract privileged information from user record: %m"); if (!json_variant_is_blank_object(shadow_user->json)) { r = write_and_symlink( root, shadow_user->json, d->payload_user->user_name, d->payload_user->uid, ".user-privileged", WRITE_STRING_FILE_MODE_0600); if (r < 0) return r; } /* Finally write out the main part of the user record */ r = user_record_clone(d->payload_user, strip_flags, &stripped_user); if (r < 0) return log_error_errno(r, "Failed to strip privileged information from user record: %m"); r = write_and_symlink( root, stripped_user->json, d->payload_user->user_name, d->payload_user->uid, ".user", 0); if (r < 0) return r; } return 1; }