diff options
Diffstat (limited to 'src/nspawn/nspawn-bind-user.c')
| -rw-r--r-- | src/nspawn/nspawn-bind-user.c | 474 |
1 files changed, 474 insertions, 0 deletions
diff --git a/src/nspawn/nspawn-bind-user.c b/src/nspawn/nspawn-bind-user.c new file mode 100644 index 0000000..7a7a19f --- /dev/null +++ b/src/nspawn/nspawn-bind-user.c @@ -0,0 +1,474 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ + +#include "chase-symlinks.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_symlinks_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_symlinks_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; +} |