Adding upstream version 241.upstream/241upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

2 files changed, 797 insertions, 0 deletions

diff --git a/src/nss-mymachines/nss-mymachines.c b/src/nss-mymachines/nss-mymachines.c
new file mode 100644
index 0000000..486a658
--- /dev/null
+++ b/src/nss-mymachines/nss-mymachines.c
@@ -0,0 +1,776 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include <netdb.h>
+#include <nss.h>
+
+#include "sd-bus.h"
+#include "sd-login.h"
+
+#include "alloc-util.h"
+#include "bus-common-errors.h"
+#include "env-util.h"
+#include "hostname-util.h"
+#include "in-addr-util.h"
+#include "macro.h"
+#include "nss-util.h"
+#include "signal-util.h"
+#include "string-util.h"
+#include "user-util.h"
+#include "util.h"
+
+NSS_GETHOSTBYNAME_PROTOTYPES(mymachines);
+NSS_GETPW_PROTOTYPES(mymachines);
+NSS_GETGR_PROTOTYPES(mymachines);
+
+#define HOST_UID_LIMIT ((uid_t) UINT32_C(0x10000))
+#define HOST_GID_LIMIT ((gid_t) UINT32_C(0x10000))
+
+static int count_addresses(sd_bus_message *m, int af, unsigned *ret) {
+        unsigned c = 0;
+        int r;
+
+        assert(m);
+        assert(ret);
+
+        while ((r = sd_bus_message_enter_container(m, 'r', "iay")) > 0) {
+                int family;
+
+                r = sd_bus_message_read(m, "i", &family);
+                if (r < 0)
+                        return r;
+
+                r = sd_bus_message_skip(m, "ay");
+                if (r < 0)
+                        return r;
+
+                r = sd_bus_message_exit_container(m);
+                if (r < 0)
+                        return r;
+
+                if (af != AF_UNSPEC && family != af)
+                        continue;
+
+                c++;
+        }
+        if (r < 0)
+                return r;
+
+        r = sd_bus_message_rewind(m, false);
+        if (r < 0)
+                return r;
+
+        *ret = c;
+        return 0;
+}
+
+static bool avoid_deadlock(void) {
+
+        /* Check whether this lookup might have a chance of deadlocking because we are called from the service manager
+         * code activating systemd-machined.service. After all, we shouldn't synchronously do lookups to
+         * systemd-machined if we are required to finish before it can be started. This of course won't detect all
+         * possible dead locks of this kind, but it should work for the most obvious cases. */
+
+        if (geteuid() != 0) /* Ignore the env vars unless we are privileged. */
+                return false;
+
+        return streq_ptr(getenv("SYSTEMD_ACTIVATION_UNIT"), "systemd-machined.service") &&
+               streq_ptr(getenv("SYSTEMD_ACTIVATION_SCOPE"), "system");
+}
+
+enum nss_status _nss_mymachines_gethostbyname4_r(
+                const char *name,
+                struct gaih_addrtuple **pat,
+                char *buffer, size_t buflen,
+                int *errnop, int *h_errnop,
+                int32_t *ttlp) {
+
+        struct gaih_addrtuple *r_tuple, *r_tuple_first = NULL;
+        _cleanup_(sd_bus_message_unrefp) sd_bus_message* reply = NULL;
+        _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
+        _cleanup_free_ int *ifindices = NULL;
+        _cleanup_free_ char *class = NULL;
+        size_t l, ms, idx;
+        unsigned i = 0, c = 0;
+        char *r_name;
+        int n_ifindices, r;
+
+        PROTECT_ERRNO;
+        BLOCK_SIGNALS(NSS_SIGNALS_BLOCK);
+
+        assert(name);
+        assert(pat);
+        assert(buffer);
+        assert(errnop);
+        assert(h_errnop);
+
+        r = sd_machine_get_class(name, &class);
+        if (r < 0)
+                goto fail;
+        if (!streq(class, "container")) {
+                r = -ENOTTY;
+                goto fail;
+        }
+
+        n_ifindices = sd_machine_get_ifindices(name, &ifindices);
+        if (n_ifindices < 0) {
+                r = n_ifindices;
+                goto fail;
+        }
+
+        if (avoid_deadlock()) {
+                r = -EDEADLK;
+                goto fail;
+        }
+
+        r = sd_bus_open_system(&bus);
+        if (r < 0)
+                goto fail;
+
+        r = sd_bus_call_method(bus,
+                               "org.freedesktop.machine1",
+                               "/org/freedesktop/machine1",
+                               "org.freedesktop.machine1.Manager",
+                               "GetMachineAddresses",
+                               NULL,
+                               &reply,
+                               "s", name);
+        if (r < 0)
+                goto fail;
+
+        r = sd_bus_message_enter_container(reply, 'a', "(iay)");
+        if (r < 0)
+                goto fail;
+
+        r = count_addresses(reply, AF_UNSPEC, &c);
+        if (r < 0)
+                goto fail;
+
+        if (c <= 0) {
+                *h_errnop = HOST_NOT_FOUND;
+                return NSS_STATUS_NOTFOUND;
+        }
+
+        l = strlen(name);
+        ms = ALIGN(l+1) + ALIGN(sizeof(struct gaih_addrtuple)) * c;
+        if (buflen < ms) {
+                UNPROTECT_ERRNO;
+                *errnop = ERANGE;
+                *h_errnop = NETDB_INTERNAL;
+                return NSS_STATUS_TRYAGAIN;
+        }
+
+        /* First, append name */
+        r_name = buffer;
+        memcpy(r_name, name, l+1);
+        idx = ALIGN(l+1);
+
+        /* Second, append addresses */
+        r_tuple_first = (struct gaih_addrtuple*) (buffer + idx);
+        while ((r = sd_bus_message_enter_container(reply, 'r', "iay")) > 0) {
+                int family;
+                const void *a;
+                size_t sz;
+
+                r = sd_bus_message_read(reply, "i", &family);
+                if (r < 0)
+                        goto fail;
+
+                r = sd_bus_message_read_array(reply, 'y', &a, &sz);
+                if (r < 0)
+                        goto fail;
+
+                r = sd_bus_message_exit_container(reply);
+                if (r < 0)
+                        goto fail;
+
+                if (!IN_SET(family, AF_INET, AF_INET6)) {
+                        r = -EAFNOSUPPORT;
+                        goto fail;
+                }
+
+                if (sz != FAMILY_ADDRESS_SIZE(family)) {
+                        r = -EINVAL;
+                        goto fail;
+                }
+
+                r_tuple = (struct gaih_addrtuple*) (buffer + idx);
+                r_tuple->next = i == c-1 ? NULL : (struct gaih_addrtuple*) ((char*) r_tuple + ALIGN(sizeof(struct gaih_addrtuple)));
+                r_tuple->name = r_name;
+                r_tuple->family = family;
+                r_tuple->scopeid = n_ifindices == 1 ? ifindices[0] : 0;
+                memcpy(r_tuple->addr, a, sz);
+
+                idx += ALIGN(sizeof(struct gaih_addrtuple));
+                i++;
+        }
+
+        assert(i == c);
+
+        r = sd_bus_message_exit_container(reply);
+        if (r < 0)
+                goto fail;
+
+        assert(idx == ms);
+
+        if (*pat)
+                **pat = *r_tuple_first;
+        else
+                *pat = r_tuple_first;
+
+        if (ttlp)
+                *ttlp = 0;
+
+        /* Explicitly reset both *h_errnop and h_errno to work around
+         * https://bugzilla.redhat.com/show_bug.cgi?id=1125975 */
+        *h_errnop = NETDB_SUCCESS;
+        h_errno = 0;
+
+        return NSS_STATUS_SUCCESS;
+
+fail:
+        UNPROTECT_ERRNO;
+        *errnop = -r;
+        *h_errnop = NO_DATA;
+        return NSS_STATUS_UNAVAIL;
+}
+
+enum nss_status _nss_mymachines_gethostbyname3_r(
+                const char *name,
+                int af,
+                struct hostent *result,
+                char *buffer, size_t buflen,
+                int *errnop, int *h_errnop,
+                int32_t *ttlp,
+                char **canonp) {
+
+        _cleanup_(sd_bus_message_unrefp) sd_bus_message* reply = NULL;
+        _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
+        _cleanup_free_ char *class = NULL;
+        unsigned c = 0, i = 0;
+        char *r_name, *r_aliases, *r_addr, *r_addr_list;
+        size_t l, idx, ms, alen;
+        int r;
+
+        PROTECT_ERRNO;
+        BLOCK_SIGNALS(NSS_SIGNALS_BLOCK);
+
+        assert(name);
+        assert(result);
+        assert(buffer);
+        assert(errnop);
+        assert(h_errnop);
+
+        if (af == AF_UNSPEC)
+                af = AF_INET;
+
+        if (af != AF_INET && af != AF_INET6) {
+                r = -EAFNOSUPPORT;
+                goto fail;
+        }
+
+        r = sd_machine_get_class(name, &class);
+        if (r < 0)
+                goto fail;
+        if (!streq(class, "container")) {
+                r = -ENOTTY;
+                goto fail;
+        }
+
+        if (avoid_deadlock()) {
+                r = -EDEADLK;
+                goto fail;
+        }
+
+        r = sd_bus_open_system(&bus);
+        if (r < 0)
+                goto fail;
+
+        r = sd_bus_call_method(bus,
+                               "org.freedesktop.machine1",
+                               "/org/freedesktop/machine1",
+                               "org.freedesktop.machine1.Manager",
+                               "GetMachineAddresses",
+                               NULL,
+                               &reply,
+                               "s", name);
+        if (r < 0)
+                goto fail;
+
+        r = sd_bus_message_enter_container(reply, 'a', "(iay)");
+        if (r < 0)
+                goto fail;
+
+        r = count_addresses(reply, af, &c);
+        if (r < 0)
+                goto fail;
+
+        if (c <= 0) {
+                *h_errnop = HOST_NOT_FOUND;
+                return NSS_STATUS_NOTFOUND;
+        }
+
+        alen = FAMILY_ADDRESS_SIZE(af);
+        l = strlen(name);
+
+        ms = ALIGN(l+1) + c * ALIGN(alen) + (c+2) * sizeof(char*);
+
+        if (buflen < ms) {
+                UNPROTECT_ERRNO;
+                *errnop = ERANGE;
+                *h_errnop = NETDB_INTERNAL;
+                return NSS_STATUS_TRYAGAIN;
+        }
+
+        /* First, append name */
+        r_name = buffer;
+        memcpy(r_name, name, l+1);
+        idx = ALIGN(l+1);
+
+        /* Second, create aliases array */
+        r_aliases = buffer + idx;
+        ((char**) r_aliases)[0] = NULL;
+        idx += sizeof(char*);
+
+        /* Third, append addresses */
+        r_addr = buffer + idx;
+        while ((r = sd_bus_message_enter_container(reply, 'r', "iay")) > 0) {
+                int family;
+                const void *a;
+                size_t sz;
+
+                r = sd_bus_message_read(reply, "i", &family);
+                if (r < 0)
+                        goto fail;
+
+                r = sd_bus_message_read_array(reply, 'y', &a, &sz);
+                if (r < 0)
+                        goto fail;
+
+                r = sd_bus_message_exit_container(reply);
+                if (r < 0)
+                        goto fail;
+
+                if (family != af)
+                        continue;
+
+                if (sz != alen) {
+                        r = -EINVAL;
+                        goto fail;
+                }
+
+                memcpy(r_addr + i*ALIGN(alen), a, alen);
+                i++;
+        }
+
+        assert(i == c);
+        idx += c * ALIGN(alen);
+
+        r = sd_bus_message_exit_container(reply);
+        if (r < 0)
+                goto fail;
+
+        /* Third, append address pointer array */
+        r_addr_list = buffer + idx;
+        for (i = 0; i < c; i++)
+                ((char**) r_addr_list)[i] = r_addr + i*ALIGN(alen);
+
+        ((char**) r_addr_list)[i] = NULL;
+        idx += (c+1) * sizeof(char*);
+
+        assert(idx == ms);
+
+        result->h_name = r_name;
+        result->h_aliases = (char**) r_aliases;
+        result->h_addrtype = af;
+        result->h_length = alen;
+        result->h_addr_list = (char**) r_addr_list;
+
+        if (ttlp)
+                *ttlp = 0;
+
+        if (canonp)
+                *canonp = r_name;
+
+        /* Explicitly reset both *h_errnop and h_errno to work around
+         * https://bugzilla.redhat.com/show_bug.cgi?id=1125975 */
+        *h_errnop = NETDB_SUCCESS;
+        h_errno = 0;
+
+        return NSS_STATUS_SUCCESS;
+
+fail:
+        UNPROTECT_ERRNO;
+        *errnop = -r;
+        *h_errnop = NO_DATA;
+        return NSS_STATUS_UNAVAIL;
+}
+
+NSS_GETHOSTBYNAME_FALLBACKS(mymachines);
+
+enum nss_status _nss_mymachines_getpwnam_r(
+                const char *name,
+                struct passwd *pwd,
+                char *buffer, size_t buflen,
+                int *errnop) {
+
+        _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
+        _cleanup_(sd_bus_message_unrefp) sd_bus_message* reply = NULL;
+        _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
+        const char *p, *e, *machine;
+        uint32_t mapped;
+        uid_t uid;
+        size_t l;
+        int r;
+
+        PROTECT_ERRNO;
+        BLOCK_SIGNALS(NSS_SIGNALS_BLOCK);
+
+        assert(name);
+        assert(pwd);
+
+        p = startswith(name, "vu-");
+        if (!p)
+                return NSS_STATUS_NOTFOUND;
+
+        e = strrchr(p, '-');
+        if (!e || e == p)
+                return NSS_STATUS_NOTFOUND;
+
+        if (e - p > HOST_NAME_MAX - 1) /* -1 for the last dash */
+                return NSS_STATUS_NOTFOUND;
+
+        r = parse_uid(e + 1, &uid);
+        if (r < 0)
+                return NSS_STATUS_NOTFOUND;
+
+        machine = strndupa(p, e - p);
+        if (!machine_name_is_valid(machine))
+                return NSS_STATUS_NOTFOUND;
+
+        if (getenv_bool_secure("SYSTEMD_NSS_BYPASS_BUS") > 0)
+                /* Make sure we can't deadlock if we are invoked by dbus-daemon. This way, it won't be able to resolve
+                 * these UIDs, but that should be unproblematic as containers should never be able to connect to a bus
+                 * running on the host. */
+                return NSS_STATUS_NOTFOUND;
+
+        if (avoid_deadlock()) {
+                r = -EDEADLK;
+                goto fail;
+        }
+
+        r = sd_bus_open_system(&bus);
+        if (r < 0)
+                goto fail;
+
+        r = sd_bus_call_method(bus,
+                               "org.freedesktop.machine1",
+                               "/org/freedesktop/machine1",
+                               "org.freedesktop.machine1.Manager",
+                               "MapFromMachineUser",
+                               &error,
+                               &reply,
+                               "su",
+                               machine, (uint32_t) uid);
+        if (r < 0) {
+                if (sd_bus_error_has_name(&error, BUS_ERROR_NO_SUCH_USER_MAPPING))
+                        return NSS_STATUS_NOTFOUND;
+
+                goto fail;
+        }
+
+        r = sd_bus_message_read(reply, "u", &mapped);
+        if (r < 0)
+                goto fail;
+
+        /* Refuse to work if the mapped address is in the host UID range, or if there was no mapping at all. */
+        if (mapped < HOST_UID_LIMIT || mapped == uid)
+                return NSS_STATUS_NOTFOUND;
+
+        l = strlen(name);
+        if (buflen < l+1) {
+                UNPROTECT_ERRNO;
+                *errnop = ERANGE;
+                return NSS_STATUS_TRYAGAIN;
+        }
+
+        memcpy(buffer, name, l+1);
+
+        pwd->pw_name = buffer;
+        pwd->pw_uid = mapped;
+        pwd->pw_gid = GID_NOBODY;
+        pwd->pw_gecos = buffer;
+        pwd->pw_passwd = (char*) "*"; /* locked */
+        pwd->pw_dir = (char*) "/";
+        pwd->pw_shell = (char*) "/sbin/nologin";
+
+        return NSS_STATUS_SUCCESS;
+
+fail:
+        UNPROTECT_ERRNO;
+        *errnop = -r;
+        return NSS_STATUS_UNAVAIL;
+}
+
+enum nss_status _nss_mymachines_getpwuid_r(
+                uid_t uid,
+                struct passwd *pwd,
+                char *buffer, size_t buflen,
+                int *errnop) {
+
+        _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
+        _cleanup_(sd_bus_message_unrefp) sd_bus_message* reply = NULL;
+        _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
+        const char *machine;
+        uint32_t mapped;
+        int r;
+
+        PROTECT_ERRNO;
+        BLOCK_SIGNALS(NSS_SIGNALS_BLOCK);
+
+        if (!uid_is_valid(uid))
+                return NSS_STATUS_NOTFOUND;
+
+        /* We consider all uids < 65536 host uids */
+        if (uid < HOST_UID_LIMIT)
+                return NSS_STATUS_NOTFOUND;
+
+        if (getenv_bool_secure("SYSTEMD_NSS_BYPASS_BUS") > 0)
+                return NSS_STATUS_NOTFOUND;
+
+        if (avoid_deadlock()) {
+                r = -EDEADLK;
+                goto fail;
+        }
+
+        r = sd_bus_open_system(&bus);
+        if (r < 0)
+                goto fail;
+
+        r = sd_bus_call_method(bus,
+                               "org.freedesktop.machine1",
+                               "/org/freedesktop/machine1",
+                               "org.freedesktop.machine1.Manager",
+                               "MapToMachineUser",
+                               &error,
+                               &reply,
+                               "u",
+                               (uint32_t) uid);
+        if (r < 0) {
+                if (sd_bus_error_has_name(&error, BUS_ERROR_NO_SUCH_USER_MAPPING))
+                        return NSS_STATUS_NOTFOUND;
+
+                goto fail;
+        }
+
+        r = sd_bus_message_read(reply, "sou", &machine, NULL, &mapped);
+        if (r < 0)
+                goto fail;
+
+        if (mapped == uid)
+                return NSS_STATUS_NOTFOUND;
+
+        if (snprintf(buffer, buflen, "vu-%s-" UID_FMT, machine, (uid_t) mapped) >= (int) buflen) {
+                UNPROTECT_ERRNO;
+                *errnop = ERANGE;
+                return NSS_STATUS_TRYAGAIN;
+        }
+
+        pwd->pw_name = buffer;
+        pwd->pw_uid = uid;
+        pwd->pw_gid = GID_NOBODY;
+        pwd->pw_gecos = buffer;
+        pwd->pw_passwd = (char*) "*"; /* locked */
+        pwd->pw_dir = (char*) "/";
+        pwd->pw_shell = (char*) "/sbin/nologin";
+
+        return NSS_STATUS_SUCCESS;
+
+fail:
+        UNPROTECT_ERRNO;
+        *errnop = -r;
+        return NSS_STATUS_UNAVAIL;
+}
+
+#pragma GCC diagnostic ignored "-Wsizeof-pointer-memaccess"
+
+enum nss_status _nss_mymachines_getgrnam_r(
+                const char *name,
+                struct group *gr,
+                char *buffer, size_t buflen,
+                int *errnop) {
+
+        _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
+        _cleanup_(sd_bus_message_unrefp) sd_bus_message* reply = NULL;
+        _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
+        const char *p, *e, *machine;
+        uint32_t mapped;
+        uid_t gid;
+        size_t l;
+        int r;
+
+        PROTECT_ERRNO;
+        BLOCK_SIGNALS(NSS_SIGNALS_BLOCK);
+
+        assert(name);
+        assert(gr);
+
+        p = startswith(name, "vg-");
+        if (!p)
+                return NSS_STATUS_NOTFOUND;
+
+        e = strrchr(p, '-');
+        if (!e || e == p)
+                return NSS_STATUS_NOTFOUND;
+
+        if (e - p > HOST_NAME_MAX - 1)  /* -1 for the last dash */
+                return NSS_STATUS_NOTFOUND;
+
+        r = parse_gid(e + 1, &gid);
+        if (r < 0)
+                return NSS_STATUS_NOTFOUND;
+
+        machine = strndupa(p, e - p);
+        if (!machine_name_is_valid(machine))
+                return NSS_STATUS_NOTFOUND;
+
+        if (getenv_bool_secure("SYSTEMD_NSS_BYPASS_BUS") > 0)
+                return NSS_STATUS_NOTFOUND;
+
+        if (avoid_deadlock()) {
+                r = -EDEADLK;
+                goto fail;
+        }
+
+        r = sd_bus_open_system(&bus);
+        if (r < 0)
+                goto fail;
+
+        r = sd_bus_call_method(bus,
+                               "org.freedesktop.machine1",
+                               "/org/freedesktop/machine1",
+                               "org.freedesktop.machine1.Manager",
+                               "MapFromMachineGroup",
+                               &error,
+                               &reply,
+                               "su",
+                               machine, (uint32_t) gid);
+        if (r < 0) {
+                if (sd_bus_error_has_name(&error, BUS_ERROR_NO_SUCH_GROUP_MAPPING))
+                        return NSS_STATUS_NOTFOUND;
+
+                goto fail;
+        }
+
+        r = sd_bus_message_read(reply, "u", &mapped);
+        if (r < 0)
+                goto fail;
+
+        if (mapped < HOST_GID_LIMIT || mapped == gid)
+                return NSS_STATUS_NOTFOUND;
+
+        l = sizeof(char*) + strlen(name) + 1;
+        if (buflen < l) {
+                UNPROTECT_ERRNO;
+                *errnop = ERANGE;
+                return NSS_STATUS_TRYAGAIN;
+        }
+
+        memzero(buffer, sizeof(char*));
+        strcpy(buffer + sizeof(char*), name);
+
+        gr->gr_name = buffer + sizeof(char*);
+        gr->gr_gid = mapped;
+        gr->gr_passwd = (char*) "*"; /* locked */
+        gr->gr_mem = (char**) buffer;
+
+        return NSS_STATUS_SUCCESS;
+
+fail:
+        UNPROTECT_ERRNO;
+        *errnop = -r;
+        return NSS_STATUS_UNAVAIL;
+}
+
+enum nss_status _nss_mymachines_getgrgid_r(
+                gid_t gid,
+                struct group *gr,
+                char *buffer, size_t buflen,
+                int *errnop) {
+
+        _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
+        _cleanup_(sd_bus_message_unrefp) sd_bus_message* reply = NULL;
+        _cleanup_(sd_bus_flush_close_unrefp) sd_bus *bus = NULL;
+        const char *machine;
+        uint32_t mapped;
+        int r;
+
+        PROTECT_ERRNO;
+        BLOCK_SIGNALS(NSS_SIGNALS_BLOCK);
+
+        if (!gid_is_valid(gid))
+                return NSS_STATUS_NOTFOUND;
+
+        /* We consider all gids < 65536 host gids */
+        if (gid < HOST_GID_LIMIT)
+                return NSS_STATUS_NOTFOUND;
+
+        if (getenv_bool_secure("SYSTEMD_NSS_BYPASS_BUS") > 0)
+                return NSS_STATUS_NOTFOUND;
+
+        if (avoid_deadlock()) {
+                r = -EDEADLK;
+                goto fail;
+        }
+
+        r = sd_bus_open_system(&bus);
+        if (r < 0)
+                goto fail;
+
+        r = sd_bus_call_method(bus,
+                               "org.freedesktop.machine1",
+                               "/org/freedesktop/machine1",
+                               "org.freedesktop.machine1.Manager",
+                               "MapToMachineGroup",
+                               &error,
+                               &reply,
+                               "u",
+                               (uint32_t) gid);
+        if (r < 0) {
+                if (sd_bus_error_has_name(&error, BUS_ERROR_NO_SUCH_GROUP_MAPPING))
+                        return NSS_STATUS_NOTFOUND;
+
+                goto fail;
+        }
+
+        r = sd_bus_message_read(reply, "sou", &machine, NULL, &mapped);
+        if (r < 0)
+                goto fail;
+
+        if (mapped == gid)
+                return NSS_STATUS_NOTFOUND;
+
+        if (buflen < sizeof(char*) + 1) {
+                UNPROTECT_ERRNO;
+                *errnop = ERANGE;
+                return NSS_STATUS_TRYAGAIN;
+        }
+
+        memzero(buffer, sizeof(char*));
+        if (snprintf(buffer + sizeof(char*), buflen - sizeof(char*), "vg-%s-" GID_FMT, machine, (gid_t) mapped) >= (int) buflen) {
+                UNPROTECT_ERRNO;
+                *errnop = ERANGE;
+                return NSS_STATUS_TRYAGAIN;
+        }
+
+        gr->gr_name = buffer + sizeof(char*);
+        gr->gr_gid = gid;
+        gr->gr_passwd = (char*) "*"; /* locked */
+        gr->gr_mem = (char**) buffer;
+
+        return NSS_STATUS_SUCCESS;
+
+fail:
+        UNPROTECT_ERRNO;
+        *errnop = -r;
+        return NSS_STATUS_UNAVAIL;
+}
diff --git a/src/nss-mymachines/nss-mymachines.sym b/src/nss-mymachines/nss-mymachines.sym
new file mode 100644
index 0000000..ade6447
--- /dev/null
+++ b/src/nss-mymachines/nss-mymachines.sym
@@ -0,0 +1,21 @@
+/***
+  SPDX-License-Identifier: LGPL-2.1+
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+***/
+
+{
+global:
+        _nss_mymachines_gethostbyname_r;
+        _nss_mymachines_gethostbyname2_r;
+        _nss_mymachines_gethostbyname3_r;
+        _nss_mymachines_gethostbyname4_r;
+        _nss_mymachines_getpwnam_r;
+        _nss_mymachines_getpwuid_r;
+        _nss_mymachines_getgrnam_r;
+        _nss_mymachines_getgrgid_r;
+local: *;
+};