core/mount: comprehensively disable mount unit support if no libmount (#39884)

src/basic/dlfcn-util.c

@@ -84,6 +84,7 @@ void block_dlopen(void) {
 }
 
 int dlopen_safe(const char *filename, void **ret, const char **reterr_dlerror) {
+        _cleanup_(dlclosep) void *dl = NULL;
         int r;
 
         assert(filename);
@@ -99,8 +100,8 @@ int dlopen_safe(const char *filename, void **ret, const char **reterr_dlerror) {
                 flags |= RTLD_NOLOAD;
 
         errno = 0;
-        void *p = dlopen(filename, flags);
-        if (!p) {
+        dl = dlopen(filename, flags);
+        if (!dl) {
                 if (dlopen_blocked) {
                         (void) dlerror(); /* consume error, so that no later call will return it */
 
@@ -121,7 +122,7 @@ int dlopen_safe(const char *filename, void **ret, const char **reterr_dlerror) {
         }
 
         if (ret)
-                *ret = TAKE_PTR(p);
+                *ret = TAKE_PTR(dl);
 
         return 0;
 }

src/core/automount.c

@@ -1033,6 +1033,9 @@ static void automount_reset_failed(Unit *u) {
 static bool automount_supported(void) {
         static int supported = -1;
 
+        if (!unit_type_supported(UNIT_MOUNT))
+                return false;
+
         if (supported < 0)
                 supported = access("/dev/autofs", F_OK) >= 0;
 

src/core/main.c

@@ -59,7 +59,6 @@
 #include "killall.h"
 #include "kmod-setup.h"
 #include "label-util.h"
-#include "libmount-util.h"
 #include "limits-util.h"
 #include "load-fragment.h"
 #include "log.h"
@@ -3311,12 +3310,6 @@ int main(int argc, char *argv[]) {
                 goto finish;
         }
 
-        r = dlopen_libmount();
-        if (r < 0) {
-                error_message = "Failed to load libmount.so";
-                goto finish;
-        }
-
         r = initialize_runtime(skip_setup,
                                first_boot,
                                &saved_rlimit_nofile,

src/core/meson.build

@@ -202,7 +202,6 @@ executables += [
                 'dependencies' : [
                         libapparmor_cflags,
                         libkmod_cflags,
-                        libmount_cflags,
                         libseccomp_cflags,
                         libselinux_cflags,
                 ],

src/core/mount.c

@@ -240,34 +240,6 @@ static void mount_done(Unit *u) {
         m->timer_event_source = sd_event_source_disable_unref(m->timer_event_source);
 }
 
-static int update_parameters_proc_self_mountinfo(
-                Mount *m,
-                const char *what,
-                const char *options,
-                const char *fstype) {
-
-        MountParameters *p;
-        int r, q, w;
-
-        assert(m);
-
-        p = &m->parameters_proc_self_mountinfo;
-
-        r = free_and_strdup(&p->what, what);
-        if (r < 0)
-                return r;
-
-        q = free_and_strdup(&p->options, options);
-        if (q < 0)
-                return q;
-
-        w = free_and_strdup(&p->fstype, fstype);
-        if (w < 0)
-                return w;
-
-        return r > 0 || q > 0 || w > 0;
-}
-
 static int mount_add_mount_dependencies(Mount *m) {
         MountParameters *pm;
         int r;
@@ -1747,6 +1719,34 @@ static int mount_dispatch_timer(sd_event_source *source, usec_t usec, void *user
 }
 
 #if HAVE_LIBMOUNT
+static int update_parameters_proc_self_mountinfo(
+                Mount *m,
+                const char *what,
+                const char *options,
+                const char *fstype) {
+
+        MountParameters *p;
+        int r, q, w;
+
+        assert(m);
+
+        p = &m->parameters_proc_self_mountinfo;
+
+        r = free_and_strdup(&p->what, what);
+        if (r < 0)
+                return r;
+
+        q = free_and_strdup(&p->options, options);
+        if (q < 0)
+                return q;
+
+        w = free_and_strdup(&p->fstype, fstype);
+        if (w < 0)
+                return w;
+
+        return r > 0 || q > 0 || w > 0;
+}
+
 static int mount_setup_new_unit(
                 Manager *m,
                 const char *name,
@@ -1927,10 +1927,8 @@ static int mount_setup_unit(
 
         return 0;
 }
-#endif
 
 static int mount_load_proc_self_mountinfo(Manager *m, bool set_flags) {
-#if HAVE_LIBMOUNT
         _cleanup_(mnt_free_tablep) struct libmnt_table *table = NULL;
         _cleanup_(mnt_free_iterp) struct libmnt_iter *iter = NULL;
         _cleanup_set_free_ Set *devices = NULL;
@@ -1970,10 +1968,8 @@ static int mount_load_proc_self_mountinfo(Manager *m, bool set_flags) {
         }
 
         return 0;
-#else
-        return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "libmount support not compiled in");
-#endif
 }
+#endif
 
 static void mount_shutdown(Manager *m) {
         assert(m);
@@ -2025,6 +2021,7 @@ static void mount_enumerate_perpetual(Manager *m) {
         int r;
 
         assert(m);
+        assert(unit_type_supported(UNIT_MOUNT));
 
         /* Whatever happens, we know for sure that the root directory is around, and cannot go away. Let's
          * unconditionally synthesize it here and mark it as perpetual. */
@@ -2044,13 +2041,13 @@ static void mount_enumerate_perpetual(Manager *m) {
         unit_add_to_dbus_queue(u);
 }
 
+#if HAVE_LIBMOUNT
 static bool mount_is_mounted(Mount *m) {
         assert(m);
 
         return UNIT(m)->perpetual || FLAGS_SET(m->proc_flags, MOUNT_PROC_IS_MOUNTED);
 }
 
-#if HAVE_LIBMOUNT
 static int mount_on_ratelimit_expire(sd_event_source *s, void *userdata) {
         Manager *m = ASSERT_PTR(userdata);
         Job *j;
@@ -2072,17 +2069,12 @@ static int mount_on_ratelimit_expire(sd_event_source *s, void *userdata) {
 #endif
 
 static void mount_enumerate(Manager *m) {
+        assert(m);
+        assert(unit_type_supported(UNIT_MOUNT));
+
 #if HAVE_LIBMOUNT
         int r;
 
-        assert(m);
-
-        r = dlopen_libmount();
-        if (r < 0) {
-                log_error_errno(r, "Cannot enumerate mounts, as libmount is not available: %m");
-                goto fail;
-        }
-
         sym_mnt_init_debug(0);
 
         if (!m->mount_monitor) {
@@ -2164,23 +2156,20 @@ static void mount_enumerate(Manager *m) {
         return;
 
 fail:
-        mount_shutdown(m);
-#else
-        log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "Cannot enumerate mounts, as libmount support is not compiled in");
-        mount_shutdown(m);
 #endif
+        mount_shutdown(m);
 }
 
 static int drain_libmount(Manager *m) {
-#if HAVE_LIBMOUNT
-        bool rescan = false;
-        int r;
-
         assert(m);
 
         if (!m->mount_monitor)
                 return false;
 
+#if HAVE_LIBMOUNT
+        bool rescan = false;
+        int r;
+
         /* Drain all events and verify that the event is valid.
          *
          * Note that libmount also monitors /run/mount mkdir if the directory does not exist yet. The mkdir
@@ -2196,14 +2185,13 @@ static int drain_libmount(Manager *m) {
         } while (r == 0);
 
         return rescan;
+
 #else
-        return 0;
+        assert_not_reached();
 #endif
 }
 
 static int mount_process_proc_self_mountinfo(Manager *m) {
-        _cleanup_set_free_ Set *around = NULL, *gone = NULL;
-        const char *what;
         int r;
 
         assert(m);
@@ -2212,6 +2200,7 @@ static int mount_process_proc_self_mountinfo(Manager *m) {
         if (r <= 0)
                 return r;
 
+#if HAVE_LIBMOUNT
         r = mount_load_proc_self_mountinfo(m, true);
         if (r < 0) {
                 /* Reset flags, just in case, for later calls */
@@ -2223,6 +2212,8 @@ static int mount_process_proc_self_mountinfo(Manager *m) {
 
         manager_dispatch_load_queue(m);
 
+        _cleanup_set_free_ Set *around = NULL, *gone = NULL;
+
         LIST_FOREACH(units_by_type, u, m->units_by_type[UNIT_MOUNT]) {
                 Mount *mount = MOUNT(u);
 
@@ -2302,6 +2293,7 @@ static int mount_process_proc_self_mountinfo(Manager *m) {
                 mount->proc_flags = 0;
         }
 
+        const char *what;
         SET_FOREACH(what, gone) {
                 if (set_contains(around, what))
                         continue;
@@ -2311,6 +2303,9 @@ static int mount_process_proc_self_mountinfo(Manager *m) {
         }
 
         return 0;
+#else
+        assert_not_reached();
+#endif
 }
 
 #if HAVE_LIBMOUNT
@@ -2410,6 +2405,10 @@ static int mount_test_startable(Unit *u) {
         return true;
 }
 
+static bool mount_supported(void) {
+        return dlopen_libmount() >= 0;
+}
+
 static int mount_subsystem_ratelimited(Manager *m) {
         assert(m);
 
@@ -2554,6 +2553,7 @@ const UnitVTable mount_vtable = {
         .enumerate_perpetual = mount_enumerate_perpetual,
         .enumerate = mount_enumerate,
         .shutdown = mount_shutdown,
+        .supported = mount_supported,
         .subsystem_ratelimited = mount_subsystem_ratelimited,
 
         .status_message_formats = {

src/core/unit.c

@@ -5023,6 +5023,11 @@ int unit_add_mounts_for(Unit *u, const char *path, UnitDependencyMask mask, Unit
         if (hashmap_contains(*unit_map, path)) /* Exit quickly if the path is already covered. */
                 return 0;
 
+        if (!unit_type_supported(UNIT_MOUNT)) {
+                log_once(LOG_NOTICE, "Mount unit not supported, skipping *MountsFor= dependencies.");
+                return 0;
+        }
+
         /* Use the canonical form of the path as the stored key. We call path_is_normalized()
          * only after simplification, since path_is_normalized() rejects paths with '.'.
          * path_is_normalized() also verifies that the path fits in PATH_MAX. */

src/shared/libmount-util.c

@@ -1,11 +1,9 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 
-#include "libmount-util.h"
-
-#if HAVE_LIBMOUNT
 #include <stdio.h>
 
 #include "fstab-util.h"
+#include "libmount-util.h"
 #include "log.h"
 
 static void *libmount_dl = NULL;
@@ -41,10 +39,8 @@ DLSYM_PROTOTYPE(mnt_table_parse_mtab) = NULL;
 DLSYM_PROTOTYPE(mnt_table_parse_stream) = NULL;
 DLSYM_PROTOTYPE(mnt_table_parse_swaps) = NULL;
 DLSYM_PROTOTYPE(mnt_unref_monitor) = NULL;
-#endif
 
 int dlopen_libmount(void) {
-#if HAVE_LIBMOUNT
         ELF_NOTE_DLOPEN("mount",
                         "Support for mount enumeration",
                         ELF_NOTE_DLOPEN_PRIORITY_RECOMMENDED,
@@ -85,12 +81,8 @@ int dlopen_libmount(void) {
                         DLSYM_ARG(mnt_table_parse_stream),
                         DLSYM_ARG(mnt_table_parse_swaps),
                         DLSYM_ARG(mnt_unref_monitor));
-#else
-        return -EOPNOTSUPP;
-#endif
 }
 
-#if HAVE_LIBMOUNT
 int libmount_parse_full(
                 const char *path,
                 FILE *source,
@@ -159,4 +151,3 @@ int libmount_is_leaf(
 
         return r == 1;
 }
-#endif

src/shared/libmount-util.h

@@ -42,6 +42,8 @@ extern DLSYM_PROTOTYPE(mnt_table_parse_stream);
 extern DLSYM_PROTOTYPE(mnt_table_parse_swaps);
 extern DLSYM_PROTOTYPE(mnt_unref_monitor);
 
+int dlopen_libmount(void);
+
 DEFINE_TRIVIAL_CLEANUP_FUNC_FULL_RENAME(struct libmnt_table*, sym_mnt_free_table, mnt_free_tablep, NULL);
 DEFINE_TRIVIAL_CLEANUP_FUNC_FULL_RENAME(struct libmnt_iter*, sym_mnt_free_iter, mnt_free_iterp, NULL);
 
@@ -56,12 +58,14 @@ static inline int libmount_parse_mountinfo(
                 FILE *source,
                 struct libmnt_table **ret_table,
                 struct libmnt_iter **ret_iter) {
+
         return libmount_parse_full("/proc/self/mountinfo", source, MNT_ITER_FORWARD, ret_table, ret_iter);
 }
 
 static inline int libmount_parse_with_utab(
                 struct libmnt_table **ret_table,
                 struct libmnt_iter **ret_iter) {
+
         return libmount_parse_full(NULL, NULL, MNT_ITER_FORWARD, ret_table, ret_iter);
 }
 
@@ -70,15 +74,18 @@ int libmount_parse_fstab(struct libmnt_table **ret_table, struct libmnt_iter **r
 int libmount_is_leaf(
                 struct libmnt_table *table,
                 struct libmnt_fs *fs);
+
 #else
 
 struct libmnt_monitor;
 
-static inline void *sym_mnt_unref_monitor(struct libmnt_monitor *p) {
+static inline int dlopen_libmount(void) {
+        return -EOPNOTSUPP;
+}
+
+static inline void* sym_mnt_unref_monitor(struct libmnt_monitor *p) {
         assert(p == NULL);
         return NULL;
 }
 
 #endif
-
-int dlopen_libmount(void);

src/shared/meson.build

@@ -115,7 +115,6 @@ shared_sources = files(
         'libaudit-util.c',
         'libcrypt-util.c',
         'libfido2-util.c',
-        'libmount-util.c',
         'local-addresses.c',
         'locale-setup.c',
         'log-assert-critical.c',
@@ -239,10 +238,6 @@ shared_sources = files(
         'xml.c',
 )
 
-if conf.get('ENABLE_NSS') == 1
-        shared_sources += files('nss-util.c')
-endif
-
 if get_option('tests') != 'false'
         shared_sources += files('tests.c')
 endif
@@ -257,6 +252,10 @@ syscall_list_inc = custom_target(
 generated_sources += syscall_list_inc
 shared_sources += syscall_list_inc
 
+if conf.get('ENABLE_NSS') == 1
+        shared_sources += files('nss-util.c')
+endif
+
 if conf.get('ENABLE_UTMP') == 1
         shared_sources += files('utmp-wtmp.c')
 endif
@@ -269,6 +268,10 @@ if conf.get('HAVE_PAM') == 1
         shared_sources += files('pam-util.c')
 endif
 
+if conf.get('HAVE_LIBMOUNT') == 1
+        shared_sources += files('libmount-util.c')
+endif
+
 generate_ip_protocol_list = files('generate-ip-protocol-list.sh')
 ip_protocol_list_txt = custom_target(
         input : [generate_ip_protocol_list, ipproto_sources],