sysusers: emit audit events for user and group creation

Background: Fedora/RHEL are switching to sysusers.d metadata for creation of
users and groups for system users defined by packages
(https://fedoraproject.org/wiki/Changes/RPMSuportForSystemdSysusers).
Packages carry sysusers files. During package installation, rpm calls an
program to execute on this config. This program may either be
/usr/lib/rpm/sysusers.sh which calls useradd/groupadd, or
/usr/bin/systemd-sysusers. To match the functionality provided by
useradd/groupadd from the shadow-utils project, systemd-sysusers must emit
audit events so that it provides a drop-in replacement.

systemd-sysuers will emit audit events AUDIT_ADD_USER/AUDIT_ADD_GROUP when
adding users and groups. The operation "names" are copied from shadow-utils in
Fedora (which has a patch to change them from the upstream version), so the
format of the events that is generated on success should be identical.

The helper code is shared between sysusers and utmp-wtmp. I changed the
audit_fd variable to be unconditional. This way we can avoid ugly iffdefery
every time the variable would be used. The cost is that 4 bytes of unused
storage might be present. This is negligible, and the compiler might even be
able to optimize that away if it inlines things.

diff --git a/src/basic/audit-util.h b/src/basic/audit-util.h
index bc08388d419c28a639e67c7b41b573b5cd4f9c4d..1ea5610e6d39559ed3b4912a525fb8f8add64196 100644 (file)
--- a/src/basic/audit-util.h
+++ b/src/basic/audit-util.h
@@ -1,10 +1,16 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 #pragma once
 
+#if HAVE_AUDIT
+#  include <libaudit.h>
+#endif
+
 #include <stdbool.h>
 #include <stdint.h>
 #include <sys/types.h>
 
+#include "errno-util.h"
+#include "log.h"
 #include "pidref.h"
 
 #define AUDIT_SESSION_INVALID UINT32_MAX
@@ -17,3 +23,30 @@ bool use_audit(void);
 static inline bool audit_session_is_valid(uint32_t id) {
         return id > 0 && id != AUDIT_SESSION_INVALID;
 }
+
+/* The wrappers for audit_open() and audit_close() are inline functions so that we don't get a spurious
+ * linkage to libaudit in libbasic, but we also don't need to create a separate source file for two very
+ * short functions. */
+
+static inline int close_audit_fd(int fd) {
+#if HAVE_AUDIT
+        if (fd >= 0)
+                audit_close(fd);
+#else
+        assert(fd < 0);
+#endif
+        return -EBADF;
+}
+
+static inline int open_audit_fd_or_warn(void) {
+        int fd = -EBADF;
+
+#if HAVE_AUDIT
+        /* If the kernel lacks netlink or audit support, don't worry about it. */
+        fd = audit_open();
+        if (fd < 0)
+                return log_full_errno(ERRNO_IS_NOT_SUPPORTED(errno) ? LOG_DEBUG : LOG_WARNING,
+                                      errno, "Failed to connect to audit log, ignoring: %m");
+#endif
+        return fd;
+}

diff --git a/src/sysusers/meson.build b/src/sysusers/meson.build
index 123ff41d3f7383240e24a37301de1d8defdd43bc..c968f55110cd0ac062e4d6521aae39dabf295da3 100644 (file)
--- a/src/sysusers/meson.build
+++ b/src/sysusers/meson.build
@@ -9,6 +9,7 @@ executables += [
                 'name' : 'systemd-sysusers',
                 'public' : true,
                 'sources' : files('sysusers.c'),
+                'dependencies' : libaudit,
         },
         executable_template + {
                 'name' : 'systemd-sysusers.standalone',
@@ -20,6 +21,7 @@ executables += [
                         libshared_static,
                         libsystemd_static,
                 ],
+                'dependencies' : libaudit,
                 'build_by_default' : have_standalone_binaries,
                 'install' : have_standalone_binaries,
         },

diff --git a/src/sysusers/sysusers.c b/src/sysusers/sysusers.c
index 44253483dba028c894692a73ba76264a77bb0184..84eb9fc0c3b82125d36d1e2123df56076ef82dcb 100644 (file)
--- a/src/sysusers/sysusers.c
+++ b/src/sysusers/sysusers.c
@@ -3,6 +3,7 @@
 #include <getopt.h>
 
 #include "alloc-util.h"
+#include "audit-util.h"
 #include "build.h"
 #include "chase.h"
 #include "conf-files.h"
@@ -106,6 +107,8 @@ STATIC_DESTRUCTOR_REGISTER(arg_image, freep);
 STATIC_DESTRUCTOR_REGISTER(arg_image_policy, image_policy_freep);
 
 typedef struct Context {
+        int audit_fd;
+
         OrderedHashmap *users, *groups;
         OrderedHashmap *todo_uids, *todo_gids;
         OrderedHashmap *members;
@@ -126,6 +129,8 @@ typedef struct Context {
 static void context_done(Context *c) {
         assert(c);
 
+        c->audit_fd = close_audit_fd(c->audit_fd);
+
         ordered_hashmap_free(c->groups);
         ordered_hashmap_free(c->users);
         ordered_hashmap_free(c->members);
@@ -163,6 +168,48 @@ static void maybe_emit_login_defs_warning(Context *c) {
         c->login_defs_need_warning = false;
 }
 
+static void log_audit_accounts(Context *c, ItemType what) {
+#if HAVE_AUDIT
+        assert(c);
+        assert(IN_SET(what, ADD_USER, ADD_GROUP));
+
+        if (arg_dry_run || c->audit_fd < 0)
+                return;
+
+        Item *i;
+        int type = what == ADD_USER ? AUDIT_ADD_USER : AUDIT_ADD_GROUP;
+        const char *op = what == ADD_USER ? "adding-user" : "adding-group";
+
+        /* Notes:
+         *
+         * The op must not contain whitespace. The format with a dash matches what Fedora shadow-utils uses.
+         *
+         * We send id == -1, even though we know the number, in particular on success. This is because if we
+         * send the id, the generated audit message will not contain the name. The name seems more useful
+         * than the number, hence send just the name:
+         *
+         * type=ADD_USER msg=audit(01/10/2025 16:02:00.639:3854) :
+         *   pid=3846380 uid=root auid=zbyszek ses=2 msg='op=adding-user id=unknown(952) exe=systemd-sysusers ... res=success'
+         * vs.
+         * type=ADD_USER msg=audit(01/10/2025 16:03:15.457:3908) :
+         *   pid=3846607 uid=root auid=zbyszek ses=2 msg='op=adding-user acct=foo5 exe=systemd-sysusers ... res=success'
+         */
+
+        ORDERED_HASHMAP_FOREACH(i, what == ADD_USER ? c->todo_uids : c->todo_gids)
+                audit_log_acct_message(
+                                c->audit_fd,
+                                type,
+                                program_invocation_short_name,
+                                op,
+                                i->name,
+                                /* id= */ (unsigned) -1,
+                                /* host= */ NULL,
+                                /* addr= */ NULL,
+                                /* tty= */ NULL,
+                                /* success= */ 1);
+#endif
+}
+
 static int load_user_database(Context *c) {
         _cleanup_fclose_ FILE *f = NULL;
         const char *passwd_path;
@@ -971,6 +1018,8 @@ static int write_files(Context *c) {
                                                group_tmp, group_path);
                 group_tmp = mfree(group_tmp);
         }
+        /* OK, we have written the group entries successfully */
+        log_audit_accounts(c, ADD_GROUP);
         if (gshadow) {
                 r = rename_and_apply_smack_floor_label(gshadow_tmp, gshadow_path);
                 if (r < 0)
@@ -988,6 +1037,8 @@ static int write_files(Context *c) {
 
                 passwd_tmp = mfree(passwd_tmp);
         }
+        /* OK, we have written the user entries successfully */
+        log_audit_accounts(c, ADD_USER);
         if (shadow) {
                 r = rename_and_apply_smack_floor_label(shadow_tmp, shadow_path);
                 if (r < 0)
@@ -2232,6 +2283,7 @@ static int run(int argc, char *argv[]) {
 #endif
         _cleanup_close_ int lock = -EBADF;
         _cleanup_(context_done) Context c = {
+                .audit_fd = -EBADF,
                 .search_uid = UID_INVALID,
         };
 
@@ -2281,6 +2333,10 @@ static int run(int argc, char *argv[]) {
         assert(!arg_image);
 #endif
 
+        /* Prepare to emit audit events, but only if we're operating on the host system. */
+        if (!arg_root)
+                c.audit_fd = open_audit_fd_or_warn();
+
         /* If command line arguments are specified along with --replace, read all configuration files and
          * insert the positional arguments at the specified place. Otherwise, if command line arguments are
          * specified, execute just them, and finally, without --replace= or any positional arguments, just

diff --git a/src/update-utmp/update-utmp.c b/src/update-utmp/update-utmp.c
index a10e6d478a871d19da88b3599959f97ffe85b5a0..6df94140638a66394ebbbdbeca99ca9ff20a027c 100644 (file)
--- a/src/update-utmp/update-utmp.c
+++ b/src/update-utmp/update-utmp.c
@@ -5,12 +5,9 @@
 #include <sys/types.h>
 #include <unistd.h>
 
-#if HAVE_AUDIT
-#include <libaudit.h>
-#endif
-
 #include "sd-bus.h"
 
+#include "audit-util.h"
 #include "alloc-util.h"
 #include "bus-error.h"
 #include "bus-locator.h"
@@ -30,20 +27,14 @@
 
 typedef struct Context {
         sd_bus *bus;
-#if HAVE_AUDIT
         int audit_fd;
-#endif
 } Context;
 
 static void context_clear(Context *c) {
         assert(c);
 
         c->bus = sd_bus_flush_close_unref(c->bus);
-#if HAVE_AUDIT
-        if (c->audit_fd >= 0)
-                audit_close(c->audit_fd);
-        c->audit_fd = -EBADF;
-#endif
+        c->audit_fd = close_audit_fd(c->audit_fd);
 }
 
 static int get_startup_monotonic_time(Context *c, usec_t *ret) {
@@ -256,22 +247,14 @@ static int run(int argc, char *argv[]) {
         };
 
         _cleanup_(context_clear) Context c = {
-#if HAVE_AUDIT
                 .audit_fd = -EBADF,
-#endif
         };
 
         log_setup();
 
         umask(0022);
 
-#if HAVE_AUDIT
-        /* If the kernel lacks netlink or audit support, don't worry about it. */
-        c.audit_fd = audit_open();
-        if (c.audit_fd < 0)
-                log_full_errno(IN_SET(errno, EAFNOSUPPORT, EPROTONOSUPPORT) ? LOG_DEBUG : LOG_WARNING,
-                               errno, "Failed to connect to audit log, ignoring: %m");
-#endif
+        c.audit_fd = open_audit_fd_or_warn();
 
         return dispatch_verb(argc, argv, verbs, &c);
 }