Merge pull request #12056 from poettering/seccomp-suid-sgid

Introduce RestrictSUIDSGID= for disabling SUID/SGID file creation

NEWS

@@ -201,6 +201,21 @@ CHANGES WITH 242 in spe:
           done anymore, and instead calling `systemctl preset-all` is
           recommended after the first installation of systemd.
 
+        * A new boolean sandboxing option RestrictSUIDSGID= has been added that
+          is built on seccomp. When turned on creation of SUID/SGID files is
+          prohibited.
+
+        * The NoNewPrivileges= and the new RestrictSUIDSGID= options are now
+          implied if DynamicUser= is turned on for a service. This hardens
+          these services, so that they neither can benefit from nor create
+          SUID/SGID executables. This is a minor compatibility breakage, given
+          that when DynamicUser= was first introduced SUID/SGID behaviour was
+          unaffected. However, the security benefit of these two options is
+          substantial, and the setting is still relatively new, hence we opted
+          to make it mandatory for services with dynamic users.
+
+        …
+
 CHANGES WITH 241:
 
         * The default locale can now be configured at compile time. Otherwise,

TODO

@@ -32,9 +32,6 @@ Features:
   - Make sure resume= and resume_offset= on the kernel cmdline always take
     precedence
 
-* maybe add a seccomp-based high-level filter that blocks creation of suid/sgid
-  files.
-
 * make MAINPID= message reception checks even stricter: if service uses User=,
   then check sending UID and ignore message if it doesn't match the user or
   root.

docs/TRANSIENT-SETTINGS.md

@@ -155,6 +155,7 @@ All execution-related settings are available for transient units.
 ✓ MemoryDenyWriteExecute=
 ✓ RestrictNamespaces=
 ✓ RestrictRealtime=
+✓ RestrictSUIDSGID=
 ✓ RestrictAddressFamilies=
 ✓ LockPersonality=
 ✓ LimitCPU=

man/systemd.exec.xml

@@ -252,7 +252,9 @@
         of the service, and hence the lifetime of the dynamic user/group. Since <filename>/tmp</filename> and
         <filename>/var/tmp</filename> are usually the only world-writable directories on a system this
         ensures that a unit making use of dynamic user/group allocation cannot leave files around after unit
-        termination. Moreover <varname>ProtectSystem=strict</varname> and
+        termination. Furthermore <varname>NoNewPrivileges=</varname> and <varname>RestrictSUIDSGID=</varname>
+        are implicitly enabled to ensure that processes invoked cannot take benefit or create SUID/SGID files
+        or directories. Moreover <varname>ProtectSystem=strict</varname> and
         <varname>ProtectHome=read-only</varname> are implied, thus prohibiting the service to write to
         arbitrary file system locations. In order to allow the service to write to certain directories, they
         have to be whitelisted using <varname>ReadWritePaths=</varname>, but care must be taken so that
@@ -379,19 +381,21 @@ CapabilityBoundingSet=~CAP_B CAP_C</programlisting>
       <varlistentry>
         <term><varname>NoNewPrivileges=</varname></term>
 
-        <listitem><para>Takes a boolean argument. If true, ensures that the service process and all its children can
-        never gain new privileges through <function>execve()</function> (e.g. via setuid or setgid bits, or filesystem
-        capabilities). This is the simplest and most effective way to ensure that a process and its children can never
-        elevate privileges again. Defaults to false, but certain settings override this and ignore the value of this
-        setting.  This is the case when <varname>SystemCallFilter=</varname>,
-        <varname>SystemCallArchitectures=</varname>, <varname>RestrictAddressFamilies=</varname>,
-        <varname>RestrictNamespaces=</varname>, <varname>PrivateDevices=</varname>,
-        <varname>ProtectKernelTunables=</varname>, <varname>ProtectKernelModules=</varname>,
-        <varname>MemoryDenyWriteExecute=</varname>, <varname>RestrictRealtime=</varname>, or
-        <varname>LockPersonality=</varname> are specified. Note that even if this setting is overridden by them,
-        <command>systemctl show</command> shows the original value of this setting. Also see
-        <ulink url="https://www.kernel.org/doc/html/latest/userspace-api/no_new_privs.html">No New Privileges
-        Flag</ulink>.  </para></listitem>
+        <listitem><para>Takes a boolean argument. If true, ensures that the service process and all its
+        children can never gain new privileges through <function>execve()</function> (e.g. via setuid or
+        setgid bits, or filesystem capabilities). This is the simplest and most effective way to ensure that
+        a process and its children can never elevate privileges again. Defaults to false, but certain
+        settings override this and ignore the value of this setting.  This is the case when
+        <varname>SystemCallFilter=</varname>, <varname>SystemCallArchitectures=</varname>,
+        <varname>RestrictAddressFamilies=</varname>, <varname>RestrictNamespaces=</varname>,
+        <varname>PrivateDevices=</varname>, <varname>ProtectKernelTunables=</varname>,
+        <varname>ProtectKernelModules=</varname>, <varname>MemoryDenyWriteExecute=</varname>,
+        <varname>RestrictRealtime=</varname>, <varname>RestrictSUIDSGID=</varname>,
+        <varname>DynamicUser=</varname> or <varname>LockPersonality=</varname> are specified. Note that even
+        if this setting is overridden by them, <command>systemctl show</command> shows the original value of
+        this setting. Also see <ulink
+        url="https://www.kernel.org/doc/html/latest/userspace-api/no_new_privs.html">No New Privileges
+        Flag</ulink>.</para></listitem>
       </varlistentry>
 
       <varlistentry>
@@ -1392,6 +1396,23 @@ RestrictNamespaces=~cgroup net</programlisting>
         that actually require them. Defaults to off.</para></listitem>
       </varlistentry>
 
+      <varlistentry>
+        <term><varname>RestrictSUIDSGID=</varname></term>
+
+        <listitem><para>Takes a boolean argument. If set, any attempts to set the set-user-ID (SUID) or
+        set-group-ID (SGID) bits on files or directories will be denied (for details on these bits see
+        <citerefentry
+        project='man-pages'><refentrytitle>inode</refentrytitle><manvolnum>7</manvolnum></citerefentry>). If
+        running in user mode, or in system mode, but without the <constant>CAP_SYS_ADMIN</constant>
+        capability (e.g. setting <varname>User=</varname>), <varname>NoNewPrivileges=yes</varname> is
+        implied. As the SUID/SGID bits are mechanisms to elevate privileges, and allows users to acquire the
+        identity of other users, it is recommended to restrict creation of SUID/SGID files to the few
+        programs that actually require them. Note that this restricts marking of any type of file system
+        object with these bits, including both regular files and directories (where the SGID is a different
+        meaning than for files, see documentation). This option is implied if <varname>DynamicUser=</varname>
+        is enabled. Defaults to off.</para></listitem>
+      </varlistentry>
+
       <varlistentry>
         <term><varname>RemoveIPC=</varname></term>
 

src/analyze/analyze-security.c

@@ -75,6 +75,7 @@ struct security_info {
 
         uint64_t restrict_namespaces;
         bool restrict_realtime;
+        bool restrict_suid_sgid;
 
         char *root_directory;
         char *root_image;
@@ -1148,6 +1149,16 @@ static const struct security_assessor security_assessor_table[] = {
                 .assess = assess_bool,
                 .offset = offsetof(struct security_info, restrict_realtime),
         },
+        {
+                .id = "RestrictSUIDSGID=",
+                .url = "https://www.freedesktop.org/software/systemd/man/systemd.exec.html#RestrictSUIDSGID=",
+                .description_good = "SUID/SGID file creation by service is restricted",
+                .description_bad = "Service may create SUID/SGID files",
+                .weight = 1000,
+                .range = 1,
+                .assess = assess_bool,
+                .offset = offsetof(struct security_info, restrict_suid_sgid),
+        },
         {
                 .id = "RestrictNamespaces=~CLONE_NEWUSER",
                 .url = "https://www.freedesktop.org/software/systemd/man/systemd.exec.html#RestrictNamespaces=",
@@ -1881,6 +1892,7 @@ static int acquire_security_info(sd_bus *bus, const char *name, struct security_
                 { "RestrictAddressFamilies", "(bas)",   property_read_restrict_address_families, 0                                                         },
                 { "RestrictNamespaces",      "t",       NULL,                                    offsetof(struct security_info, restrict_namespaces)       },
                 { "RestrictRealtime",        "b",       NULL,                                    offsetof(struct security_info, restrict_realtime)         },
+                { "RestrictSUIDSGID",        "b",       NULL,                                    offsetof(struct security_info, restrict_suid_sgid)        },
                 { "RootDirectory",           "s",       NULL,                                    offsetof(struct security_info, root_directory)            },
                 { "RootImage",               "s",       NULL,                                    offsetof(struct security_info, root_image)                },
                 { "SupplementaryGroups",     "as",      NULL,                                    offsetof(struct security_info, supplementary_groups)      },

src/core/dbus-execute.c

@@ -771,6 +771,7 @@ const sd_bus_vtable bus_exec_vtable[] = {
         SD_BUS_PROPERTY("ConfigurationDirectory", "as", NULL, offsetof(ExecContext, directories[EXEC_DIRECTORY_CONFIGURATION].paths), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("MemoryDenyWriteExecute", "b", bus_property_get_bool, offsetof(ExecContext, memory_deny_write_execute), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("RestrictRealtime", "b", bus_property_get_bool, offsetof(ExecContext, restrict_realtime), SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("RestrictSUIDSGID", "b", bus_property_get_bool, offsetof(ExecContext, restrict_suid_sgid), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("RestrictNamespaces", "t", bus_property_get_ulong, offsetof(ExecContext, restrict_namespaces), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("BindPaths", "a(ssbt)", property_get_bind_paths, 0, SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("BindReadOnlyPaths", "a(ssbt)", property_get_bind_paths, 0, SD_BUS_VTABLE_PROPERTY_CONST),
@@ -1128,6 +1129,9 @@ int bus_exec_context_set_transient_property(
         if (streq(name, "RestrictRealtime"))
                 return bus_set_transient_bool(u, name, &c->restrict_realtime, message, flags, error);
 
+        if (streq(name, "RestrictSUIDSGID"))
+                return bus_set_transient_bool(u, name, &c->restrict_suid_sgid, message, flags, error);
+
         if (streq(name, "DynamicUser"))
                 return bus_set_transient_bool(u, name, &c->dynamic_user, message, flags, error);
 

src/core/execute.c

@@ -1404,6 +1404,7 @@ static bool context_has_no_new_privileges(const ExecContext *c) {
         return context_has_address_families(c) ||
                 c->memory_deny_write_execute ||
                 c->restrict_realtime ||
+                c->restrict_suid_sgid ||
                 exec_context_restrict_namespaces_set(c) ||
                 c->protect_kernel_tunables ||
                 c->protect_kernel_modules ||
@@ -1509,6 +1510,19 @@ static int apply_restrict_realtime(const Unit* u, const ExecContext *c) {
         return seccomp_restrict_realtime();
 }
 
+static int apply_restrict_suid_sgid(const Unit* u, const ExecContext *c) {
+        assert(u);
+        assert(c);
+
+        if (!c->restrict_suid_sgid)
+                return 0;
+
+        if (skip_seccomp_unavailable(u, "RestrictSUIDSGID="))
+                return 0;
+
+        return seccomp_restrict_suid_sgid();
+}
+
 static int apply_protect_sysctl(const Unit *u, const ExecContext *c) {
         assert(u);
         assert(c);
@@ -3567,6 +3581,12 @@ static int exec_child(
                         return log_unit_error_errno(unit, r, "Failed to apply realtime restrictions: %m");
                 }
 
+                r = apply_restrict_suid_sgid(unit, context);
+                if (r < 0) {
+                        *exit_status = EXIT_SECCOMP;
+                        return log_unit_error_errno(unit, r, "Failed to apply SUID/SGID restrictions: %m");
+                }
+
                 r = apply_restrict_namespaces(unit, context);
                 if (r < 0) {
                         *exit_status = EXIT_SECCOMP;
@@ -4218,6 +4238,7 @@ void exec_context_dump(const ExecContext *c, FILE* f, const char *prefix) {
                 "%sIgnoreSIGPIPE: %s\n"
                 "%sMemoryDenyWriteExecute: %s\n"
                 "%sRestrictRealtime: %s\n"
+                "%sRestrictSUIDSGID: %s\n"
                 "%sKeyringMode: %s\n"
                 "%sProtectHostname: %s\n",
                 prefix, c->umask,
@@ -4237,6 +4258,7 @@ void exec_context_dump(const ExecContext *c, FILE* f, const char *prefix) {
                 prefix, yes_no(c->ignore_sigpipe),
                 prefix, yes_no(c->memory_deny_write_execute),
                 prefix, yes_no(c->restrict_realtime),
+                prefix, yes_no(c->restrict_suid_sgid),
                 prefix, exec_keyring_mode_to_string(c->keyring_mode),
                 prefix, yes_no(c->protect_hostname));
 

src/core/execute.h

@@ -261,6 +261,7 @@ struct ExecContext {
 
         bool memory_deny_write_execute;
         bool restrict_realtime;
+        bool restrict_suid_sgid;
 
         bool lock_personality;
         unsigned long personality;

src/core/load-fragment-gperf.gperf.m4

@@ -74,6 +74,7 @@ $1.SystemCallErrorNumber,        config_parse_syscall_errno,         0,
 $1.MemoryDenyWriteExecute,       config_parse_bool,                  0,                             offsetof($1, exec_context.memory_deny_write_execute)
 $1.RestrictNamespaces,           config_parse_restrict_namespaces,   0,                             offsetof($1, exec_context)
 $1.RestrictRealtime,             config_parse_bool,                  0,                             offsetof($1, exec_context.restrict_realtime)
+$1.RestrictSUIDSGID,             config_parse_bool,                  0,                             offsetof($1, exec_context.restrict_suid_sgid)
 $1.RestrictAddressFamilies,      config_parse_address_families,      0,                             offsetof($1, exec_context)
 $1.LockPersonality,              config_parse_bool,                  0,                             offsetof($1, exec_context.lock_personality)',
 `$1.SystemCallFilter,            config_parse_warn_compat,           DISABLED_CONFIGURATION,        0
@@ -82,6 +83,7 @@ $1.SystemCallErrorNumber,        config_parse_warn_compat,           DISABLED_CO
 $1.MemoryDenyWriteExecute,       config_parse_warn_compat,           DISABLED_CONFIGURATION,        0
 $1.RestrictNamespaces,           config_parse_warn_compat,           DISABLED_CONFIGURATION,        0
 $1.RestrictRealtime,             config_parse_warn_compat,           DISABLED_CONFIGURATION,        0
+$1.RestrictSUIDSGID,             config_parse_warn_compat,           DISABLED_CONFIGURATION         0
 $1.RestrictAddressFamilies,      config_parse_warn_compat,           DISABLED_CONFIGURATION,        0
 $1.LockPersonality,              config_parse_warn_compat,           DISABLED_CONFIGURATION,        0')
 $1.LimitCPU,                     config_parse_rlimit,                RLIMIT_CPU,                    offsetof($1, exec_context.rlimit)

src/core/unit.c

@@ -4088,14 +4088,20 @@ int unit_patch_contexts(Unit *u) {
                                         return -ENOMEM;
                         }
 
-                        /* If the dynamic user option is on, let's make sure that the unit can't leave its UID/GID
-                         * around in the file system or on IPC objects. Hence enforce a strict sandbox. */
+                        /* If the dynamic user option is on, let's make sure that the unit can't leave its
+                         * UID/GID around in the file system or on IPC objects. Hence enforce a strict
+                         * sandbox. */
 
                         ec->private_tmp = true;
                         ec->remove_ipc = true;
                         ec->protect_system = PROTECT_SYSTEM_STRICT;
                         if (ec->protect_home == PROTECT_HOME_NO)
                                 ec->protect_home = PROTECT_HOME_READ_ONLY;
+
+                        /* Make sure this service can neither benefit from SUID/SGID binaries nor create
+                         * them. */
+                        ec->no_new_privileges = true;
+                        ec->restrict_suid_sgid = true;
                 }
         }
 

src/shared/bus-unit-util.c

@@ -746,12 +746,12 @@ static int bus_append_execute_property(sd_bus_message *m, const char *field, con
                 return bus_append_string(m, field, eq);
 
         if (STR_IN_SET(field,
-                       "IgnoreSIGPIPE", "TTYVHangup", "TTYReset", "TTYVTDisallocate",
-                       "PrivateTmp", "PrivateDevices", "PrivateNetwork", "PrivateUsers",
-                       "PrivateMounts", "NoNewPrivileges", "SyslogLevelPrefix",
-                       "MemoryDenyWriteExecute", "RestrictRealtime", "DynamicUser", "RemoveIPC",
-                       "ProtectKernelTunables", "ProtectKernelModules", "ProtectControlGroups",
-                       "MountAPIVFS", "CPUSchedulingResetOnFork", "LockPersonality", "ProtectHostname"))
+                       "IgnoreSIGPIPE", "TTYVHangup", "TTYReset", "TTYVTDisallocate", "PrivateTmp",
+                       "PrivateDevices", "PrivateNetwork", "PrivateUsers", "PrivateMounts",
+                       "NoNewPrivileges", "SyslogLevelPrefix", "MemoryDenyWriteExecute", "RestrictRealtime",
+                       "DynamicUser", "RemoveIPC", "ProtectKernelTunables", "ProtectKernelModules",
+                       "ProtectControlGroups", "MountAPIVFS", "CPUSchedulingResetOnFork", "LockPersonality",
+                       "ProtectHostname", "RestrictSUIDSGID"))
 
                 return bus_append_parse_boolean(m, field, eq);
 

src/shared/seccomp-util.c

@@ -1,12 +1,14 @@
 /* SPDX-License-Identifier: LGPL-2.1+ */
 
 #include <errno.h>
+#include <fcntl.h>
 #include <linux/seccomp.h>
 #include <seccomp.h>
 #include <stddef.h>
 #include <sys/mman.h>
 #include <sys/prctl.h>
 #include <sys/shm.h>
+#include <sys/stat.h>
 
 #include "af-list.h"
 #include "alloc-util.h"
@@ -1776,16 +1778,20 @@ int seccomp_protect_hostname(void) {
                                 SCMP_ACT_ERRNO(EPERM),
                                 SCMP_SYS(sethostname),
                                 0);
-                if (r < 0)
+                if (r < 0) {
+                        log_debug_errno(r, "Failed to add sethostname() rule for architecture %s, skipping: %m", seccomp_arch_to_string(arch));
                         continue;
+                }
 
                 r = seccomp_rule_add_exact(
                                 seccomp,
                                 SCMP_ACT_ERRNO(EPERM),
                                 SCMP_SYS(setdomainname),
                                 0);
-                if (r < 0)
+                if (r < 0) {
+                        log_debug_errno(r, "Failed to add setdomainname() rule for architecture %s, skipping: %m", seccomp_arch_to_string(arch));
                         continue;
+                }
 
                 r = seccomp_load(seccomp);
                 if (IN_SET(r, -EPERM, -EACCES))
@@ -1796,3 +1802,133 @@ int seccomp_protect_hostname(void) {
 
         return 0;
 }
+
+int seccomp_restrict_suid_sgid(void) {
+        uint32_t arch;
+        int r;
+
+        SECCOMP_FOREACH_LOCAL_ARCH(arch) {
+                _cleanup_(seccomp_releasep) scmp_filter_ctx seccomp = NULL;
+
+                r = seccomp_init_for_arch(&seccomp, arch, SCMP_ACT_ALLOW);
+                if (r < 0)
+                        return r;
+
+                /* Checks the mode_t parameter of the following system calls:
+                 *
+                 *       → chmod() + fchmod() + fchmodat()
+                 *       → open() + creat() + openat()
+                 *       → mkdir() + mkdirat()
+                 *       → mknod() + mknodat()
+                 */
+
+                for (unsigned bit = 0; bit < 2; bit ++) {
+                        /* Block S_ISUID in the first iteration, S_ISGID in the second */
+                        mode_t m = bit == 0 ? S_ISUID : S_ISGID;
+
+                        r = seccomp_rule_add_exact(
+                                        seccomp,
+                                        SCMP_ACT_ERRNO(EPERM),
+                                        SCMP_SYS(chmod),
+                                        1,
+                                        SCMP_A1(SCMP_CMP_MASKED_EQ, m, m));
+                        if (r < 0)
+                                break;
+
+                        r = seccomp_rule_add_exact(
+                                        seccomp,
+                                        SCMP_ACT_ERRNO(EPERM),
+                                        SCMP_SYS(fchmod),
+                                        1,
+                                        SCMP_A1(SCMP_CMP_MASKED_EQ, m, m));
+                        if (r < 0)
+                                break;
+
+                        r = seccomp_rule_add_exact(
+                                        seccomp,
+                                        SCMP_ACT_ERRNO(EPERM),
+                                        SCMP_SYS(fchmodat),
+                                        1,
+                                        SCMP_A2(SCMP_CMP_MASKED_EQ, m, m));
+                        if (r < 0)
+                                break;
+
+                        r = seccomp_rule_add_exact(
+                                        seccomp,
+                                        SCMP_ACT_ERRNO(EPERM),
+                                        SCMP_SYS(mkdir),
+                                        1,
+                                        SCMP_A1(SCMP_CMP_MASKED_EQ, m, m));
+                        if (r < 0)
+                                break;
+
+                        r = seccomp_rule_add_exact(
+                                        seccomp,
+                                        SCMP_ACT_ERRNO(EPERM),
+                                        SCMP_SYS(mkdirat),
+                                        1,
+                                        SCMP_A2(SCMP_CMP_MASKED_EQ, m, m));
+                        if (r < 0)
+                                break;
+
+                        r = seccomp_rule_add_exact(
+                                        seccomp,
+                                        SCMP_ACT_ERRNO(EPERM),
+                                        SCMP_SYS(mknod),
+                                        1,
+                                        SCMP_A1(SCMP_CMP_MASKED_EQ, m, m));
+                        if (r < 0)
+                                break;
+
+                        r = seccomp_rule_add_exact(
+                                        seccomp,
+                                        SCMP_ACT_ERRNO(EPERM),
+                                        SCMP_SYS(mknodat),
+                                        1,
+                                        SCMP_A2(SCMP_CMP_MASKED_EQ, m, m));
+                        if (r < 0)
+                                break;
+
+                        r = seccomp_rule_add_exact(
+                                        seccomp,
+                                        SCMP_ACT_ERRNO(EPERM),
+                                        SCMP_SYS(open),
+                                        2,
+                                        SCMP_A1(SCMP_CMP_MASKED_EQ, O_CREAT, O_CREAT),
+                                        SCMP_A2(SCMP_CMP_MASKED_EQ, m, m));
+                        if (r < 0)
+                                break;
+
+                        r = seccomp_rule_add_exact(
+                                        seccomp,
+                                        SCMP_ACT_ERRNO(EPERM),
+                                        SCMP_SYS(openat),
+                                        2,
+                                        SCMP_A2(SCMP_CMP_MASKED_EQ, O_CREAT, O_CREAT),
+                                        SCMP_A3(SCMP_CMP_MASKED_EQ, m, m));
+                        if (r < 0)
+                                break;
+
+                        r = seccomp_rule_add_exact(
+                                        seccomp,
+                                        SCMP_ACT_ERRNO(EPERM),
+                                        SCMP_SYS(creat),
+                                        1,
+                                        SCMP_A1(SCMP_CMP_MASKED_EQ, m, m));
+                        if (r < 0)
+                                break;
+                }
+                if (r < 0) {
+                        log_debug_errno(r, "Failed to add suid/sgid rule for architecture %s, skipping: %m", seccomp_arch_to_string(arch));
+                        continue;
+                }
+
+                r = seccomp_load(seccomp);
+                if (IN_SET(r, -EPERM, -EACCES))
+                        return r;
+                if (r < 0)
+                        log_debug_errno(r, "Failed to apply suid/sgid restrictions for architecture %s, skipping: %m", seccomp_arch_to_string(arch));
+        }
+
+        return 0;
+}

src/shared/seccomp-util.h

@@ -86,6 +86,7 @@ int seccomp_restrict_realtime(void);
 int seccomp_memory_deny_write_execute(void);
 int seccomp_lock_personality(unsigned long personality);
 int seccomp_protect_hostname(void);
+int seccomp_restrict_suid_sgid(void);
 
 extern const uint32_t seccomp_local_archs[];
 

src/test/test-seccomp.c

@@ -19,10 +19,12 @@
 #include "nulstr-util.h"
 #include "process-util.h"
 #include "raw-clone.h"
+#include "rm-rf.h"
 #include "seccomp-util.h"
 #include "set.h"
 #include "string-util.h"
 #include "tests.h"
+#include "tmpfile-util.h"
 #include "virt.h"
 
 #if SCMP_SYS(socket) < 0 || defined(__i386__) || defined(__s390x__) || defined(__s390__)
@@ -759,6 +761,211 @@ static void test_lock_personality(void) {
         assert_se(wait_for_terminate_and_check("lockpersonalityseccomp", pid, WAIT_LOG) == EXIT_SUCCESS);
 }
 
+static int real_open(const char *path, int flags, mode_t mode) {
+        /* glibc internally calls openat() when open() is requested. Let's hence define our own wrapper for
+         * testing purposes that calls the real syscall. */
+
+        return (int) syscall(SYS_open, path, flags, mode);
+}
+
+static void test_restrict_suid_sgid(void) {
+        pid_t pid;
+
+        log_info("/* %s */", __func__);
+
+        if (!is_seccomp_available()) {
+                log_notice("Seccomp not available, skipping %s", __func__);
+                return;
+        }
+        if (geteuid() != 0) {
+                log_notice("Not root, skipping %s", __func__);
+                return;
+        }
+
+        pid = fork();
+        assert_se(pid >= 0);
+
+        if (pid == 0) {
+                char path[] = "/tmp/suidsgidXXXXXX", dir[] = "/tmp/suidsgiddirXXXXXX";
+                int fd = -1, k = -1;
+                const char *z;
+
+                fd = mkostemp_safe(path);
+                assert_se(fd >= 0);
+
+                assert_se(mkdtemp(dir));
+                z = strjoina(dir, "/test");
+
+                assert_se(chmod(path, 0755 | S_ISUID) >= 0);
+                assert_se(chmod(path, 0755 | S_ISGID) >= 0);
+                assert_se(chmod(path, 0755 | S_ISGID | S_ISUID) >= 0);
+                assert_se(chmod(path, 0755) >= 0);
+
+                assert_se(fchmod(fd, 0755 | S_ISUID) >= 0);
+                assert_se(fchmod(fd, 0755 | S_ISGID) >= 0);
+                assert_se(fchmod(fd, 0755 | S_ISGID | S_ISUID) >= 0);
+                assert_se(fchmod(fd, 0755) >= 0);
+
+                assert_se(fchmodat(AT_FDCWD, path, 0755 | S_ISUID, 0) >= 0);
+                assert_se(fchmodat(AT_FDCWD, path, 0755 | S_ISGID, 0) >= 0);
+                assert_se(fchmodat(AT_FDCWD, path, 0755 | S_ISGID | S_ISUID, 0) >= 0);
+                assert_se(fchmodat(AT_FDCWD, path, 0755, 0) >= 0);
+
+                k = real_open(z, O_CREAT|O_RDWR|O_CLOEXEC|O_EXCL, 0644 | S_ISUID);
+                k = safe_close(k);
+                assert_se(unlink(z) >= 0);
+
+                k = real_open(z, O_CREAT|O_RDWR|O_CLOEXEC|O_EXCL, 0644 | S_ISGID);
+                k = safe_close(k);
+                assert_se(unlink(z) >= 0);
+
+                k = real_open(z, O_CREAT|O_RDWR|O_CLOEXEC|O_EXCL, 0644 | S_ISUID | S_ISGID);
+                k = safe_close(k);
+                assert_se(unlink(z) >= 0);
+
+                k = real_open(z, O_CREAT|O_RDWR|O_CLOEXEC|O_EXCL, 0644);
+                k = safe_close(k);
+                assert_se(unlink(z) >= 0);
+
+                k = creat(z, 0644 | S_ISUID);
+                k = safe_close(k);
+                assert_se(unlink(z) >= 0);
+
+                k = creat(z, 0644 | S_ISGID);
+                k = safe_close(k);
+                assert_se(unlink(z) >= 0);
+
+                k = creat(z, 0644 | S_ISUID | S_ISGID);
+                k = safe_close(k);
+                assert_se(unlink(z) >= 0);
+
+                k = creat(z, 0644);
+                k = safe_close(k);
+                assert_se(unlink(z) >= 0);
+
+                k = openat(AT_FDCWD, z, O_CREAT|O_RDWR|O_CLOEXEC|O_EXCL, 0644 | S_ISUID);
+                k = safe_close(k);
+                assert_se(unlink(z) >= 0);
+
+                k = openat(AT_FDCWD, z, O_CREAT|O_RDWR|O_CLOEXEC|O_EXCL, 0644 | S_ISGID);
+                k = safe_close(k);
+                assert_se(unlink(z) >= 0);
+
+                k = openat(AT_FDCWD, z, O_CREAT|O_RDWR|O_CLOEXEC|O_EXCL, 0644 | S_ISUID | S_ISGID);
+                k = safe_close(k);
+                assert_se(unlink(z) >= 0);
+
+                k = openat(AT_FDCWD, z, O_CREAT|O_RDWR|O_CLOEXEC|O_EXCL, 0644);
+                k = safe_close(k);
+                assert_se(unlink(z) >= 0);
+
+                assert_se(mkdir(z, 0755 | S_ISUID) >= 0);
+                assert_se(rmdir(z) >= 0);
+                assert_se(mkdir(z, 0755 | S_ISGID) >= 0);
+                assert_se(rmdir(z) >= 0);
+                assert_se(mkdir(z, 0755 | S_ISUID | S_ISGID) >= 0);
+                assert_se(rmdir(z) >= 0);
+                assert_se(mkdir(z, 0755) >= 0);
+                assert_se(rmdir(z) >= 0);
+
+                assert_se(mkdirat(AT_FDCWD, z, 0755 | S_ISUID) >= 0);
+                assert_se(rmdir(z) >= 0);
+                assert_se(mkdirat(AT_FDCWD, z, 0755 | S_ISGID) >= 0);
+                assert_se(rmdir(z) >= 0);
+                assert_se(mkdirat(AT_FDCWD, z, 0755 | S_ISUID | S_ISGID) >= 0);
+                assert_se(rmdir(z) >= 0);
+                assert_se(mkdirat(AT_FDCWD, z, 0755) >= 0);
+                assert_se(rmdir(z) >= 0);
+
+                assert_se(mknod(z, S_IFREG | 0755 | S_ISUID, 0) >= 0);
+                assert_se(unlink(z) >= 0);
+                assert_se(mknod(z, S_IFREG | 0755 | S_ISGID, 0) >= 0);
+                assert_se(unlink(z) >= 0);
+                assert_se(mknod(z, S_IFREG | 0755 | S_ISUID | S_ISGID, 0) >= 0);
+                assert_se(unlink(z) >= 0);
+                assert_se(mknod(z, S_IFREG | 0755, 0) >= 0);
+                assert_se(unlink(z) >= 0);
+
+                assert_se(mknodat(AT_FDCWD, z, S_IFREG | 0755 | S_ISUID, 0) >= 0);
+                assert_se(unlink(z) >= 0);
+                assert_se(mknodat(AT_FDCWD, z, S_IFREG | 0755 | S_ISGID, 0) >= 0);
+                assert_se(unlink(z) >= 0);
+                assert_se(mknodat(AT_FDCWD, z, S_IFREG | 0755 | S_ISUID | S_ISGID, 0) >= 0);
+                assert_se(unlink(z) >= 0);
+                assert_se(mknodat(AT_FDCWD, z, S_IFREG | 0755, 0) >= 0);
+                assert_se(unlink(z) >= 0);
+
+                assert_se(seccomp_restrict_suid_sgid() >= 0);
+
+                assert_se(chmod(path, 0775 | S_ISUID) < 0 && errno == EPERM);
+                assert_se(chmod(path, 0775 | S_ISGID) < 0  && errno == EPERM);
+                assert_se(chmod(path, 0775 | S_ISGID | S_ISUID) < 0  && errno == EPERM);
+                assert_se(chmod(path, 0775) >= 0);
+
+                assert_se(fchmod(fd, 0775 | S_ISUID) < 0 && errno == EPERM);
+                assert_se(fchmod(fd, 0775 | S_ISGID) < 0  && errno == EPERM);
+                assert_se(fchmod(fd, 0775 | S_ISGID | S_ISUID) < 0  && errno == EPERM);
+                assert_se(fchmod(fd, 0775) >= 0);
+
+                assert_se(fchmodat(AT_FDCWD, path, 0755 | S_ISUID, 0) < 0 && errno == EPERM);
+                assert_se(fchmodat(AT_FDCWD, path, 0755 | S_ISGID, 0) < 0 && errno == EPERM);
+                assert_se(fchmodat(AT_FDCWD, path, 0755 | S_ISGID | S_ISUID, 0) < 0 && errno == EPERM);
+                assert_se(fchmodat(AT_FDCWD, path, 0755, 0) >= 0);
+
+                assert_se(real_open(z, O_CREAT|O_RDWR|O_CLOEXEC|O_EXCL, 0644 | S_ISUID) < 0 && errno == EPERM);
+                assert_se(real_open(z, O_CREAT|O_RDWR|O_CLOEXEC|O_EXCL, 0644 | S_ISGID) < 0 && errno == EPERM);
+                assert_se(real_open(z, O_CREAT|O_RDWR|O_CLOEXEC|O_EXCL, 0644 | S_ISUID | S_ISGID) < 0 && errno == EPERM);
+                k = real_open(z, O_CREAT|O_RDWR|O_CLOEXEC|O_EXCL, 0644);
+                k = safe_close(k);
+                assert_se(unlink(z) >= 0);
+
+                assert_se(creat(z, 0644 | S_ISUID) < 0 && errno == EPERM);
+                assert_se(creat(z, 0644 | S_ISGID) < 0 && errno == EPERM);
+                assert_se(creat(z, 0644 | S_ISUID | S_ISGID) < 0 && errno == EPERM);
+                k = creat(z, 0644);
+                k = safe_close(k);
+                assert_se(unlink(z) >= 0);
+
+                assert_se(openat(AT_FDCWD, z, O_CREAT|O_RDWR|O_CLOEXEC|O_EXCL, 0644 | S_ISUID) < 0 && errno == EPERM);
+                assert_se(openat(AT_FDCWD, z, O_CREAT|O_RDWR|O_CLOEXEC|O_EXCL, 0644 | S_ISGID) < 0 && errno == EPERM);
+                assert_se(openat(AT_FDCWD, z, O_CREAT|O_RDWR|O_CLOEXEC|O_EXCL, 0644 | S_ISUID | S_ISGID) < 0 && errno == EPERM);
+                k = openat(AT_FDCWD, z, O_CREAT|O_RDWR|O_CLOEXEC|O_EXCL, 0644);
+                k = safe_close(k);
+                assert_se(unlink(z) >= 0);
+
+                assert_se(mkdir(z, 0755 | S_ISUID) < 0 && errno == EPERM);
+                assert_se(mkdir(z, 0755 | S_ISGID) < 0 && errno == EPERM);
+                assert_se(mkdir(z, 0755 | S_ISUID | S_ISGID) < 0 && errno == EPERM);
+                assert_se(mkdir(z, 0755) >= 0);
+                assert_se(rmdir(z) >= 0);
+
+                assert_se(mkdirat(AT_FDCWD, z, 0755 | S_ISUID) < 0 && errno == EPERM);
+                assert_se(mkdirat(AT_FDCWD, z, 0755 | S_ISGID) < 0 && errno == EPERM);
+                assert_se(mkdirat(AT_FDCWD, z, 0755 | S_ISUID | S_ISGID) < 0 && errno == EPERM);
+                assert_se(mkdirat(AT_FDCWD, z, 0755) >= 0);
+                assert_se(rmdir(z) >= 0);
+
+                assert_se(mknod(z, S_IFREG | 0755 | S_ISUID, 0) < 0 && errno == EPERM);
+                assert_se(mknod(z, S_IFREG | 0755 | S_ISGID, 0) < 0 && errno == EPERM);
+                assert_se(mknod(z, S_IFREG | 0755 | S_ISUID | S_ISGID, 0) < 0 && errno == EPERM);
+                assert_se(mknod(z, S_IFREG | 0755, 0) >= 0);
+                assert_se(unlink(z) >= 0);
+
+                assert_se(mknodat(AT_FDCWD, z, S_IFREG | 0755 | S_ISUID, 0) < 0 && errno == EPERM);
+                assert_se(mknodat(AT_FDCWD, z, S_IFREG | 0755 | S_ISGID, 0) < 0 && errno == EPERM);
+                assert_se(mknodat(AT_FDCWD, z, S_IFREG | 0755 | S_ISUID | S_ISGID, 0) < 0 && errno == EPERM);
+                assert_se(mknodat(AT_FDCWD, z, S_IFREG | 0755, 0) >= 0);
+                assert_se(unlink(z) >= 0);
+
+                assert_se(unlink(path) >= 0);
+                assert_se(rm_rf(dir, REMOVE_ROOT|REMOVE_PHYSICAL) >= 0);
+
+                _exit(EXIT_SUCCESS);
+        }
+
+        assert_se(wait_for_terminate_and_check("suidsgidseccomp", pid, WAIT_LOG) == EXIT_SUCCESS);
+}
+
 int main(int argc, char *argv[]) {
         test_setup_logging(LOG_DEBUG);
 
@@ -776,6 +983,7 @@ int main(int argc, char *argv[]) {
         test_restrict_archs();
         test_load_syscall_filter_set_raw();
         test_lock_personality();
+        test_restrict_suid_sgid();
 
         return 0;
 }

test/fuzz/fuzz-unit-file/directives.service

@@ -851,6 +851,7 @@ ReserveVT=
 RestrictAddressFamilies=
 RestrictNamespaces=
 RestrictRealtime=
+RestrictSUIDSGID=
 RuntimeDirectory=
 RuntimeDirectoryMode=
 RuntimeDirectoryPreserve=

units/systemd-coredump@.service.in

@@ -36,6 +36,7 @@ ProtectSystem=strict
 RestrictAddressFamilies=AF_UNIX
 RestrictNamespaces=yes
 RestrictRealtime=yes
+RestrictSUIDSGID=yes
 RuntimeMaxSec=5min
 StateDirectory=systemd/coredump
 SystemCallArchitectures=native

units/systemd-hostnamed.service.in

@@ -32,6 +32,7 @@ ReadWritePaths=/etc
 RestrictAddressFamilies=AF_UNIX
 RestrictNamespaces=yes
 RestrictRealtime=yes
+RestrictSUIDSGID=yes
 SystemCallArchitectures=native
 SystemCallErrorNumber=EPERM
 SystemCallFilter=@system-service sethostname

units/systemd-journal-gatewayd.service.in

@@ -17,7 +17,6 @@ DynamicUser=yes
 ExecStart=@rootlibexecdir@/systemd-journal-gatewayd
 LockPersonality=yes
 MemoryDenyWriteExecute=yes
-NoNewPrivileges=yes
 PrivateDevices=yes
 PrivateNetwork=yes
 ProtectControlGroups=yes

units/systemd-journal-remote.service.in

@@ -30,6 +30,7 @@ ProtectSystem=strict
 RestrictAddressFamilies=AF_UNIX AF_INET AF_INET6
 RestrictNamespaces=yes
 RestrictRealtime=yes
+RestrictSUIDSGID=yes
 SystemCallArchitectures=native
 User=systemd-journal-remote
 WatchdogSec=3min

units/systemd-journal-upload.service.in

@@ -18,7 +18,6 @@ DynamicUser=yes
 ExecStart=@rootlibexecdir@/systemd-journal-upload --save-state
 LockPersonality=yes
 MemoryDenyWriteExecute=yes
-NoNewPrivileges=yes
 PrivateDevices=yes
 ProtectControlGroups=yes
 ProtectHome=yes

units/systemd-journald.service.in

@@ -28,6 +28,7 @@ RestartSec=0
 RestrictAddressFamilies=AF_UNIX AF_NETLINK
 RestrictNamespaces=yes
 RestrictRealtime=yes
+RestrictSUIDSGID=yes
 Sockets=systemd-journald.socket systemd-journald-dev-log.socket systemd-journald-audit.socket
 StandardOutput=null
 SystemCallArchitectures=native

units/systemd-localed.service.in

@@ -33,6 +33,7 @@ ReadWritePaths=/etc
 RestrictAddressFamilies=AF_UNIX
 RestrictNamespaces=yes
 RestrictRealtime=yes
+RestrictSUIDSGID=yes
 SystemCallArchitectures=native
 SystemCallErrorNumber=EPERM
 SystemCallFilter=@system-service

units/systemd-logind.service.in

@@ -40,6 +40,7 @@ RestartSec=0
 RestrictAddressFamilies=AF_UNIX AF_NETLINK
 RestrictNamespaces=yes
 RestrictRealtime=yes
+RestrictSUIDSGID=yes
 RuntimeDirectory=systemd/sessions systemd/seats systemd/users systemd/inhibit systemd/shutdown
 RuntimeDirectoryPreserve=yes
 SystemCallArchitectures=native

units/systemd-networkd.service.in

@@ -34,6 +34,7 @@ RestartSec=0
 RestrictAddressFamilies=AF_UNIX AF_NETLINK AF_INET AF_INET6 AF_PACKET
 RestrictNamespaces=yes
 RestrictRealtime=yes
+RestrictSUIDSGID=yes
 RuntimeDirectory=systemd/netif
 RuntimeDirectoryPreserve=yes
 SystemCallArchitectures=native

units/systemd-resolved.service.in

@@ -38,6 +38,7 @@ RestartSec=0
 RestrictAddressFamilies=AF_UNIX AF_NETLINK AF_INET AF_INET6
 RestrictNamespaces=yes
 RestrictRealtime=yes
+RestrictSUIDSGID=yes
 RuntimeDirectory=systemd/resolve
 RuntimeDirectoryPreserve=yes
 SystemCallArchitectures=native

units/systemd-timedated.service.in

@@ -31,6 +31,7 @@ ReadWritePaths=/etc
 RestrictAddressFamilies=AF_UNIX
 RestrictNamespaces=yes
 RestrictRealtime=yes
+RestrictSUIDSGID=yes
 SystemCallArchitectures=native
 SystemCallErrorNumber=EPERM
 SystemCallFilter=@system-service @clock

units/systemd-timesyncd.service.in

@@ -38,6 +38,7 @@ RestartSec=0
 RestrictAddressFamilies=AF_UNIX AF_INET AF_INET6
 RestrictNamespaces=yes
 RestrictRealtime=yes
+RestrictSUIDSGID=yes
 RuntimeDirectory=systemd/timesync
 StateDirectory=systemd/timesync
 SystemCallArchitectures=native

units/systemd-udevd.service.in

@@ -28,8 +28,9 @@ TasksMax=infinity
 PrivateMounts=yes
 ProtectHostname=yes
 MemoryDenyWriteExecute=yes
-RestrictRealtime=yes
 RestrictAddressFamilies=AF_UNIX AF_NETLINK AF_INET AF_INET6
+RestrictRealtime=yes
+RestrictSUIDSGID=yes
 SystemCallFilter=@system-service @module @raw-io
 SystemCallErrorNumber=EPERM
 SystemCallArchitectures=native