core:sandbox: Add ProtectKernelModules= option
This is useful to turn off explicit module load and unload operations on modular kernels. This option removes CAP_SYS_MODULE from the capability bounding set for the unit, and installs a system call filter to block module system calls. This option will not prevent the kernel from loading modules using the module auto-load feature which is a system wide operation.
This commit is contained in:
Djalal Harouni
parent
18e51a022c
commit
502d704e5e
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@ -1404,6 +1404,23 @@
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logging. This does not affect commands prefixed with <literal>+</literal>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>ProtectKernelModules=</varname></term>
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<listitem><para>Takes a boolean argument. If true, explicit module loading will
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be denied. This allows to turn off module load and unload operations on modular
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kernels. It is recomended to turn this on for most services that do not need special
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file systems or extra kernel modules to work. Default to off. Enabling this option
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removes <constant>CAP_SYS_MODULE</constant> from the capability bounding set for
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the unit, and installs a system call filter to block module system calls.
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Note that limited automatic module loading due to user configuration or kernel
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mapping tables might still happen as side effect of requested user operations,
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both privileged and unprivileged. To disable module auto-load feature please see
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<citerefentry><refentrytitle>sysctl.d</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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<constant>kernel.modules_disabled</constant> mechanism and
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<filename>/proc/sys/kernel/modules_disabled</filename> documentation.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>Personality=</varname></term>
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@ -708,6 +708,7 @@ const sd_bus_vtable bus_exec_vtable[] = {
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SD_BUS_PROPERTY("PrivateTmp", "b", bus_property_get_bool, offsetof(ExecContext, private_tmp), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_PROPERTY("PrivateDevices", "b", bus_property_get_bool, offsetof(ExecContext, private_devices), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_PROPERTY("ProtectKernelTunables", "b", bus_property_get_bool, offsetof(ExecContext, protect_kernel_tunables), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_PROPERTY("ProtectKernelModules", "b", bus_property_get_bool, offsetof(ExecContext, protect_kernel_modules), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_PROPERTY("ProtectControlGroups", "b", bus_property_get_bool, offsetof(ExecContext, protect_control_groups), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_PROPERTY("PrivateNetwork", "b", bus_property_get_bool, offsetof(ExecContext, private_network), SD_BUS_VTABLE_PROPERTY_CONST),
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SD_BUS_PROPERTY("PrivateUsers", "b", bus_property_get_bool, offsetof(ExecContext, private_users), SD_BUS_VTABLE_PROPERTY_CONST),
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@ -1075,7 +1076,7 @@ int bus_exec_context_set_transient_property(
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"PrivateTmp", "PrivateDevices", "PrivateNetwork", "PrivateUsers",
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"NoNewPrivileges", "SyslogLevelPrefix", "MemoryDenyWriteExecute",
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"RestrictRealtime", "DynamicUser", "RemoveIPC", "ProtectKernelTunables",
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"ProtectControlGroups")) {
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"ProtectKernelModules", "ProtectControlGroups")) {
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int b;
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r = sd_bus_message_read(message, "b", &b);
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@ -1111,6 +1112,8 @@ int bus_exec_context_set_transient_property(
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c->remove_ipc = b;
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else if (streq(name, "ProtectKernelTunables"))
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c->protect_kernel_tunables = b;
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else if (streq(name, "ProtectKernelModules"))
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c->protect_kernel_modules = b;
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else if (streq(name, "ProtectControlGroups"))
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c->protect_control_groups = b;
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@ -1436,6 +1436,50 @@ finish:
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return r;
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}
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static int apply_protect_kernel_modules(Unit *u, const ExecContext *c) {
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static const int module_syscalls[] = {
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SCMP_SYS(delete_module),
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SCMP_SYS(finit_module),
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SCMP_SYS(init_module),
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};
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scmp_filter_ctx *seccomp;
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unsigned i;
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int r;
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assert(c);
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/* Turn of module syscalls on ProtectKernelModules=yes */
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if (skip_seccomp_unavailable(u, "ProtectKernelModules="))
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return 0;
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seccomp = seccomp_init(SCMP_ACT_ALLOW);
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if (!seccomp)
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return -ENOMEM;
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r = seccomp_add_secondary_archs(seccomp);
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if (r < 0)
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goto finish;
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for (i = 0; i < ELEMENTSOF(module_syscalls); i++) {
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r = seccomp_rule_add(seccomp, SCMP_ACT_ERRNO(EPERM),
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module_syscalls[i], 0);
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if (r < 0)
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goto finish;
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}
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r = seccomp_attr_set(seccomp, SCMP_FLTATR_CTL_NNP, 0);
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if (r < 0)
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goto finish;
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r = seccomp_load(seccomp);
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finish:
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seccomp_release(seccomp);
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return r;
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}
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static int apply_private_devices(Unit *u, const ExecContext *c) {
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const SystemCallFilterSet *set;
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scmp_filter_ctx *seccomp;
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@ -2690,6 +2734,14 @@ static int exec_child(
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}
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}
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if (context->protect_kernel_modules) {
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r = apply_protect_kernel_modules(unit, context);
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if (r < 0) {
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*exit_status = EXIT_SECCOMP;
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return r;
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}
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}
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if (context->private_devices) {
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r = apply_private_devices(unit, context);
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if (r < 0) {
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@ -175,6 +175,7 @@ struct ExecContext {
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ProtectSystem protect_system;
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ProtectHome protect_home;
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bool protect_kernel_tunables;
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bool protect_kernel_modules;
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bool protect_control_groups;
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bool no_new_privileges;
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@ -90,6 +90,7 @@ $1.InaccessiblePaths, config_parse_namespace_path_strv, 0,
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$1.PrivateTmp, config_parse_bool, 0, offsetof($1, exec_context.private_tmp)
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$1.PrivateDevices, config_parse_bool, 0, offsetof($1, exec_context.private_devices)
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$1.ProtectKernelTunables, config_parse_bool, 0, offsetof($1, exec_context.protect_kernel_tunables)
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$1.ProtectKernelModules, config_parse_bool, 0, offsetof($1, exec_context.protect_kernel_modules)
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$1.ProtectControlGroups, config_parse_bool, 0, offsetof($1, exec_context.protect_control_groups)
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$1.PrivateNetwork, config_parse_bool, 0, offsetof($1, exec_context.private_network)
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$1.PrivateUsers, config_parse_bool, 0, offsetof($1, exec_context.private_users)
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@ -3401,6 +3401,9 @@ int unit_patch_contexts(Unit *u) {
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if (ec->private_devices)
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ec->capability_bounding_set &= ~(UINT64_C(1) << CAP_MKNOD);
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if (ec->protect_kernel_modules)
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ec->capability_bounding_set &= ~(UINT64_C(1) << CAP_SYS_MODULE);
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if (ec->dynamic_user) {
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if (!ec->user) {
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r = user_from_unit_name(u, &ec->user);
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@ -204,7 +204,8 @@ int bus_append_unit_property_assignment(sd_bus_message *m, const char *assignmen
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"IgnoreSIGPIPE", "TTYVHangup", "TTYReset", "RemainAfterExit",
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"PrivateTmp", "PrivateDevices", "PrivateNetwork", "PrivateUsers", "NoNewPrivileges",
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"SyslogLevelPrefix", "Delegate", "RemainAfterElapse", "MemoryDenyWriteExecute",
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"RestrictRealtime", "DynamicUser", "RemoveIPC", "ProtectKernelTunables", "ProtectControlGroups")) {
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"RestrictRealtime", "DynamicUser", "RemoveIPC", "ProtectKernelTunables",
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"ProtectKernelModules", "ProtectControlGroups")) {
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r = parse_boolean(eq);
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if (r < 0)
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