core: add new ReadOnlySystem= and ProtectedHome= settings for service units

ReadOnlySystem= uses fs namespaces to mount /usr and /boot read-only for
a service.

ProtectedHome= uses fs namespaces to mount /home and /run/user
inaccessible or read-only for a service.

This patch also enables these settings for all our long-running services.

Together they should be good building block for a minimal service
sandbox, removing the ability for services to modify the operating
system or access the user's private data.

8 files changed, 103 insertions, 3 deletions

diff --git a/src/core/dbus-execute.c b/src/core/dbus-execute.c
index 13b3d0dd14..2aa08c1435 100644
--- a/src/core/dbus-execute.c
+++ b/src/core/dbus-execute.c
@@ -35,6 +35,7 @@
 #include "capability.h"
 #include "env-util.h"
 #include "af-list.h"
+#include "namespace.h"
 
 #ifdef HAVE_SECCOMP
 #include "seccomp-util.h"
@@ -44,6 +45,8 @@ BUS_DEFINE_PROPERTY_GET_ENUM(bus_property_get_exec_output, exec_output, ExecOutp
 
 static BUS_DEFINE_PROPERTY_GET_ENUM(property_get_exec_input, exec_input, ExecInput);
 
+static BUS_DEFINE_PROPERTY_GET_ENUM(bus_property_get_protected_home, protected_home, ProtectedHome);
+
 static int property_get_environment_files(
                 sd_bus *bus,
                 const char *path,
@@ -626,6 +629,8 @@ const sd_bus_vtable bus_exec_vtable[] = {
         SD_BUS_PROPERTY("PrivateTmp", "b", bus_property_get_bool, offsetof(ExecContext, private_tmp), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("PrivateNetwork", "b", bus_property_get_bool, offsetof(ExecContext, private_network), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("PrivateDevices", "b", bus_property_get_bool, offsetof(ExecContext, private_devices), SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("ProtectedHome", "s", bus_property_get_protected_home, offsetof(ExecContext, protected_home), SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("ReadOnlySystem", "b", bus_property_get_bool, offsetof(ExecContext, read_only_system), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("SameProcessGroup", "b", bus_property_get_bool, offsetof(ExecContext, same_pgrp), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("UtmpIdentifier", "s", NULL, offsetof(ExecContext, utmp_id), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("SELinuxContext", "(bs)", property_get_selinux_context, 0, SD_BUS_VTABLE_PROPERTY_CONST),
diff --git a/src/core/execute.c b/src/core/execute.c
index af8e7c725b..ce8b9bcb8b 100644
--- a/src/core/execute.c
+++ b/src/core/execute.c
@@ -1569,7 +1569,9 @@ int exec_spawn(ExecCommand *command,
                     !strv_isempty(context->inaccessible_dirs) ||
                     context->mount_flags != 0 ||
                     (context->private_tmp && runtime && (runtime->tmp_dir || runtime->var_tmp_dir)) ||
-                    context->private_devices) {
+                    context->private_devices ||
+                    context->read_only_system ||
+                    context->protected_home != PROTECTED_HOME_NO) {
 
                         char *tmp = NULL, *var = NULL;
 
@@ -1593,8 +1595,9 @@ int exec_spawn(ExecCommand *command,
                                         tmp,
                                         var,
                                         context->private_devices,
+                                        context->protected_home,
+                                        context->read_only_system,
                                         context->mount_flags);
-
                         if (err < 0) {
                                 r = EXIT_NAMESPACE;
                                 goto fail_child;
@@ -2111,6 +2114,8 @@ void exec_context_dump(ExecContext *c, FILE* f, const char *prefix) {
                 "%sPrivateTmp: %s\n"
                 "%sPrivateNetwork: %s\n"
                 "%sPrivateDevices: %s\n"
+                "%sProtectedHome: %s\n"
+                "%sReadOnlySystem: %s\n"
                 "%sIgnoreSIGPIPE: %s\n",
                 prefix, c->umask,
                 prefix, c->working_directory ? c->working_directory : "/",
@@ -2119,6 +2124,8 @@ void exec_context_dump(ExecContext *c, FILE* f, const char *prefix) {
                 prefix, yes_no(c->private_tmp),
                 prefix, yes_no(c->private_network),
                 prefix, yes_no(c->private_devices),
+                prefix, protected_home_to_string(c->protected_home),
+                prefix, yes_no(c->read_only_system),
                 prefix, yes_no(c->ignore_sigpipe));
 
         STRV_FOREACH(e, c->environment)
diff --git a/src/core/execute.h b/src/core/execute.h
index c9e29ffc8a..3d6f77c8ef 100644
--- a/src/core/execute.h
+++ b/src/core/execute.h
@@ -39,6 +39,7 @@ typedef struct ExecRuntime ExecRuntime;
 #include "set.h"
 #include "fdset.h"
 #include "missing.h"
+#include "namespace.h"
 
 typedef enum ExecInput {
         EXEC_INPUT_NULL,
@@ -156,6 +157,8 @@ struct ExecContext {
         bool private_tmp;
         bool private_network;
         bool private_devices;
+        bool read_only_system;
+        ProtectedHome protected_home;
 
         bool no_new_privileges;
 
diff --git a/src/core/load-fragment-gperf.gperf.m4 b/src/core/load-fragment-gperf.gperf.m4
index 4c066a8b96..97382d4745 100644
--- a/src/core/load-fragment-gperf.gperf.m4
+++ b/src/core/load-fragment-gperf.gperf.m4
@@ -80,6 +80,8 @@ $1.InaccessibleDirectories,      config_parse_namespace_path_strv,   0,
 $1.PrivateTmp,                   config_parse_bool,                  0,                             offsetof($1, exec_context.private_tmp)
 $1.PrivateNetwork,               config_parse_bool,                  0,                             offsetof($1, exec_context.private_network)
 $1.PrivateDevices,               config_parse_bool,                  0,                             offsetof($1, exec_context.private_devices)
+$1.ReadOnlySystem,               config_parse_bool,                  0,                             offsetof($1, exec_context.read_only_system)
+$1.ProtectedHome,                config_parse_protected_home,        0,                             offsetof($1, exec_context)
 $1.MountFlags,                   config_parse_exec_mount_flags,      0,                             offsetof($1, exec_context)
 $1.Personality,                  config_parse_personality,           0,                             offsetof($1, exec_context.personality)
 $1.RuntimeDirectoryMode,         config_parse_mode,                  0,                             offsetof($1, exec_context.runtime_directory_mode)
diff --git a/src/core/load-fragment.c b/src/core/load-fragment.c
index 6403e41113..9df78082ae 100644
--- a/src/core/load-fragment.c
+++ b/src/core/load-fragment.c
@@ -3044,6 +3044,49 @@ int config_parse_no_new_privileges(
         return 0;
 }
 
+int config_parse_protected_home(
+                const char* unit,
+                const char *filename,
+                unsigned line,
+                const char *section,
+                unsigned section_line,
+                const char *lvalue,
+                int ltype,
+                const char *rvalue,
+                void *data,
+                void *userdata) {
+
+        ExecContext *c = data;
+        int k;
+
+        assert(filename);
+        assert(lvalue);
+        assert(rvalue);
+        assert(data);
+
+        /* Our enum shall be a superset of booleans, hence first try
+         * to parse as as boolean, and then as enum */
+
+        k = parse_boolean(rvalue);
+        if (k > 0)
+                c->protected_home = PROTECTED_HOME_YES;
+        else if (k == 0)
+                c->protected_home = PROTECTED_HOME_NO;
+        else {
+                ProtectedHome h;
+
+                h = protected_home_from_string(rvalue);
+                if (h < 0){
+                        log_syntax(unit, LOG_ERR, filename, line, -h, "Failed to parse protected home value, ignoring: %s", rvalue);
+                        return 0;
+                }
+
+                c->protected_home = h;
+        }
+
+        return 0;
+}
+
 #define FOLLOW_MAX 8
 
 static int open_follow(char **filename, FILE **_f, Set *names, char **_final) {
diff --git a/src/core/load-fragment.h b/src/core/load-fragment.h
index 9ef9caa999..279efa983c 100644
--- a/src/core/load-fragment.h
+++ b/src/core/load-fragment.h
@@ -97,6 +97,7 @@ int config_parse_set_status(const char *unit, const char *filename, unsigned lin
 int config_parse_namespace_path_strv(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 int config_parse_no_new_privileges(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 int config_parse_cpu_quota(const char *unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
+int config_parse_protected_home(const char* unit, const char *filename, unsigned line, const char *section, unsigned section_line, const char *lvalue, int ltype, const char *rvalue, void *data, void *userdata);
 
 /* gperf prototypes */
 const struct ConfigPerfItem* load_fragment_gperf_lookup(const char *key, unsigned length);
diff --git a/src/core/namespace.c b/src/core/namespace.c
index 9f15211cb6..de09e9f2c3 100644
--- a/src/core/namespace.c
+++ b/src/core/namespace.c
@@ -331,6 +331,8 @@ int setup_namespace(
                 char* tmp_dir,
                 char* var_tmp_dir,
                 bool private_dev,
+                ProtectedHome protected_home,
+                bool read_only_system,
                 unsigned mount_flags) {
 
         BindMount *m, *mounts = NULL;
@@ -347,7 +349,9 @@ int setup_namespace(
                 strv_length(read_write_dirs) +
                 strv_length(read_only_dirs) +
                 strv_length(inaccessible_dirs) +
-                private_dev;
+                private_dev +
+                (protected_home != PROTECTED_HOME_NO ? 2 : 0) +
+                (read_only_system ? 2 : 0);
 
         if (n > 0) {
                 m = mounts = (BindMount *) alloca(n * sizeof(BindMount));
@@ -381,6 +385,18 @@ int setup_namespace(
                         m++;
                 }
 
+                if (protected_home != PROTECTED_HOME_NO) {
+                        r = append_mounts(&m, STRV_MAKE("-/home", "-/run/user"), protected_home == PROTECTED_HOME_READ_ONLY ? READONLY : INACCESSIBLE);
+                        if (r < 0)
+                                return r;
+                }
+
+                if (read_only_system) {
+                        r = append_mounts(&m, STRV_MAKE("/usr", "-/boot"), READONLY);
+                        if (r < 0)
+                                return r;
+                }
+
                 assert(mounts + n == m);
 
                 qsort(mounts, n, sizeof(BindMount), mount_path_compare);
@@ -581,3 +597,11 @@ fail:
 
         return r;
 }
+
+static const char *const protected_home_table[_PROTECTED_HOME_MAX] = {
+        [PROTECTED_HOME_NO] = "no",
+        [PROTECTED_HOME_YES] = "yes",
+        [PROTECTED_HOME_READ_ONLY] = "read-only",
+};
+
+DEFINE_STRING_TABLE_LOOKUP(protected_home, ProtectedHome);
diff --git a/src/core/namespace.h b/src/core/namespace.h
index fb1fc6ec0d..b985bdf512 100644
--- a/src/core/namespace.h
+++ b/src/core/namespace.h
@@ -23,12 +23,24 @@
 
 #include <stdbool.h>
 
+#include "macro.h"
+
+typedef enum ProtectedHome {
+        PROTECTED_HOME_NO,
+        PROTECTED_HOME_YES,
+        PROTECTED_HOME_READ_ONLY,
+        _PROTECTED_HOME_MAX,
+        _PROTECTED_HOME_INVALID = -1
+} ProtectedHome;
+
 int setup_namespace(char **read_write_dirs,
                     char **read_only_dirs,
                     char **inaccessible_dirs,
                     char *tmp_dir,
                     char *var_tmp_dir,
                     bool private_dev,
+                    ProtectedHome protected_home,
+                    bool read_only_system,
                     unsigned mount_flags);
 
 int setup_tmp_dirs(const char *id,
@@ -36,3 +48,6 @@ int setup_tmp_dirs(const char *id,
                   char **var_tmp_dir);
 
 int setup_netns(int netns_storage_socket[2]);
+
+const char* protected_home_to_string(ProtectedHome p) _const_;
+ProtectedHome protected_home_from_string(const char *s) _pure_;