core:sandbox: lets make /lib/modules/ inaccessible on ProtectKernelModules=

Lets go further and make /lib/modules/ inaccessible for services that do
not have business with modules, this is a minor improvment but it may
help on setups with custom modules and they are limited... in regard of
kernel auto-load feature.

This change introduce NameSpaceInfo struct which we may embed later
inside ExecContext but for now lets just reduce the argument number to
setup_namespace() and merge ProtectKernelModules feature.

3 files changed, 56 insertions, 23 deletions

diff --git a/src/core/execute.c b/src/core/execute.c
index 7a278b7d31..dc078d96f0 100644
--- a/src/core/execute.c
+++ b/src/core/execute.c
@@ -1766,6 +1766,7 @@ static bool exec_needs_mount_namespace(
             context->protect_system != PROTECT_SYSTEM_NO ||
             context->protect_home != PROTECT_HOME_NO ||
             context->protect_kernel_tunables ||
+            context->protect_kernel_modules ||
             context->protect_control_groups)
                 return true;
 
@@ -2493,6 +2494,12 @@ static int exec_child(
         if (needs_mount_namespace) {
                 _cleanup_free_ char **rw = NULL;
                 char *tmp = NULL, *var = NULL;
+                NameSpaceInfo ns_info = {
+                        .private_dev = context->private_devices,
+                        .protect_control_groups = context->protect_control_groups,
+                        .protect_kernel_tunables = context->protect_kernel_tunables,
+                        .protect_kernel_modules = context->protect_kernel_modules,
+                };
 
                 /* The runtime struct only contains the parent
                  * of the private /tmp, which is
@@ -2515,14 +2522,12 @@ static int exec_child(
 
                 r = setup_namespace(
                                 (params->flags & EXEC_APPLY_CHROOT) ? context->root_directory : NULL,
+                                &ns_info,
                                 rw,
                                 context->read_only_paths,
                                 context->inaccessible_paths,
                                 tmp,
                                 var,
-                                context->private_devices,
-                                context->protect_kernel_tunables,
-                                context->protect_control_groups,
                                 context->protect_home,
                                 context->protect_system,
                                 context->mount_flags);
diff --git a/src/core/namespace.c b/src/core/namespace.c
index 43a2f4ba6e..1195e9a854 100644
--- a/src/core/namespace.c
+++ b/src/core/namespace.c
@@ -97,6 +97,14 @@ static const TargetMount protect_kernel_tunables_table[] = {
         { "/sys/fs/cgroup",             READWRITE,      false }, /* READONLY is set by ProtectControlGroups= option */
 };
 
+/* ProtectKernelModules= option */
+static const TargetMount protect_kernel_modules_table[] = {
+#ifdef HAVE_SPLIT_USR
+        { "/lib/modules",               INACCESSIBLE,   true  },
+#endif
+        { "/usr/lib/modules",           INACCESSIBLE,   true  },
+};
+
 /*
  * ProtectHome=read-only table, protect $HOME and $XDG_RUNTIME_DIR and rest of
  * system should be protected by ProtectSystem=
@@ -207,6 +215,13 @@ static int append_protect_kernel_tunables(BindMount **p, const char *root_direct
                                     ELEMENTSOF(protect_kernel_tunables_table));
 }
 
+static int append_protect_kernel_modules(BindMount **p, const char *root_directory) {
+        assert(p);
+
+        return append_target_mounts(p, root_directory, protect_kernel_modules_table,
+                                    ELEMENTSOF(protect_kernel_modules_table));
+}
+
 static int append_protect_home(BindMount **p, const char *root_directory, ProtectHome protect_home) {
         int r = 0;
 
@@ -660,14 +675,12 @@ static int chase_all_symlinks(const char *root_directory, BindMount *m, unsigned
 }
 
 static unsigned namespace_calculate_mounts(
+                const NameSpaceInfo *ns_info,
                 char** read_write_paths,
                 char** read_only_paths,
                 char** inaccessible_paths,
                 const char* tmp_dir,
                 const char* var_tmp_dir,
-                bool private_dev,
-                bool protect_sysctl,
-                bool protect_cgroups,
                 ProtectHome protect_home,
                 ProtectSystem protect_system) {
 
@@ -690,22 +703,21 @@ static unsigned namespace_calculate_mounts(
                 strv_length(read_write_paths) +
                 strv_length(read_only_paths) +
                 strv_length(inaccessible_paths) +
-                private_dev +
-                (protect_sysctl ? ELEMENTSOF(protect_kernel_tunables_table) : 0) +
-                (protect_cgroups ? 1 : 0) +
+                ns_info->private_dev +
+                (ns_info->protect_kernel_tunables ? ELEMENTSOF(protect_kernel_tunables_table) : 0) +
+                (ns_info->protect_control_groups ? 1 : 0) +
+                (ns_info->protect_kernel_modules ? ELEMENTSOF(protect_kernel_modules_table) : 0) +
                 protect_home_cnt + protect_system_cnt;
 }
 
 int setup_namespace(
                 const char* root_directory,
+                const NameSpaceInfo *ns_info,
                 char** read_write_paths,
                 char** read_only_paths,
                 char** inaccessible_paths,
                 const char* tmp_dir,
                 const char* var_tmp_dir,
-                bool private_dev,
-                bool protect_sysctl,
-                bool protect_cgroups,
                 ProtectHome protect_home,
                 ProtectSystem protect_system,
                 unsigned long mount_flags) {
@@ -718,13 +730,12 @@ int setup_namespace(
         if (mount_flags == 0)
                 mount_flags = MS_SHARED;
 
-        n = namespace_calculate_mounts(read_write_paths,
+        n = namespace_calculate_mounts(ns_info,
+                                       read_write_paths,
                                        read_only_paths,
                                        inaccessible_paths,
                                        tmp_dir, var_tmp_dir,
-                                       private_dev, protect_sysctl,
-                                       protect_cgroups, protect_home,
-                                       protect_system);
+                                       protect_home, protect_system);
 
         /* Set mount slave mode */
         if (root_directory || n > 0)
@@ -756,16 +767,25 @@ int setup_namespace(
                         m++;
                 }
 
-                if (private_dev) {
+                if (ns_info->private_dev) {
                         m->path = prefix_roota(root_directory, "/dev");
                         m->mode = PRIVATE_DEV;
                         m++;
                 }
 
-                if (protect_sysctl)
-                        append_protect_kernel_tunables(&m, root_directory);
+                if (ns_info->protect_kernel_tunables) {
+                        r = append_protect_kernel_tunables(&m, root_directory);
+                        if (r < 0)
+                                return r;
+                }
+
+                if (ns_info->protect_kernel_modules) {
+                        r = append_protect_kernel_modules(&m, root_directory);
+                        if (r < 0)
+                                return r;
+                }
 
-                if (protect_cgroups) {
+                if (ns_info->protect_control_groups) {
                         m->path = prefix_roota(root_directory, "/sys/fs/cgroup");
                         m->mode = READONLY;
                         m++;
diff --git a/src/core/namespace.h b/src/core/namespace.h
index 6505bcc499..6310638e9a 100644
--- a/src/core/namespace.h
+++ b/src/core/namespace.h
@@ -4,6 +4,7 @@
   This file is part of systemd.
 
   Copyright 2010 Lennart Poettering
+  Copyright 2016 Djalal Harouni
 
   systemd is free software; you can redistribute it and/or modify it
   under the terms of the GNU Lesser General Public License as published by
@@ -19,6 +20,8 @@
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
 ***/
 
+typedef struct NameSpaceInfo NameSpaceInfo;
+
 #include <stdbool.h>
 
 #include "macro.h"
@@ -40,15 +43,20 @@ typedef enum ProtectSystem {
         _PROTECT_SYSTEM_INVALID = -1
 } ProtectSystem;
 
+struct NameSpaceInfo {
+        bool private_dev:1;
+        bool protect_control_groups:1;
+        bool protect_kernel_tunables:1;
+        bool protect_kernel_modules:1;
+};
+
 int setup_namespace(const char *chroot,
+                    const NameSpaceInfo *ns_info,
                     char **read_write_paths,
                     char **read_only_paths,
                     char **inaccessible_paths,
                     const char *tmp_dir,
                     const char *var_tmp_dir,
-                    bool private_dev,
-                    bool protect_sysctl,
-                    bool protect_cgroups,
                     ProtectHome protect_home,
                     ProtectSystem protect_system,
                     unsigned long mount_flags);