core: add new RestrictAddressFamilies= switch

This new unit settings allows restricting which address families are
available to processes. This is an effective way to minimize the attack
surface of services, by turning off entire network stacks for them.

This is based on seccomp, and does not work on x86-32, since seccomp
cannot filter socketcall() syscalls on that platform.

1 files changed, 50 insertions, 0 deletions

diff --git a/src/core/dbus-execute.c b/src/core/dbus-execute.c
index 935c62bdf..02e2a6d3d 100644
--- a/src/core/dbus-execute.c
+++ b/src/core/dbus-execute.c
@@ -34,6 +34,7 @@
 #include "dbus-execute.h"
 #include "capability.h"
 #include "env-util.h"
+#include "af-list.h"
 
 #ifdef HAVE_SECCOMP
 #include "seccomp-util.h"
@@ -518,6 +519,54 @@ static int property_get_personality(
         return sd_bus_message_append(reply, "s", personality_to_string(c->personality));
 }
 
+static int property_get_address_families(
+                sd_bus *bus,
+                const char *path,
+                const char *interface,
+                const char *property,
+                sd_bus_message *reply,
+                void *userdata,
+                sd_bus_error *error) {
+
+        ExecContext *c = userdata;
+        _cleanup_strv_free_ char **l = NULL;
+        Iterator i;
+        void *af;
+        int r;
+
+        assert(bus);
+        assert(reply);
+        assert(c);
+
+        r = sd_bus_message_open_container(reply, 'r', "bas");
+        if (r < 0)
+                return r;
+
+        r = sd_bus_message_append(reply, "b", c->address_families_whitelist);
+        if (r < 0)
+                return r;
+
+        SET_FOREACH(af, c->address_families, i) {
+                const char *name;
+
+                name = af_to_name(PTR_TO_INT(af));
+                if (!name)
+                        continue;
+
+                r = strv_extend(&l, name);
+                if (r < 0)
+                        return -ENOMEM;
+        }
+
+        strv_sort(l);
+
+        r = sd_bus_message_append_strv(reply, l);
+        if (r < 0)
+                return r;
+
+        return sd_bus_message_close_container(reply);
+}
+
 const sd_bus_vtable bus_exec_vtable[] = {
         SD_BUS_VTABLE_START(0),
         SD_BUS_PROPERTY("Environment", "as", NULL, offsetof(ExecContext, environment), SD_BUS_VTABLE_PROPERTY_CONST),
@@ -585,6 +634,7 @@ const sd_bus_vtable bus_exec_vtable[] = {
         SD_BUS_PROPERTY("SystemCallArchitectures", "as", property_get_syscall_archs, 0, SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("SystemCallErrorNumber", "i", property_get_syscall_errno, 0, SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("Personality", "s", property_get_personality, 0, SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("RestrictAddressFamilies", "(bas)", property_get_address_families, 0, SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_VTABLE_END
 };