core: set NoNewPrivileges for seccomp if we don't have CAP_SYS_ADMIN

The manpage of seccomp specify that using seccomp with
SECCOMP_SET_MODE_FILTER will return EACCES if the caller do not have
CAP_SYS_ADMIN set, or if the no_new_privileges bit is not set. Hence,
without NoNewPrivilege set, it is impossible to use a SystemCall*
directive with a User directive set in system mode.

Now, NoNewPrivileges is set if we are in user mode, or if we are in
system mode and we don't have CAP_SYS_ADMIN, and SystemCall*
directives are used.

2 files changed, 51 insertions, 22 deletions

diff --git a/src/core/execute.c b/src/core/execute.c
index 8ede9e9afb..0c311ec330 100644
--- a/src/core/execute.c
+++ b/src/core/execute.c
@@ -24,6 +24,7 @@
 #include <poll.h>
 #include <signal.h>
 #include <string.h>
+#include <sys/capability.h>
 #include <sys/personality.h>
 #include <sys/prctl.h>
 #include <sys/socket.h>
@@ -1824,6 +1825,11 @@ static int exec_child(
 
         if (params->apply_permissions) {
 
+                bool use_address_families = context->address_families_whitelist ||
+                        !set_isempty(context->address_families);
+                bool use_syscall_filter = context->syscall_whitelist ||
+                        !set_isempty(context->syscall_filter) ||
+                        !set_isempty(context->syscall_archs);
                 int secure_bits = context->secure_bits;
 
                 for (i = 0; i < _RLIMIT_MAX; i++) {
@@ -1890,15 +1896,15 @@ static int exec_child(
                                 return -errno;
                         }
 
-                if (context->no_new_privileges)
+                if (context->no_new_privileges ||
+                    (!have_effective_cap(CAP_SYS_ADMIN) && (use_address_families || use_syscall_filter)))
                         if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) < 0) {
                                 *exit_status = EXIT_NO_NEW_PRIVILEGES;
                                 return -errno;
                         }
 
 #ifdef HAVE_SECCOMP
-                if (context->address_families_whitelist ||
-                    !set_isempty(context->address_families)) {
+                if (use_address_families) {
                         r = apply_address_families(context);
                         if (r < 0) {
                                 *exit_status = EXIT_ADDRESS_FAMILIES;
@@ -1906,9 +1912,7 @@ static int exec_child(
                         }
                 }
 
-                if (context->syscall_whitelist ||
-                    !set_isempty(context->syscall_filter) ||
-                    !set_isempty(context->syscall_archs)) {
+                if (use_syscall_filter) {
                         r = apply_seccomp(context);
                         if (r < 0) {
                                 *exit_status = EXIT_SECCOMP;
diff --git a/src/test/test-execute.c b/src/test/test-execute.c
index 0d2e4bfc15..5645f5c086 100644
--- a/src/test/test-execute.c
+++ b/src/test/test-execute.c
@@ -130,6 +130,15 @@ static void test_exec_systemcallerrornumber(Manager *m) {
 #endif
 }
 
+static void test_exec_systemcall_system_mode_with_user(Manager *m) {
+#ifdef HAVE_SECCOMP
+        if (getpwnam("nobody"))
+                test(m, "exec-systemcallfilter-system-user.service", 0, CLD_EXITED);
+        else
+                log_error_errno(errno, "Skipping test_exec_systemcall_system_mode_with_user, could not find nobody user: %m");
+#endif
+}
+
 static void test_exec_user(Manager *m) {
         if (getpwnam("nobody"))
                 test(m, "exec-user.service", 0, CLD_EXITED);
@@ -267,8 +276,31 @@ static void test_exec_spec_interpolation(Manager *m) {
         test(m, "exec-spec-interpolation.service", 0, CLD_EXITED);
 }
 
+static int run_tests(ManagerRunningAs running_as, test_function_t *tests) {
+        test_function_t *test = NULL;
+        Manager *m = NULL;
+        int r;
+
+        assert_se(tests);
+
+        r = manager_new(running_as, true, &m);
+        if (MANAGER_SKIP_TEST(r)) {
+                printf("Skipping test: manager_new: %s\n", strerror(-r));
+                return EXIT_TEST_SKIP;
+        }
+        assert_se(r >= 0);
+        assert_se(manager_startup(m, NULL, NULL) >= 0);
+
+        for (test = tests; test && *test; test++)
+                (*test)(m);
+
+        manager_free(m);
+
+        return 0;
+}
+
 int main(int argc, char *argv[]) {
-        test_function_t tests[] = {
+        test_function_t user_tests[] = {
                 test_exec_workingdirectory,
                 test_exec_personality,
                 test_exec_ignoresigpipe,
@@ -291,8 +323,10 @@ int main(int argc, char *argv[]) {
                 test_exec_spec_interpolation,
                 NULL,
         };
-        test_function_t *test = NULL;
-        Manager *m = NULL;
+        test_function_t system_tests[] = {
+                test_exec_systemcall_system_mode_with_user,
+                NULL,
+        };
         int r;
 
         log_parse_environment();
@@ -317,18 +351,9 @@ int main(int argc, char *argv[]) {
         assert_se(unsetenv("VAR2") == 0);
         assert_se(unsetenv("VAR3") == 0);
 
-        r = manager_new(MANAGER_USER, true, &m);
-        if (MANAGER_SKIP_TEST(r)) {
-                printf("Skipping test: manager_new: %s\n", strerror(-r));
-                return EXIT_TEST_SKIP;
-        }
-        assert_se(r >= 0);
-        assert_se(manager_startup(m, NULL, NULL) >= 0);
-
-        for (test = tests; test && *test; test++)
-                (*test)(m);
+        r = run_tests(MANAGER_USER, user_tests);
+        if (r != 0)
+                return r;
 
-        manager_free(m);
-
-        return 0;
+        return run_tests(MANAGER_SYSTEM, system_tests);
 }