selftests/seccomp: Test PTRACE_O_SUSPEND_SECCOMP without CAP_SYS_ADMIN

Add a test to check that PTRACE_O_SUSPEND_SECCOMP can't be set without
CAP_SYS_ADMIN through PTRACE_SEIZE or PTRACE_SETOPTIONS.
Signed-off-by: Jann Horn <jannh@google.com>
Co-developed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>

tools/testing/selftests/seccomp/Makefile

 # SPDX-License-Identifier: GPL-2.0
 CFLAGS += -Wl,-no-as-needed -Wall -isystem ../../../../usr/include/
 LDFLAGS += -lpthread
+LDLIBS += -lcap
 
 TEST_GEN_PROGS := seccomp_bpf seccomp_benchmark
 include ../lib.mk

tools/testing/selftests/seccomp/seccomp_bpf.c

@@ -46,6 +46,7 @@
 #include <sys/ioctl.h>
 #include <linux/kcmp.h>
 #include <sys/resource.h>
+#include <sys/capability.h>
 
 #include <unistd.h>
 #include <sys/syscall.h>
@@ -4231,6 +4232,68 @@ TEST(user_notification_addfd_rlimit)
 	close(memfd);
 }
 
+/* Make sure PTRACE_O_SUSPEND_SECCOMP requires CAP_SYS_ADMIN. */
+FIXTURE(O_SUSPEND_SECCOMP) {
+	pid_t pid;
+};
+
+FIXTURE_SETUP(O_SUSPEND_SECCOMP)
+{
+	ERRNO_FILTER(block_read, E2BIG);
+	cap_value_t cap_list[] = { CAP_SYS_ADMIN };
+	cap_t caps;
+
+	self->pid = 0;
+
+	/* make sure we don't have CAP_SYS_ADMIN */
+	caps = cap_get_proc();
+	ASSERT_NE(NULL, caps);
+	ASSERT_EQ(0, cap_set_flag(caps, CAP_EFFECTIVE, 1, cap_list, CAP_CLEAR));
+	ASSERT_EQ(0, cap_set_proc(caps));
+	cap_free(caps);
+
+	ASSERT_EQ(0, prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0));
+	ASSERT_EQ(0, prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog_block_read));
+
+	self->pid = fork();
+	ASSERT_GE(self->pid, 0);
+
+	if (self->pid == 0) {
+		while (1)
+			pause();
+		_exit(127);
+	}
+}
+
+FIXTURE_TEARDOWN(O_SUSPEND_SECCOMP)
+{
+	if (self->pid)
+		kill(self->pid, SIGKILL);
+}
+
+TEST_F(O_SUSPEND_SECCOMP, setoptions)
+{
+	int wstatus;
+
+	ASSERT_EQ(0, ptrace(PTRACE_ATTACH, self->pid, NULL, 0));
+	ASSERT_EQ(self->pid, wait(&wstatus));
+	ASSERT_EQ(-1, ptrace(PTRACE_SETOPTIONS, self->pid, NULL, PTRACE_O_SUSPEND_SECCOMP));
+	if (errno == EINVAL)
+		SKIP(return, "Kernel does not support PTRACE_O_SUSPEND_SECCOMP (missing CONFIG_CHECKPOINT_RESTORE?)");
+	ASSERT_EQ(EPERM, errno);
+}
+
+TEST_F(O_SUSPEND_SECCOMP, seize)
+{
+	int ret;
+
+	ret = ptrace(PTRACE_SEIZE, self->pid, NULL, PTRACE_O_SUSPEND_SECCOMP);
+	ASSERT_EQ(-1, ret);
+	if (errno == EINVAL)
+		SKIP(return, "Kernel does not support PTRACE_O_SUSPEND_SECCOMP (missing CONFIG_CHECKPOINT_RESTORE?)");
+	ASSERT_EQ(EPERM, errno);
+}
+
 /*
  * TODO:
  * - expand NNP testing