Commit d5810139 authored by Frederick Lawler's avatar Frederick Lawler Committed by Paul Moore
Browse files

selftests/bpf: Add tests verifying bpf lsm userns_create hook 



The LSM hook userns_create was introduced to provide LSM's an
opportunity to block or allow unprivileged user namespace creation. This
test serves two purposes: it provides a test eBPF implementation, and
tests the hook successfully blocks or allows user namespace creation.

This tests 3 cases:

        1. Unattached bpf program does not block unpriv user namespace
           creation.
        2. Attached bpf program allows user namespace creation given
           CAP_SYS_ADMIN privileges.
        3. Attached bpf program denies user namespace creation for a
           user without CAP_SYS_ADMIN.

Acked-by: default avatarKP Singh <kpsingh@kernel.org>
Signed-off-by: default avatarFrederick Lawler <fred@cloudflare.com>
Signed-off-by: default avatarPaul Moore <paul@paul-moore.com>
parent 401e64b3

tools/testing/selftests/bpf/prog_tests/deny_namespace.c

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// SPDX-License-Identifier: GPL-2.0

#define _GNU_SOURCE

#include <test_progs.h>

#include "test_deny_namespace.skel.h"

#include <sched.h>

#include "cap_helpers.h"

#include <stdio.h>



static int wait_for_pid(pid_t pid)

{

	int status, ret;



again:

	ret = waitpid(pid, &status, 0);

	if (ret == -1) {

		if (errno == EINTR)

			goto again;



		return -1;

	}



	if (!WIFEXITED(status))

		return -1;



	return WEXITSTATUS(status);

}



/* negative return value -> some internal error

 * positive return value -> userns creation failed

 * 0                     -> userns creation succeeded

 */

static int create_user_ns(void)

{

	pid_t pid;



	pid = fork();

	if (pid < 0)

		return -1;



	if (pid == 0) {

		if (unshare(CLONE_NEWUSER))

			_exit(EXIT_FAILURE);

		_exit(EXIT_SUCCESS);

	}



	return wait_for_pid(pid);

}



static void test_userns_create_bpf(void)

{

	__u32 cap_mask = 1ULL << CAP_SYS_ADMIN;

	__u64 old_caps = 0;



	cap_enable_effective(cap_mask, &old_caps);



	ASSERT_OK(create_user_ns(), "priv new user ns");



	cap_disable_effective(cap_mask, &old_caps);



	ASSERT_EQ(create_user_ns(), EPERM, "unpriv new user ns");



	if (cap_mask & old_caps)

		cap_enable_effective(cap_mask, NULL);

}



static void test_unpriv_userns_create_no_bpf(void)

{

	__u32 cap_mask = 1ULL << CAP_SYS_ADMIN;

	__u64 old_caps = 0;



	cap_disable_effective(cap_mask, &old_caps);



	ASSERT_OK(create_user_ns(), "no-bpf unpriv new user ns");



	if (cap_mask & old_caps)

		cap_enable_effective(cap_mask, NULL);

}



void test_deny_namespace(void)

{

	struct test_deny_namespace *skel = NULL;

	int err;



	if (test__start_subtest("unpriv_userns_create_no_bpf"))

		test_unpriv_userns_create_no_bpf();



	skel = test_deny_namespace__open_and_load();

	if (!ASSERT_OK_PTR(skel, "skel load"))

		goto close_prog;



	err = test_deny_namespace__attach(skel);

	if (!ASSERT_OK(err, "attach"))

		goto close_prog;



	if (test__start_subtest("userns_create_bpf"))

		test_userns_create_bpf();



	test_deny_namespace__detach(skel);



close_prog:

	test_deny_namespace__destroy(skel);

}

tools/testing/selftests/bpf/progs/test_deny_namespace.c

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// SPDX-License-Identifier: GPL-2.0

#include <linux/bpf.h>

#include <bpf/bpf_helpers.h>

#include <bpf/bpf_tracing.h>

#include <errno.h>

#include <linux/capability.h>



struct kernel_cap_struct {

	__u32 cap[_LINUX_CAPABILITY_U32S_3];

} __attribute__((preserve_access_index));



struct cred {

	struct kernel_cap_struct cap_effective;

} __attribute__((preserve_access_index));



char _license[] SEC("license") = "GPL";



SEC("lsm.s/userns_create")

int BPF_PROG(test_userns_create, const struct cred *cred, int ret)

{

	struct kernel_cap_struct caps = cred->cap_effective;

	int cap_index = CAP_TO_INDEX(CAP_SYS_ADMIN);

	__u32 cap_mask = CAP_TO_MASK(CAP_SYS_ADMIN);



	if (ret)

		return 0;



	ret = -EPERM;

	if (caps.cap[cap_index] & cap_mask)

		return 0;



	return -EPERM;

}