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: KP Singh kpsingh@kernel.org Signed-off-by: Frederick Lawler fred@cloudflare.com
--- The generic deny_namespace file name is used for future namespace expansion. I didn't want to limit these files to just the create_user_ns hook. Changes since v4: - None Changes since v3: - Explicitly set CAP_SYS_ADMIN to test namespace is created given permission - Simplify BPF test to use sleepable hook only - Prefer unshare() over clone() for tests Changes since v2: - Rename create_user_ns hook to userns_create Changes since v1: - Introduce this patch --- .../selftests/bpf/prog_tests/deny_namespace.c | 102 ++++++++++++++++++ .../selftests/bpf/progs/test_deny_namespace.c | 33 ++++++ 2 files changed, 135 insertions(+) create mode 100644 tools/testing/selftests/bpf/prog_tests/deny_namespace.c create mode 100644 tools/testing/selftests/bpf/progs/test_deny_namespace.c
diff --git a/tools/testing/selftests/bpf/prog_tests/deny_namespace.c b/tools/testing/selftests/bpf/prog_tests/deny_namespace.c new file mode 100644 index 000000000000..1bc6241b755b --- /dev/null +++ b/tools/testing/selftests/bpf/prog_tests/deny_namespace.c @@ -0,0 +1,102 @@ +// 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); +} diff --git a/tools/testing/selftests/bpf/progs/test_deny_namespace.c b/tools/testing/selftests/bpf/progs/test_deny_namespace.c new file mode 100644 index 000000000000..09ad5a4ebd1f --- /dev/null +++ b/tools/testing/selftests/bpf/progs/test_deny_namespace.c @@ -0,0 +1,33 @@ +// 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; +}