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    Subject[PATCH v5 3/4] selftests/bpf: Add tests verifying bpf lsm userns_create hook
    Date
    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;
    +}
    --
    2.30.2
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