[PATCH v3 8/9] selftests/bpf: Add test for bpf_lsm_kernel_read_file()

Roberto Sassu
2022-03-02T11:18:20Z

Test the ability of bpf_lsm_kernel_read_file() to call the sleepable
functions bpf_ima_inode_hash() or bpf_ima_file_hash() to obtain a
measurement of a loaded IMA policy.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
tools/testing/selftests/bpf/ima_setup.sh | 13 ++++++++++++-
.../selftests/bpf/prog_tests/test_ima.c | 19 +++++++++++++++++++
tools/testing/selftests/bpf/progs/ima.c | 18 ++++++++++++++++++
3 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/ima_setup.sh b/tools/testing/selftests/bpf/ima_setup.sh
index a3de1cd43ba0..8ecead4ccad0 100755
--- a/tools/testing/selftests/bpf/ima_setup.sh
+++ b/tools/testing/selftests/bpf/ima_setup.sh
@@ -12,7 +12,7 @@ LOG_FILE="$(mktemp /tmp/ima_setup.XXXX.log)"

usage()
{
- echo "Usage: $0 <setup|cleanup|run|modify-bin|restore-bin> <existing_tmp_dir>"
+ echo "Usage: $0 <setup|cleanup|run|modify-bin|restore-bin|load-policy> <existing_tmp_dir>"
exit 1
}

@@ -51,6 +51,7 @@ setup()

ensure_mount_securityfs
echo "measure func=BPRM_CHECK fsuuid=${mount_uuid}" > ${IMA_POLICY_FILE}
+ echo "measure func=BPRM_CHECK fsuuid=${mount_uuid}" > ${mount_dir}/policy_test
}

cleanup() {
@@ -95,6 +96,14 @@ restore_bin()
truncate -s -4 "${copied_bin_path}"
}

+load_policy()
+{
+ local tmp_dir="$1"
+ local mount_dir="${tmp_dir}/mnt"
+
+ echo ${mount_dir}/policy_test > ${IMA_POLICY_FILE} 2> /dev/null
+}
+
catch()
{
local exit_code="$1"
@@ -127,6 +136,8 @@ main()
modify_bin "${tmp_dir}"
elif [[ "${action}" == "restore-bin" ]]; then
restore_bin "${tmp_dir}"
+ elif [[ "${action}" == "load-policy" ]]; then
+ load_policy "${tmp_dir}"
else
echo "Unknown action: ${action}"
exit 1
diff --git a/tools/testing/selftests/bpf/prog_tests/test_ima.c b/tools/testing/selftests/bpf/prog_tests/test_ima.c
index a0cfba0b4273..b13a141c4220 100644
--- a/tools/testing/selftests/bpf/prog_tests/test_ima.c
+++ b/tools/testing/selftests/bpf/prog_tests/test_ima.c
@@ -58,6 +58,7 @@ static void test_init(struct ima__bss *bss)

bss->use_ima_file_hash = false;
bss->enable_bprm_creds_for_exec = false;
+ bss->enable_kernel_read_file = false;
}

void test_test_ima(void)
@@ -181,6 +182,24 @@ void test_test_ima(void)
if (CHECK(err, "restore-bin #3", "err = %d\n", err))
goto close_clean;

+ /*
+ * Test #5
+ * - Goal: obtain a sample from the kernel_read_file hook
+ * - Expected result: 2 samples (./ima_setup.sh, policy_test)
+ */
+ test_init(skel->bss);
+ skel->bss->use_ima_file_hash = true;
+ skel->bss->enable_kernel_read_file = true;
+ err = _run_measured_process(measured_dir, &skel->bss->monitored_pid,
+ "load-policy");
+ if (CHECK(err, "run_measured_process #5", "err = %d\n", err))
+ goto close_clean;
+
+ err = ring_buffer__consume(ringbuf);
+ ASSERT_EQ(err, 2, "num_samples_or_err");
+ ASSERT_NEQ(ima_hash_from_bpf[0], 0, "ima_hash");
+ ASSERT_NEQ(ima_hash_from_bpf[1], 0, "ima_hash");
+
close_clean:
snprintf(cmd, sizeof(cmd), "./ima_setup.sh cleanup %s", measured_dir);
err = system(cmd);
diff --git a/tools/testing/selftests/bpf/progs/ima.c b/tools/testing/selftests/bpf/progs/ima.c
index 9633e5f2453d..e3ce943c5c3d 100644
--- a/tools/testing/selftests/bpf/progs/ima.c
+++ b/tools/testing/selftests/bpf/progs/ima.c
@@ -20,6 +20,7 @@ char _license[] SEC("license") = "GPL";

bool use_ima_file_hash;
bool enable_bprm_creds_for_exec;
+bool enable_kernel_read_file;

static void ima_test_common(struct file *file)
{
@@ -65,3 +66,20 @@ int BPF_PROG(bprm_creds_for_exec, struct linux_binprm *bprm)
ima_test_common(bprm->file);
return 0;
}
+
+SEC("lsm.s/kernel_read_file")
+int BPF_PROG(kernel_read_file, struct file *file, enum kernel_read_file_id id,
+ bool contents)
+{
+ if (!enable_kernel_read_file)
+ return 0;
+
+ if (!contents)
+ return 0;
+
+ if (id != READING_POLICY)
+ return 0;
+
+ ima_test_common(file);
+ return 0;
+}
--
2.32.0