[PATCH v3 6/9] selftests/bpf: Check if the digest is refreshed after a file write

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

Verify that bpf_ima_inode_hash() returns a non-fresh digest after a file
write, and that bpf_ima_file_hash() returns a fresh digest. Verification is
done by requesting the digest from the bprm_creds_for_exec hook, called
before ima_bprm_check().

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
tools/testing/selftests/bpf/ima_setup.sh | 24 ++++++-
.../selftests/bpf/prog_tests/test_ima.c | 72 ++++++++++++++++++-
tools/testing/selftests/bpf/progs/ima.c | 11 +++
3 files changed, 103 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/bpf/ima_setup.sh b/tools/testing/selftests/bpf/ima_setup.sh
index 8e62581113a3..a3de1cd43ba0 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> <existing_tmp_dir>"
+ echo "Usage: $0 <setup|cleanup|run|modify-bin|restore-bin> <existing_tmp_dir>"
exit 1
}

@@ -77,6 +77,24 @@ run()
exec "${copied_bin_path}"
}

+modify_bin()
+{
+ local tmp_dir="$1"
+ local mount_dir="${tmp_dir}/mnt"
+ local copied_bin_path="${mount_dir}/$(basename ${TEST_BINARY})"
+
+ echo "mod" >> "${copied_bin_path}"
+}
+
+restore_bin()
+{
+ local tmp_dir="$1"
+ local mount_dir="${tmp_dir}/mnt"
+ local copied_bin_path="${mount_dir}/$(basename ${TEST_BINARY})"
+
+ truncate -s -4 "${copied_bin_path}"
+}
+
catch()
{
local exit_code="$1"
@@ -105,6 +123,10 @@ main()
cleanup "${tmp_dir}"
elif [[ "${action}" == "run" ]]; then
run "${tmp_dir}"
+ elif [[ "${action}" == "modify-bin" ]]; then
+ modify_bin "${tmp_dir}"
+ elif [[ "${action}" == "restore-bin" ]]; then
+ restore_bin "${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 acc911ba63fd..a0cfba0b4273 100644
--- a/tools/testing/selftests/bpf/prog_tests/test_ima.c
+++ b/tools/testing/selftests/bpf/prog_tests/test_ima.c
@@ -13,16 +13,17 @@

#include "ima.skel.h"

-#define MAX_SAMPLES 2
+#define MAX_SAMPLES 4

-static int run_measured_process(const char *measured_dir, u32 *monitored_pid)
+static int _run_measured_process(const char *measured_dir, u32 *monitored_pid,
+ const char *cmd)
{
int child_pid, child_status;

child_pid = fork();
if (child_pid == 0) {
*monitored_pid = getpid();
- execlp("./ima_setup.sh", "./ima_setup.sh", "run", measured_dir,
+ execlp("./ima_setup.sh", "./ima_setup.sh", cmd, measured_dir,
NULL);
exit(errno);

@@ -34,6 +35,11 @@ static int run_measured_process(const char *measured_dir, u32 *monitored_pid)
return -EINVAL;
}

+static int run_measured_process(const char *measured_dir, u32 *monitored_pid)
+{
+ return _run_measured_process(measured_dir, monitored_pid, "run");
+}
+
static u64 ima_hash_from_bpf[MAX_SAMPLES];
static int ima_hash_from_bpf_idx;

@@ -51,6 +57,7 @@ static void test_init(struct ima__bss *bss)
ima_hash_from_bpf_idx = 0;

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

void test_test_ima(void)
@@ -58,6 +65,7 @@ void test_test_ima(void)
char measured_dir_template[] = "/tmp/ima_measuredXXXXXX";
struct ring_buffer *ringbuf = NULL;
const char *measured_dir;
+ u64 bin_true_sample;
char cmd[256];

int err, duration = 0;
@@ -114,6 +122,64 @@ void test_test_ima(void)
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");
+ bin_true_sample = ima_hash_from_bpf[1];
+
+ /*
+ * Test #3
+ * - Goal: confirm that bpf_ima_inode_hash() returns a non-fresh digest
+ * - Expected result: 2 samples (/bin/true: non-fresh, fresh)
+ */
+ test_init(skel->bss);
+
+ err = _run_measured_process(measured_dir, &skel->bss->monitored_pid,
+ "modify-bin");
+ if (CHECK(err, "modify-bin #3", "err = %d\n", err))
+ goto close_clean;
+
+ skel->bss->enable_bprm_creds_for_exec = true;
+ err = run_measured_process(measured_dir, &skel->bss->monitored_pid);
+ if (CHECK(err, "run_measured_process #3", "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");
+ ASSERT_EQ(ima_hash_from_bpf[0], bin_true_sample, "sample_equal_or_err");
+ /* IMA refreshed the digest. */
+ ASSERT_NEQ(ima_hash_from_bpf[1], bin_true_sample,
+ "sample_different_or_err");
+
+ /*
+ * Test #4
+ * - Goal: verify that bpf_ima_file_hash() returns a fresh digest
+ * - Expected result: 4 samples (./ima_setup.sh: fresh, fresh;
+ * /bin/true: fresh, fresh)
+ */
+ test_init(skel->bss);
+ skel->bss->use_ima_file_hash = true;
+ skel->bss->enable_bprm_creds_for_exec = true;
+ err = run_measured_process(measured_dir, &skel->bss->monitored_pid);
+ if (CHECK(err, "run_measured_process #4", "err = %d\n", err))
+ goto close_clean;
+
+ err = ring_buffer__consume(ringbuf);
+ ASSERT_EQ(err, 4, "num_samples_or_err");
+ ASSERT_NEQ(ima_hash_from_bpf[0], 0, "ima_hash");
+ ASSERT_NEQ(ima_hash_from_bpf[1], 0, "ima_hash");
+ ASSERT_NEQ(ima_hash_from_bpf[2], 0, "ima_hash");
+ ASSERT_NEQ(ima_hash_from_bpf[3], 0, "ima_hash");
+ ASSERT_NEQ(ima_hash_from_bpf[2], bin_true_sample,
+ "sample_different_or_err");
+ ASSERT_EQ(ima_hash_from_bpf[3], ima_hash_from_bpf[2],
+ "sample_equal_or_err");
+
+ skel->bss->use_ima_file_hash = false;
+ skel->bss->enable_bprm_creds_for_exec = false;
+ err = _run_measured_process(measured_dir, &skel->bss->monitored_pid,
+ "restore-bin");
+ if (CHECK(err, "restore-bin #3", "err = %d\n", err))
+ goto close_clean;

close_clean:
snprintf(cmd, sizeof(cmd), "./ima_setup.sh cleanup %s", measured_dir);
diff --git a/tools/testing/selftests/bpf/progs/ima.c b/tools/testing/selftests/bpf/progs/ima.c
index e0b073dcfb5d..9633e5f2453d 100644
--- a/tools/testing/selftests/bpf/progs/ima.c
+++ b/tools/testing/selftests/bpf/progs/ima.c
@@ -19,6 +19,7 @@ struct {
char _license[] SEC("license") = "GPL";

bool use_ima_file_hash;
+bool enable_bprm_creds_for_exec;

static void ima_test_common(struct file *file)
{
@@ -54,3 +55,13 @@ void BPF_PROG(bprm_committed_creds, struct linux_binprm *bprm)
{
ima_test_common(bprm->file);
}
+
+SEC("lsm.s/bprm_creds_for_exec")
+int BPF_PROG(bprm_creds_for_exec, struct linux_binprm *bprm)
+{
+ if (!enable_bprm_creds_for_exec)
+ return 0;
+
+ ima_test_common(bprm->file);
+ return 0;
+}
--
2.32.0