bpf: Add a selftest for bpf_ima_inode_hash

The test does the following:

- Mounts a loopback filesystem and appends the IMA policy to measure
  executions only on this file-system. Restricting the IMA policy to
  a particular filesystem prevents a system-wide IMA policy change.
- Executes an executable copied to this loopback filesystem.
- Calls the bpf_ima_inode_hash in the bprm_committed_creds hook and
  checks if the call succeeded and checks if a hash was calculated.

The test shells out to the added ima_setup.sh script as the setup is
better handled in a shell script and is more complicated to do in the
test program or even shelling out individual commands from C.

The list of required configs (i.e. IMA, SECURITYFS,
IMA_{WRITE,READ}_POLICY) for running this test are also updated.

Suggested-by: Mimi Zohar <zohar@linux.ibm.com> (limit policy rule to loopback mount)
Signed-off-by: KP Singh <kpsingh@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20201124151210.1081188-4-kpsingh@chromium.org

tools/testing/selftests/bpf/config

@@ -39,3 +39,7 @@ CONFIG_BPF_JIT=y
 CONFIG_BPF_LSM=y
 CONFIG_SECURITY=y
 CONFIG_LIRC=y
+CONFIG_IMA=y
+CONFIG_SECURITYFS=y
+CONFIG_IMA_WRITE_POLICY=y
+CONFIG_IMA_READ_POLICY=y

tools/testing/selftests/bpf/ima_setup.sh

+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+set -e
+set -u
+
+IMA_POLICY_FILE="/sys/kernel/security/ima/policy"
+TEST_BINARY="/bin/true"
+
+usage()
+{
+        echo "Usage: $0 <setup|cleanup|run> <existing_tmp_dir>"
+        exit 1
+}
+
+setup()
+{
+        local tmp_dir="$1"
+        local mount_img="${tmp_dir}/test.img"
+        local mount_dir="${tmp_dir}/mnt"
+        local copied_bin_path="${mount_dir}/$(basename ${TEST_BINARY})"
+        mkdir -p ${mount_dir}
+
+        dd if=/dev/zero of="${mount_img}" bs=1M count=10
+
+        local loop_device="$(losetup --find --show ${mount_img})"
+
+        mkfs.ext4 "${loop_device}"
+        mount "${loop_device}" "${mount_dir}"
+
+        cp "${TEST_BINARY}" "${mount_dir}"
+        local mount_uuid="$(blkid -s UUID -o value ${loop_device})"
+        echo "measure func=BPRM_CHECK fsuuid=${mount_uuid}" > ${IMA_POLICY_FILE}
+}
+
+cleanup() {
+        local tmp_dir="$1"
+        local mount_img="${tmp_dir}/test.img"
+        local mount_dir="${tmp_dir}/mnt"
+
+        local loop_devices=$(losetup -j ${mount_img} -O NAME --noheadings)
+        for loop_dev in "${loop_devices}"; do
+                losetup -d $loop_dev
+        done
+
+        umount ${mount_dir}
+        rm -rf ${tmp_dir}
+}
+
+run()
+{
+        local tmp_dir="$1"
+        local mount_dir="${tmp_dir}/mnt"
+        local copied_bin_path="${mount_dir}/$(basename ${TEST_BINARY})"
+
+        exec "${copied_bin_path}"
+}
+
+main()
+{
+        [[ $# -ne 2 ]] && usage
+
+        local action="$1"
+        local tmp_dir="$2"
+
+        [[ ! -d "${tmp_dir}" ]] && echo "Directory ${tmp_dir} doesn't exist" && exit 1
+
+        if [[ "${action}" == "setup" ]]; then
+                setup "${tmp_dir}"
+        elif [[ "${action}" == "cleanup" ]]; then
+                cleanup "${tmp_dir}"
+        elif [[ "${action}" == "run" ]]; then
+                run "${tmp_dir}"
+        else
+                echo "Unknown action: ${action}"
+                exit 1
+        fi
+}
+
+main "$@"

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

+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright (C) 2020 Google LLC.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/wait.h>
+#include <test_progs.h>
+
+#include "ima.skel.h"
+
+static int run_measured_process(const char *measured_dir, u32 *monitored_pid)
+{
+	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,
+		       NULL);
+		exit(errno);
+
+	} else if (child_pid > 0) {
+		waitpid(child_pid, &child_status, 0);
+		return WEXITSTATUS(child_status);
+	}
+
+	return -EINVAL;
+}
+
+void test_test_ima(void)
+{
+	char measured_dir_template[] = "/tmp/ima_measuredXXXXXX";
+	const char *measured_dir;
+	char cmd[256];
+
+	int err, duration = 0;
+	struct ima *skel = NULL;
+
+	skel = ima__open_and_load();
+	if (CHECK(!skel, "skel_load", "skeleton failed\n"))
+		goto close_prog;
+
+	err = ima__attach(skel);
+	if (CHECK(err, "attach", "attach failed: %d\n", err))
+		goto close_prog;
+
+	measured_dir = mkdtemp(measured_dir_template);
+	if (CHECK(measured_dir == NULL, "mkdtemp", "err %d\n", errno))
+		goto close_prog;
+
+	snprintf(cmd, sizeof(cmd), "./ima_setup.sh setup %s", measured_dir);
+	if (CHECK_FAIL(system(cmd)))
+		goto close_clean;
+
+	err = run_measured_process(measured_dir, &skel->bss->monitored_pid);
+	if (CHECK(err, "run_measured_process", "err = %d\n", err))
+		goto close_clean;
+
+	CHECK(skel->data->ima_hash_ret < 0, "ima_hash_ret",
+	      "ima_hash_ret = %ld\n", skel->data->ima_hash_ret);
+
+	CHECK(skel->bss->ima_hash == 0, "ima_hash",
+	      "ima_hash = %lu\n", skel->bss->ima_hash);
+
+close_clean:
+	snprintf(cmd, sizeof(cmd), "./ima_setup.sh cleanup %s", measured_dir);
+	CHECK_FAIL(system(cmd));
+close_prog:
+	ima__destroy(skel);
+}

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

+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright 2020 Google LLC.
+ */
+
+#include "vmlinux.h"
+#include <errno.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+long ima_hash_ret = -1;
+u64 ima_hash = 0;
+u32 monitored_pid = 0;
+
+char _license[] SEC("license") = "GPL";
+
+SEC("lsm.s/bprm_committed_creds")
+int BPF_PROG(ima, struct linux_binprm *bprm)
+{
+	u32 pid = bpf_get_current_pid_tgid() >> 32;
+
+	if (pid == monitored_pid)
+		ima_hash_ret = bpf_ima_inode_hash(bprm->file->f_inode,
+						  &ima_hash, sizeof(ima_hash));
+
+	return 0;
+}