// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2023 Meta Platforms, Inc. and affiliates. */

#include "vmlinux.h"
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
#include "bpf_kfuncs.h"

char _license[] SEC("license") = "GPL";

#ifndef SHA256_DIGEST_SIZE
#define SHA256_DIGEST_SIZE      32
#endif

#define SIZEOF_STRUCT_FSVERITY_DIGEST 4  /* sizeof(struct fsverity_digest) */

char expected_digest[SIZEOF_STRUCT_FSVERITY_DIGEST + SHA256_DIGEST_SIZE];
char digest[SIZEOF_STRUCT_FSVERITY_DIGEST + SHA256_DIGEST_SIZE];
__u32 monitored_pid;
__u32 got_fsverity;
__u32 digest_matches;

SEC("lsm.s/file_open")
int BPF_PROG(test_file_open, struct file *f)
{
        struct bpf_dynptr digest_ptr;
        __u32 pid;
        int ret;
        int i;

        pid = bpf_get_current_pid_tgid() >> 32;
        if (pid != monitored_pid)
                return 0;

        bpf_dynptr_from_mem(digest, sizeof(digest), 0, &digest_ptr);
        ret = bpf_get_fsverity_digest(f, &digest_ptr);
        if (ret < 0)
                return 0;
        got_fsverity = 1;

        for (i = 0; i < (int)sizeof(digest); i++) {
                if (digest[i] != expected_digest[i])
                        return 0;
        }

        digest_matches = 1;
        return 0;
}