/*
 * eset_wap (ESET Web Access Protection module)
 * Copyright (C) 1992-2023 ESET, spol. s r.o.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 *
 * In case of any questions, you can contact us at ESET, spol. s r.o., Einsteinova 24, 851 01 Bratislava, Slovakia.
 */

#include "ewap_path.h"
#include "ewap_helpers.h"

#include <linux/cred.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/version.h>

#if LINUX_VERSION_CODE < KERNEL_VERSION(5, 8, 0)
#define ewap_mm_lock(m) down_read(&(m)->mmap_sem)
#define ewap_mm_unlock(m) up_read(&(m)->mmap_sem)
#else
#define ewap_mm_lock(m) mmap_read_lock(m)
#define ewap_mm_unlock(m) mmap_read_unlock(m)
#endif

static struct kmem_cache *ewap_path_allocator = NULL;

int ewap_path_allocator_init(void) {
  ewap_path_allocator = kmem_cache_create(
      "ewap_path_allocator", sizeof(struct ewap_path),
      __alignof__(struct ewap_path), SLAB_RECLAIM_ACCOUNT, NULL);

  if (!ewap_path_allocator) {
    return -ENOMEM;
  }

  return 0;
}

void ewap_path_allocator_deinit(void) {
  if (ewap_path_allocator) {
    kmem_cache_destroy(ewap_path_allocator);
  }
}

static struct ewap_path *ewap_path_alloc(void) {
  struct ewap_path *result = kmem_cache_zalloc(ewap_path_allocator, GFP_KERNEL);
  if (unlikely(!result)) {
    return NULL;
  }

  result->size = PATH_MAX;
  result->buf = kzalloc(result->size, GFP_KERNEL);

  if (unlikely(!result->buf)) {
    kmem_cache_free(ewap_path_allocator, result);
    return NULL;
  }

  atomic_set(&result->count, 1);
  return result;
}

static void ewap_path_free(struct ewap_path *path) {
  if (path) {
    ewap_pr_log(EWAP_LOG_CONNECTIONS, "ewap_path deleted %s", path->ptr);

    kfree(path->buf);
    kmem_cache_free(ewap_path_allocator, path);
  }
}

struct ewap_path *ewap_path_new(void) {
  char *tmp;
  struct ewap_path *result;
  struct mm_struct *mm = current->mm;

  if (unlikely(!mm)) {
    return ERR_PTR(-ENODATA);
  }

  result = ewap_path_alloc();
  if (unlikely(!result)) {
    return ERR_PTR(-ENOMEM);
  }

  ewap_mm_lock(mm);
  if (likely(mm->exe_file)) {
    tmp = d_path(&mm->exe_file->f_path, result->buf, result->size);
  } else {
    tmp = ERR_PTR(-ENODATA);
  }
  ewap_mm_unlock(mm);

  if (IS_ERR(tmp)) {
    int err = PTR_ERR(tmp);
    ewap_path_free(result);
    return ERR_PTR(err);
  }

  result->ptr = tmp;
  result->size = strlen(tmp) + 1;

  ewap_pr_log(EWAP_LOG_CONNECTIONS, "ewap_path created %s", result->ptr);

  return result;
}

struct ewap_path *ewap_path_ref(struct ewap_path *path) {
  if (!path || IS_ERR(path)) return NULL;

  BUG_ON(!atomic_read(&path->count));
  atomic_inc(&path->count);

  return path;
}

void ewap_path_unref(struct ewap_path *path) {
  if (!path || IS_ERR(path)) return;

  BUG_ON(!atomic_read(&path->count));

  if (!atomic_dec_and_test(&path->count)) return;

  ewap_path_free(path);
}