#include <linux/compiler_types.h>
#include <linux/preempt.h>
#include <linux/printk.h>
#include <linux/mm.h>
#include <linux/pgtable.h>
#include <linux/uaccess.h>
#include <asm/current.h>
#include <linux/cred.h>
#include <linux/fs.h>
#include <linux/types.h>
#include <linux/version.h>
#include <linux/sched/task_stack.h>
#include <linux/ptrace.h>

#include "allowlist.h"
#include "feature.h"
#include "klog.h" // IWYU pragma: keep
#include "ksud.h"
#include "sucompat.h"
#include "app_profile.h"

#include "sulog.h"

#define SU_PATH "/system/bin/su"
#define SH_PATH "/system/bin/sh"

bool ksu_su_compat_enabled __read_mostly = true;

static int su_compat_feature_get(u64 *value)
{
    *value = ksu_su_compat_enabled ? 1 : 0;
    return 0;
}

static int su_compat_feature_set(u64 value)
{
    bool enable = value != 0;
    ksu_su_compat_enabled = enable;
    pr_info("su_compat: set to %d\n", enable);
    return 0;
}

static const struct ksu_feature_handler su_compat_handler = {
    .feature_id = KSU_FEATURE_SU_COMPAT,
    .name = "su_compat",
    .get_handler = su_compat_feature_get,
    .set_handler = su_compat_feature_set,
};

static void __user *userspace_stack_buffer(const void *d, size_t len)
{
    // To avoid having to mmap a page in userspace, just write below the stack
    // pointer.
    char __user *p = (void __user *)current_user_stack_pointer() - len;

    return copy_to_user(p, d, len) ? NULL : p;
}

static char __user *sh_user_path(void)
{
    static const char sh_path[] = "/system/bin/sh";

    return userspace_stack_buffer(sh_path, sizeof(sh_path));
}

static char __user *ksud_user_path(void)
{
    static const char ksud_path[] = KSUD_PATH;

    return userspace_stack_buffer(ksud_path, sizeof(ksud_path));
}

static bool try_set_access_flag(unsigned long addr)
{
#ifdef CONFIG_ARM64
    struct mm_struct *mm = current->mm;
    struct vm_area_struct *vma;
    pgd_t *pgd;
    p4d_t *p4d;
    pud_t *pud;
    pmd_t *pmd;
    pte_t *ptep, pte;
    spinlock_t *ptl;
    bool ret = false;

    if (!mm)
        return false;

    if (!mmap_read_trylock(mm))
        return false;

    vma = find_vma(mm, addr);
    if (!vma || addr < vma->vm_start)
        goto out_unlock;

    pgd = pgd_offset(mm, addr);
    if (!pgd_present(*pgd))
        goto out_unlock;

    p4d = p4d_offset(pgd, addr);
    if (!p4d_present(*p4d))
        goto out_unlock;

    pud = pud_offset(p4d, addr);
    if (!pud_present(*pud))
        goto out_unlock;

    pmd = pmd_offset(pud, addr);
    if (!pmd_present(*pmd))
        goto out_unlock;

    if (pmd_trans_huge(*pmd))
        goto out_unlock;

    ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
    if (!ptep)
        goto out_unlock;

    pte = *ptep;

    if (!pte_present(pte))
        goto out_pte_unlock;

    if (pte_young(pte)) {
        ret = true;
        goto out_pte_unlock;
    }

    ptep_set_access_flags(vma, addr, ptep, pte_mkyoung(pte), 0);
    pr_info("set AF for addr %lx\n", addr);
    ret = true;

out_pte_unlock:
    pte_unmap_unlock(ptep, ptl);
out_unlock:
    mmap_read_unlock(mm);
    return ret;
#else
    return false;
#endif
}

int ksu_handle_faccessat(int *dfd, const char __user **filename_user, int *mode,
                         int *__unused_flags)
{
    const char su[] = SU_PATH;

    if (!ksu_is_allow_uid_for_current(current_uid().val)) {
        return 0;
    }

    char path[sizeof(su) + 1];
    memset(path, 0, sizeof(path));
    strncpy_from_user_nofault(path, *filename_user, sizeof(path));

    if (unlikely(!memcmp(path, su, sizeof(su)))) {
#if __SULOG_GATE
        ksu_sulog_report_syscall(current_uid().val, NULL, "faccessat", path);
#endif
        pr_info("faccessat su->sh!\n");
        *filename_user = sh_user_path();
    }

    return 0;
}

int ksu_handle_stat(int *dfd, const char __user **filename_user, int *flags)
{
    // const char sh[] = SH_PATH;
    const char su[] = SU_PATH;

    if (!ksu_is_allow_uid_for_current(current_uid().val)) {
        return 0;
    }

    if (unlikely(!filename_user)) {
        return 0;
    }

    char path[sizeof(su) + 1];
    memset(path, 0, sizeof(path));
    strncpy_from_user_nofault(path, *filename_user, sizeof(path));

    if (unlikely(!memcmp(path, su, sizeof(su)))) {
#if __SULOG_GATE
        ksu_sulog_report_syscall(current_uid().val, NULL, "newfstatat", path);
#endif
        pr_info("newfstatat su->sh!\n");
        *filename_user = sh_user_path();
    }

    return 0;
}

int ksu_handle_execve_sucompat(const char __user **filename_user,
                   void *__never_use_argv, void *__never_use_envp,
                   int *__never_use_flags)
{
    const char su[] = SU_PATH;
    const char __user *fn;
    char path[sizeof(su) + 1];
    long ret;
    unsigned long addr;

    if (unlikely(!filename_user))
        return 0;

#if __SULOG_GATE
    bool is_allowed = ksu_is_allow_uid_for_current(current_uid().val);
    ksu_sulog_report_syscall(current_uid().val, NULL, "execve", path);
    
    if (!is_allowed)
        return 0;

    ksu_sulog_report_su_attempt(current_uid().val, NULL, path, is_allowed);
#else
    if (!ksu_is_allow_uid_for_current(current_uid().val)) {
        return 0;
    }
#endif

    addr = untagged_addr((unsigned long)*filename_user);
    fn = (const char __user *)addr;
    memset(path, 0, sizeof(path));
    ret = strncpy_from_user_nofault(path, fn, sizeof(path));

    if (ret < 0 && try_set_access_flag(addr)) {
        ret = strncpy_from_user_nofault(path, fn, sizeof(path));
    }

    if (ret < 0 && preempt_count()) {
        /* This is crazy, but we know what we are doing:
         * Temporarily exit atomic context to handle page faults, then restore it */
        pr_info("Access filename failed, try rescue..\n");
        preempt_enable_no_resched_notrace();
        ret = strncpy_from_user(path, fn, sizeof(path));
        preempt_disable_notrace();
    }

    if (ret < 0) {
        pr_warn("Access filename when execve failed: %ld", ret);
        return 0;
    }

    if (likely(memcmp(path, su, sizeof(su))))
        return 0;

    pr_info("sys_execve su found\n");
    *filename_user = ksud_user_path();

    escape_with_root_profile();
}

// sucompat: permitted process can execute 'su' to gain root access.
void ksu_sucompat_init()
{
    if (ksu_register_feature_handler(&su_compat_handler)) {
        pr_err("Failed to register su_compat feature handler\n");
    }
}

void ksu_sucompat_exit()
{
    ksu_unregister_feature_handler(KSU_FEATURE_SU_COMPAT);
}