kernel_compat.c

#include <linux/version.h>
#include <linux/fs.h>
#include <linux/nsproxy.h>
#include <linux/sched/task.h>
#include <linux/uaccess.h>
#include "klog.h" // IWYU pragma: keep
#include "kernel_compat.h"

extern struct task_struct init_task;

// mnt_ns context switch for environment that android_init->nsproxy->mnt_ns != init_task.nsproxy->mnt_ns, such as WSA
struct ksu_ns_fs_saved {
	struct nsproxy *ns;
	struct fs_struct *fs;
};

static void ksu_save_ns_fs(struct ksu_ns_fs_saved *ns_fs_saved)
{
	ns_fs_saved->ns = current->nsproxy;
	ns_fs_saved->fs = current->fs;
}

static void ksu_load_ns_fs(struct ksu_ns_fs_saved *ns_fs_saved)
{
	current->nsproxy = ns_fs_saved->ns;
	current->fs = ns_fs_saved->fs;
}

static bool android_context_saved_checked = false;
static bool android_context_saved_enabled = false;
static struct ksu_ns_fs_saved android_context_saved;

void ksu_android_ns_fs_check()
{
	if (android_context_saved_checked)
		return;
	android_context_saved_checked = true;
	task_lock(current);
	if (current->nsproxy && current->fs &&
	    current->nsproxy->mnt_ns != init_task.nsproxy->mnt_ns) {
		android_context_saved_enabled = true;
		pr_info("android context saved enabled due to init mnt_ns(%p) != android mnt_ns(%p)\n",
			current->nsproxy->mnt_ns, init_task.nsproxy->mnt_ns);
		ksu_save_ns_fs(&android_context_saved);
	} else {
		pr_info("android context saved disabled\n");
	}
	task_unlock(current);
}

struct file *ksu_filp_open_compat(const char *filename, int flags, umode_t mode)
{
	// switch mnt_ns even if current is not wq_worker, to ensure what we open is the correct file in android mnt_ns, rather than user created mnt_ns
	struct ksu_ns_fs_saved saved;
	if (android_context_saved_enabled) {
		pr_info("start switch current nsproxy and fs to android context\n");
		task_lock(current);
		ksu_save_ns_fs(&saved);
		ksu_load_ns_fs(&android_context_saved);
		task_unlock(current);
	}
	struct file *fp = filp_open(filename, flags, mode);
	if (android_context_saved_enabled) {
		task_lock(current);
		ksu_load_ns_fs(&saved);
		task_unlock(current);
		pr_info("switch current nsproxy and fs back to saved successfully\n");
	}
	return fp;
}

ssize_t ksu_kernel_read_compat(struct file *p, void *buf, size_t count,
			       loff_t *pos)
{
	return kernel_read(p, buf, count, pos);
}

ssize_t ksu_kernel_write_compat(struct file *p, const void *buf, size_t count,
				loff_t *pos)
{
	return kernel_write(p, buf, count, pos);
}

long ksu_strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
				   long count)
{
	return strncpy_from_user_nofault(dst, unsafe_addr, count);
}