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// SPDX-License-Identifier: GPL-2.0-only
/*
* ntsync.c - Kernel driver for NT synchronization primitives
*
* Copyright (C) 2024 Elizabeth Figura <zfigura@codeweavers.com>
*/
#include <linux/anon_inodes.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
#include <linux/overflow.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <uapi/linux/ntsync.h>
#define NTSYNC_NAME "ntsync"
enum ntsync_type {
NTSYNC_TYPE_SEM,
};
/*
* Individual synchronization primitives are represented by
* struct ntsync_obj, and each primitive is backed by a file.
*
* The whole namespace is represented by a struct ntsync_device also
* backed by a file.
*
* Both rely on struct file for reference counting. Individual
* ntsync_obj objects take a reference to the device when created.
*/
struct ntsync_obj {
spinlock_t lock;
enum ntsync_type type;
struct file *file;
struct ntsync_device *dev;
/* The following fields are protected by the object lock. */
union {
struct {
__u32 count;
__u32 max;
} sem;
} u;
};
struct ntsync_device {
struct file *file;
};
/*
* Actually change the semaphore state, returning -EOVERFLOW if it is made
* invalid.
*/
static int post_sem_state(struct ntsync_obj *sem, __u32 count)
{
__u32 sum;
lockdep_assert_held(&sem->lock);
if (check_add_overflow(sem->u.sem.count, count, &sum) ||
sum > sem->u.sem.max)
return -EOVERFLOW;
sem->u.sem.count = sum;
return 0;
}
static int ntsync_sem_post(struct ntsync_obj *sem, void __user *argp)
{
__u32 __user *user_args = argp;
__u32 prev_count;
__u32 args;
int ret;
if (copy_from_user(&args, argp, sizeof(args)))
return -EFAULT;
if (sem->type != NTSYNC_TYPE_SEM)
return -EINVAL;
spin_lock(&sem->lock);
prev_count = sem->u.sem.count;
ret = post_sem_state(sem, args);
spin_unlock(&sem->lock);
if (!ret && put_user(prev_count, user_args))
ret = -EFAULT;
return ret;
}
static int ntsync_obj_release(struct inode *inode, struct file *file)
{
struct ntsync_obj *obj = file->private_data;
fput(obj->dev->file);
kfree(obj);
return 0;
}
static long ntsync_obj_ioctl(struct file *file, unsigned int cmd,
unsigned long parm)
{
struct ntsync_obj *obj = file->private_data;
void __user *argp = (void __user *)parm;
switch (cmd) {
case NTSYNC_IOC_SEM_POST:
return ntsync_sem_post(obj, argp);
default:
return -ENOIOCTLCMD;
}
}
static const struct file_operations ntsync_obj_fops = {
.owner = THIS_MODULE,
.release = ntsync_obj_release,
.unlocked_ioctl = ntsync_obj_ioctl,
.compat_ioctl = compat_ptr_ioctl,
};
static struct ntsync_obj *ntsync_alloc_obj(struct ntsync_device *dev,
enum ntsync_type type)
{
struct ntsync_obj *obj;
obj = kzalloc(sizeof(*obj), GFP_KERNEL);
if (!obj)
return NULL;
obj->type = type;
obj->dev = dev;
get_file(dev->file);
spin_lock_init(&obj->lock);
return obj;
}
static int ntsync_obj_get_fd(struct ntsync_obj *obj)
{
struct file *file;
int fd;
fd = get_unused_fd_flags(O_CLOEXEC);
if (fd < 0)
return fd;
file = anon_inode_getfile("ntsync", &ntsync_obj_fops, obj, O_RDWR);
if (IS_ERR(file)) {
put_unused_fd(fd);
return PTR_ERR(file);
}
obj->file = file;
fd_install(fd, file);
return fd;
}
static int ntsync_create_sem(struct ntsync_device *dev, void __user *argp)
{
struct ntsync_sem_args __user *user_args = argp;
struct ntsync_sem_args args;
struct ntsync_obj *sem;
int fd;
if (copy_from_user(&args, argp, sizeof(args)))
return -EFAULT;
if (args.count > args.max)
return -EINVAL;
sem = ntsync_alloc_obj(dev, NTSYNC_TYPE_SEM);
if (!sem)
return -ENOMEM;
sem->u.sem.count = args.count;
sem->u.sem.max = args.max;
fd = ntsync_obj_get_fd(sem);
if (fd < 0) {
kfree(sem);
return fd;
}
return put_user(fd, &user_args->sem);
}
static int ntsync_char_open(struct inode *inode, struct file *file)
{
struct ntsync_device *dev;
dev = kzalloc(sizeof(*dev), GFP_KERNEL);
if (!dev)
return -ENOMEM;
file->private_data = dev;
dev->file = file;
return nonseekable_open(inode, file);
}
static int ntsync_char_release(struct inode *inode, struct file *file)
{
struct ntsync_device *dev = file->private_data;
kfree(dev);
return 0;
}
static long ntsync_char_ioctl(struct file *file, unsigned int cmd,
unsigned long parm)
{
struct ntsync_device *dev = file->private_data;
void __user *argp = (void __user *)parm;
switch (cmd) {
case NTSYNC_IOC_CREATE_SEM:
return ntsync_create_sem(dev, argp);
default:
return -ENOIOCTLCMD;
}
}
static const struct file_operations ntsync_fops = {
.owner = THIS_MODULE,
.open = ntsync_char_open,
.release = ntsync_char_release,
.unlocked_ioctl = ntsync_char_ioctl,
.compat_ioctl = compat_ptr_ioctl,
};
static struct miscdevice ntsync_misc = {
.minor = MISC_DYNAMIC_MINOR,
.name = NTSYNC_NAME,
.fops = &ntsync_fops,
};
module_misc_device(ntsync_misc);
MODULE_AUTHOR("Elizabeth Figura <zfigura@codeweavers.com>");
MODULE_DESCRIPTION("Kernel driver for NT synchronization primitives");
MODULE_LICENSE("GPL");
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