drivers/misc/ntsync.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * ntsync.c - Kernel driver for NT synchronization primitives
   4  *
   5  * Copyright (C) 2024 Elizabeth Figura <zfigura@codeweavers.com>
   6  */
   7
   8 #include <linux/anon_inodes.h>
   9 #include <linux/file.h>
  10 #include <linux/fs.h>
  11 #include <linux/miscdevice.h>
  12 #include <linux/module.h>
  13 #include <linux/overflow.h>
  14 #include <linux/slab.h>
  15 #include <linux/spinlock.h>
  16 #include <uapi/linux/ntsync.h>
  17
  18 #define NTSYNC_NAME     "ntsync"
  19
  20 enum ntsync_type {
  21         NTSYNC_TYPE_SEM,
  22 };
  23
  24 /*
  25  * Individual synchronization primitives are represented by
  26  * struct ntsync_obj, and each primitive is backed by a file.
  27  *
  28  * The whole namespace is represented by a struct ntsync_device also
  29  * backed by a file.
  30  *
  31  * Both rely on struct file for reference counting. Individual
  32  * ntsync_obj objects take a reference to the device when created.
  33  */
  34
  35 struct ntsync_obj {
  36         spinlock_t lock;
  37
  38         enum ntsync_type type;
  39
  40         struct file *file;
  41         struct ntsync_device *dev;
  42
  43         /* The following fields are protected by the object lock. */
  44         union {
  45                 struct {
  46                         __u32 count;
  47                         __u32 max;
  48                 } sem;
  49         } u;
  50 };
  51
  52 struct ntsync_device {
  53         struct file *file;
  54 };
  55
  56 /*
  57  * Actually change the semaphore state, returning -EOVERFLOW if it is made
  58  * invalid.
  59  */
  60 static int post_sem_state(struct ntsync_obj *sem, __u32 count)
  61 {
  62         __u32 sum;
  63
  64         lockdep_assert_held(&sem->lock);
  65
  66         if (check_add_overflow(sem->u.sem.count, count, &sum) ||
  67             sum > sem->u.sem.max)
  68                 return -EOVERFLOW;
  69
  70         sem->u.sem.count = sum;
  71         return 0;
  72 }
  73
  74 static int ntsync_sem_post(struct ntsync_obj *sem, void __user *argp)
  75 {
  76         __u32 __user *user_args = argp;
  77         __u32 prev_count;
  78         __u32 args;
  79         int ret;
  80
  81         if (copy_from_user(&args, argp, sizeof(args)))
  82                 return -EFAULT;
  83
  84         if (sem->type != NTSYNC_TYPE_SEM)
  85                 return -EINVAL;
  86
  87         spin_lock(&sem->lock);
  88
  89         prev_count = sem->u.sem.count;
  90         ret = post_sem_state(sem, args);
  91
  92         spin_unlock(&sem->lock);
  93
  94         if (!ret && put_user(prev_count, user_args))
  95                 ret = -EFAULT;
  96
  97         return ret;
  98 }
  99
 100 static int ntsync_obj_release(struct inode *inode, struct file *file)
 101 {
 102         struct ntsync_obj *obj = file->private_data;
 103
 104         fput(obj->dev->file);
 105         kfree(obj);
 106
 107         return 0;
 108 }
 109
 110 static long ntsync_obj_ioctl(struct file *file, unsigned int cmd,
 111                              unsigned long parm)
 112 {
 113         struct ntsync_obj *obj = file->private_data;
 114         void __user *argp = (void __user *)parm;
 115
 116         switch (cmd) {
 117         case NTSYNC_IOC_SEM_POST:
 118                 return ntsync_sem_post(obj, argp);
 119         default:
 120                 return -ENOIOCTLCMD;
 121         }
 122 }
 123
 124 static const struct file_operations ntsync_obj_fops = {
 125         .owner          = THIS_MODULE,
 126         .release        = ntsync_obj_release,
 127         .unlocked_ioctl = ntsync_obj_ioctl,
 128         .compat_ioctl   = compat_ptr_ioctl,
 129 };
 130
 131 static struct ntsync_obj *ntsync_alloc_obj(struct ntsync_device *dev,
 132                                            enum ntsync_type type)
 133 {
 134         struct ntsync_obj *obj;
 135
 136         obj = kzalloc(sizeof(*obj), GFP_KERNEL);
 137         if (!obj)
 138                 return NULL;
 139         obj->type = type;
 140         obj->dev = dev;
 141         get_file(dev->file);
 142         spin_lock_init(&obj->lock);
 143
 144         return obj;
 145 }
 146
 147 static int ntsync_obj_get_fd(struct ntsync_obj *obj)
 148 {
 149         struct file *file;
 150         int fd;
 151
 152         fd = get_unused_fd_flags(O_CLOEXEC);
 153         if (fd < 0)
 154                 return fd;
 155         file = anon_inode_getfile("ntsync", &ntsync_obj_fops, obj, O_RDWR);
 156         if (IS_ERR(file)) {
 157                 put_unused_fd(fd);
 158                 return PTR_ERR(file);
 159         }
 160         obj->file = file;
 161         fd_install(fd, file);
 162
 163         return fd;
 164 }
 165
 166 static int ntsync_create_sem(struct ntsync_device *dev, void __user *argp)
 167 {
 168         struct ntsync_sem_args __user *user_args = argp;
 169         struct ntsync_sem_args args;
 170         struct ntsync_obj *sem;
 171         int fd;
 172
 173         if (copy_from_user(&args, argp, sizeof(args)))
 174                 return -EFAULT;
 175
 176         if (args.count > args.max)
 177                 return -EINVAL;
 178
 179         sem = ntsync_alloc_obj(dev, NTSYNC_TYPE_SEM);
 180         if (!sem)
 181                 return -ENOMEM;
 182         sem->u.sem.count = args.count;
 183         sem->u.sem.max = args.max;
 184         fd = ntsync_obj_get_fd(sem);
 185         if (fd < 0) {
 186                 kfree(sem);
 187                 return fd;
 188         }
 189
 190         return put_user(fd, &user_args->sem);
 191 }
 192
 193 static int ntsync_char_open(struct inode *inode, struct file *file)
 194 {
 195         struct ntsync_device *dev;
 196
 197         dev = kzalloc(sizeof(*dev), GFP_KERNEL);
 198         if (!dev)
 199                 return -ENOMEM;
 200
 201         file->private_data = dev;
 202         dev->file = file;
 203         return nonseekable_open(inode, file);
 204 }
 205
 206 static int ntsync_char_release(struct inode *inode, struct file *file)
 207 {
 208         struct ntsync_device *dev = file->private_data;
 209
 210         kfree(dev);
 211
 212         return 0;
 213 }
 214
 215 static long ntsync_char_ioctl(struct file *file, unsigned int cmd,
 216                               unsigned long parm)
 217 {
 218         struct ntsync_device *dev = file->private_data;
 219         void __user *argp = (void __user *)parm;
 220
 221         switch (cmd) {
 222         case NTSYNC_IOC_CREATE_SEM:
 223                 return ntsync_create_sem(dev, argp);
 224         default:
 225                 return -ENOIOCTLCMD;
 226         }
 227 }
 228
 229 static const struct file_operations ntsync_fops = {
 230         .owner          = THIS_MODULE,
 231         .open           = ntsync_char_open,
 232         .release        = ntsync_char_release,
 233         .unlocked_ioctl = ntsync_char_ioctl,
 234         .compat_ioctl   = compat_ptr_ioctl,
 235 };
 236
 237 static struct miscdevice ntsync_misc = {
 238         .minor          = MISC_DYNAMIC_MINOR,
 239         .name           = NTSYNC_NAME,
 240         .fops           = &ntsync_fops,
 241 };
 242
 243 module_misc_device(ntsync_misc);
 244
 245 MODULE_AUTHOR("Elizabeth Figura <zfigura@codeweavers.com>");
 246 MODULE_DESCRIPTION("Kernel driver for NT synchronization primitives");
 247 MODULE_LICENSE("GPL");