drivers/char/raw.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * linux/drivers/char/raw.c
   4  *
   5  * Front-end raw character devices.  These can be bound to any block
   6  * devices to provide genuine Unix raw character device semantics.
   7  *
   8  * We reserve minor number 0 for a control interface.  ioctl()s on this
   9  * device are used to bind the other minor numbers to block devices.
  10  */
  11
  12 #include <linux/init.h>
  13 #include <linux/fs.h>
  14 #include <linux/major.h>
  15 #include <linux/blkdev.h>
  16 #include <linux/backing-dev.h>
  17 #include <linux/module.h>
  18 #include <linux/raw.h>
  19 #include <linux/capability.h>
  20 #include <linux/uio.h>
  21 #include <linux/cdev.h>
  22 #include <linux/device.h>
  23 #include <linux/mutex.h>
  24 #include <linux/gfp.h>
  25 #include <linux/compat.h>
  26 #include <linux/vmalloc.h>
  27
  28 #include <linux/uaccess.h>
  29
  30 struct raw_device_data {
  31         dev_t binding;
  32         struct block_device *bdev;
  33         int inuse;
  34 };
  35
  36 static struct class *raw_class;
  37 static struct raw_device_data *raw_devices;
  38 static DEFINE_MUTEX(raw_mutex);
  39 static const struct file_operations raw_ctl_fops; /* forward declaration */
  40
  41 static int max_raw_minors = CONFIG_MAX_RAW_DEVS;
  42
  43 module_param(max_raw_minors, int, 0);
  44 MODULE_PARM_DESC(max_raw_minors, "Maximum number of raw devices (1-65536)");
  45
  46 /*
  47  * Open/close code for raw IO.
  48  *
  49  * We just rewrite the i_mapping for the /dev/raw/rawN file descriptor to
  50  * point at the blockdev's address_space and set the file handle to use
  51  * O_DIRECT.
  52  *
  53  * Set the device's soft blocksize to the minimum possible.  This gives the
  54  * finest possible alignment and has no adverse impact on performance.
  55  */
  56 static int raw_open(struct inode *inode, struct file *filp)
  57 {
  58         const int minor = iminor(inode);
  59         struct block_device *bdev;
  60         int err;
  61
  62         if (minor == 0) {       /* It is the control device */
  63                 filp->f_op = &raw_ctl_fops;
  64                 return 0;
  65         }
  66
  67         pr_warn_ratelimited(
  68                 "process %s (pid %d) is using the deprecated raw device\n"
  69                 "support will be removed in Linux 5.14.\n",
  70                 current->comm, current->pid);
  71
  72         mutex_lock(&raw_mutex);
  73
  74         /*
  75          * All we need to do on open is check that the device is bound.
  76          */
  77         err = -ENODEV;
  78         if (!raw_devices[minor].binding)
  79                 goto out;
  80         bdev = blkdev_get_by_dev(raw_devices[minor].binding,
  81                                  filp->f_mode | FMODE_EXCL, raw_open);
  82         if (IS_ERR(bdev)) {
  83                 err = PTR_ERR(bdev);
  84                 goto out;
  85         }
  86         err = set_blocksize(bdev, bdev_logical_block_size(bdev));
  87         if (err)
  88                 goto out1;
  89         filp->f_flags |= O_DIRECT;
  90         filp->f_mapping = bdev->bd_inode->i_mapping;
  91         if (++raw_devices[minor].inuse == 1)
  92                 file_inode(filp)->i_mapping =
  93                         bdev->bd_inode->i_mapping;
  94         filp->private_data = bdev;
  95         raw_devices[minor].bdev = bdev;
  96         mutex_unlock(&raw_mutex);
  97         return 0;
  98
  99 out1:
 100         blkdev_put(bdev, filp->f_mode | FMODE_EXCL);
 101 out:
 102         mutex_unlock(&raw_mutex);
 103         return err;
 104 }
 105
 106 /*
 107  * When the final fd which refers to this character-special node is closed, we
 108  * make its ->mapping point back at its own i_data.
 109  */
 110 static int raw_release(struct inode *inode, struct file *filp)
 111 {
 112         const int minor= iminor(inode);
 113         struct block_device *bdev;
 114
 115         mutex_lock(&raw_mutex);
 116         bdev = raw_devices[minor].bdev;
 117         if (--raw_devices[minor].inuse == 0)
 118                 /* Here  inode->i_mapping == bdev->bd_inode->i_mapping  */
 119                 inode->i_mapping = &inode->i_data;
 120         mutex_unlock(&raw_mutex);
 121
 122         blkdev_put(bdev, filp->f_mode | FMODE_EXCL);
 123         return 0;
 124 }
 125
 126 /*
 127  * Forward ioctls to the underlying block device.
 128  */
 129 static long
 130 raw_ioctl(struct file *filp, unsigned int command, unsigned long arg)
 131 {
 132         struct block_device *bdev = filp->private_data;
 133         return blkdev_ioctl(bdev, 0, command, arg);
 134 }
 135
 136 static int bind_set(int number, u64 major, u64 minor)
 137 {
 138         dev_t dev = MKDEV(major, minor);
 139         dev_t raw = MKDEV(RAW_MAJOR, number);
 140         struct raw_device_data *rawdev;
 141         int err = 0;
 142
 143         if (number <= 0 || number >= max_raw_minors)
 144                 return -EINVAL;
 145
 146         if (MAJOR(dev) != major || MINOR(dev) != minor)
 147                 return -EINVAL;
 148
 149         rawdev = &raw_devices[number];
 150
 151         /*
 152          * This is like making block devices, so demand the
 153          * same capability
 154          */
 155         if (!capable(CAP_SYS_ADMIN))
 156                 return -EPERM;
 157
 158         /*
 159          * For now, we don't need to check that the underlying
 160          * block device is present or not: we can do that when
 161          * the raw device is opened.  Just check that the
 162          * major/minor numbers make sense.
 163          */
 164
 165         if (MAJOR(dev) == 0 && dev != 0)
 166                 return -EINVAL;
 167
 168         mutex_lock(&raw_mutex);
 169         if (rawdev->inuse) {
 170                 mutex_unlock(&raw_mutex);
 171                 return -EBUSY;
 172         }
 173         if (rawdev->binding)
 174                 module_put(THIS_MODULE);
 175
 176         rawdev->binding = dev;
 177         if (!dev) {
 178                 /* unbind */
 179                 device_destroy(raw_class, raw);
 180         } else {
 181                 __module_get(THIS_MODULE);
 182                 device_destroy(raw_class, raw);
 183                 device_create(raw_class, NULL, raw, NULL, "raw%d", number);
 184         }
 185         mutex_unlock(&raw_mutex);
 186         return err;
 187 }
 188
 189 static int bind_get(int number, dev_t *dev)
 190 {
 191         if (number <= 0 || number >= max_raw_minors)
 192                 return -EINVAL;
 193         *dev = raw_devices[number].binding;
 194         return 0;
 195 }
 196
 197 /*
 198  * Deal with ioctls against the raw-device control interface, to bind
 199  * and unbind other raw devices.
 200  */
 201 static long raw_ctl_ioctl(struct file *filp, unsigned int command,
 202                           unsigned long arg)
 203 {
 204         struct raw_config_request rq;
 205         dev_t dev;
 206         int err;
 207
 208         switch (command) {
 209         case RAW_SETBIND:
 210                 if (copy_from_user(&rq, (void __user *) arg, sizeof(rq)))
 211                         return -EFAULT;
 212
 213                 return bind_set(rq.raw_minor, rq.block_major, rq.block_minor);
 214
 215         case RAW_GETBIND:
 216                 if (copy_from_user(&rq, (void __user *) arg, sizeof(rq)))
 217                         return -EFAULT;
 218
 219                 err = bind_get(rq.raw_minor, &dev);
 220                 if (err)
 221                         return err;
 222
 223                 rq.block_major = MAJOR(dev);
 224                 rq.block_minor = MINOR(dev);
 225
 226                 if (copy_to_user((void __user *)arg, &rq, sizeof(rq)))
 227                         return -EFAULT;
 228
 229                 return 0;
 230         }
 231
 232         return -EINVAL;
 233 }
 234
 235 #ifdef CONFIG_COMPAT
 236 struct raw32_config_request {
 237         compat_int_t    raw_minor;
 238         compat_u64      block_major;
 239         compat_u64      block_minor;
 240 };
 241
 242 static long raw_ctl_compat_ioctl(struct file *file, unsigned int cmd,
 243                                 unsigned long arg)
 244 {
 245         struct raw32_config_request __user *user_req = compat_ptr(arg);
 246         struct raw32_config_request rq;
 247         dev_t dev;
 248         int err = 0;
 249
 250         switch (cmd) {
 251         case RAW_SETBIND:
 252                 if (copy_from_user(&rq, user_req, sizeof(rq)))
 253                         return -EFAULT;
 254
 255                 return bind_set(rq.raw_minor, rq.block_major, rq.block_minor);
 256
 257         case RAW_GETBIND:
 258                 if (copy_from_user(&rq, user_req, sizeof(rq)))
 259                         return -EFAULT;
 260
 261                 err = bind_get(rq.raw_minor, &dev);
 262                 if (err)
 263                         return err;
 264
 265                 rq.block_major = MAJOR(dev);
 266                 rq.block_minor = MINOR(dev);
 267
 268                 if (copy_to_user(user_req, &rq, sizeof(rq)))
 269                         return -EFAULT;
 270
 271                 return 0;
 272         }
 273
 274         return -EINVAL;
 275 }
 276 #endif
 277
 278 static const struct file_operations raw_fops = {
 279         .read_iter      = blkdev_read_iter,
 280         .write_iter     = blkdev_write_iter,
 281         .fsync          = blkdev_fsync,
 282         .open           = raw_open,
 283         .release        = raw_release,
 284         .unlocked_ioctl = raw_ioctl,
 285         .llseek         = default_llseek,
 286         .owner          = THIS_MODULE,
 287 };
 288
 289 static const struct file_operations raw_ctl_fops = {
 290         .unlocked_ioctl = raw_ctl_ioctl,
 291 #ifdef CONFIG_COMPAT
 292         .compat_ioctl   = raw_ctl_compat_ioctl,
 293 #endif
 294         .open           = raw_open,
 295         .owner          = THIS_MODULE,
 296         .llseek         = noop_llseek,
 297 };
 298
 299 static struct cdev raw_cdev;
 300
 301 static char *raw_devnode(struct device *dev, umode_t *mode)
 302 {
 303         return kasprintf(GFP_KERNEL, "raw/%s", dev_name(dev));
 304 }
 305
 306 static int __init raw_init(void)
 307 {
 308         dev_t dev = MKDEV(RAW_MAJOR, 0);
 309         int ret;
 310
 311         if (max_raw_minors < 1 || max_raw_minors > 65536) {
 312                 pr_warn("raw: invalid max_raw_minors (must be between 1 and 65536), using %d\n",
 313                         CONFIG_MAX_RAW_DEVS);
 314                 max_raw_minors = CONFIG_MAX_RAW_DEVS;
 315         }
 316
 317         raw_devices = vzalloc(array_size(max_raw_minors,
 318                                          sizeof(struct raw_device_data)));
 319         if (!raw_devices) {
 320                 printk(KERN_ERR "Not enough memory for raw device structures\n");
 321                 ret = -ENOMEM;
 322                 goto error;
 323         }
 324
 325         ret = register_chrdev_region(dev, max_raw_minors, "raw");
 326         if (ret)
 327                 goto error;
 328
 329         cdev_init(&raw_cdev, &raw_fops);
 330         ret = cdev_add(&raw_cdev, dev, max_raw_minors);
 331         if (ret)
 332                 goto error_region;
 333         raw_class = class_create(THIS_MODULE, "raw");
 334         if (IS_ERR(raw_class)) {
 335                 printk(KERN_ERR "Error creating raw class.\n");
 336                 cdev_del(&raw_cdev);
 337                 ret = PTR_ERR(raw_class);
 338                 goto error_region;
 339         }
 340         raw_class->devnode = raw_devnode;
 341         device_create(raw_class, NULL, MKDEV(RAW_MAJOR, 0), NULL, "rawctl");
 342
 343         return 0;
 344
 345 error_region:
 346         unregister_chrdev_region(dev, max_raw_minors);
 347 error:
 348         vfree(raw_devices);
 349         return ret;
 350 }
 351
 352 static void __exit raw_exit(void)
 353 {
 354         device_destroy(raw_class, MKDEV(RAW_MAJOR, 0));
 355         class_destroy(raw_class);
 356         cdev_del(&raw_cdev);
 357         unregister_chrdev_region(MKDEV(RAW_MAJOR, 0), max_raw_minors);
 358 }
 359
 360 module_init(raw_init);
 361 module_exit(raw_exit);
 362 MODULE_LICENSE("GPL");