xref: /kernel/linux/linux-5.10/drivers/char/raw.c (revision 8c2ecf20) 
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
30struct raw_device_data {
31	dev_t binding;
32	struct block_device *bdev;
33	int inuse;
34};
35
36static struct class *raw_class;
37static struct raw_device_data *raw_devices;
38static DEFINE_MUTEX(raw_mutex);
39static const struct file_operations raw_ctl_fops; /* forward declaration */
40
41static int max_raw_minors = CONFIG_MAX_RAW_DEVS;
42
43module_param(max_raw_minors, int, 0);
44MODULE_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 */
56static 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
99out1:
100	blkdev_put(bdev, filp->f_mode | FMODE_EXCL);
101out:
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 */
110static 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 */
129static long
130raw_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
136static 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
189static 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 */
201static 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
236struct raw32_config_request {
237	compat_int_t	raw_minor;
238	compat_u64	block_major;
239	compat_u64	block_minor;
240};
241
242static 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
278static 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
289static 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
299static struct cdev raw_cdev;
300
301static char *raw_devnode(struct device *dev, umode_t *mode)
302{
303	return kasprintf(GFP_KERNEL, "raw/%s", dev_name(dev));
304}
305
306static 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
345error_region:
346	unregister_chrdev_region(dev, max_raw_minors);
347error:
348	vfree(raw_devices);
349	return ret;
350}
351
352static 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
360module_init(raw_init);
361module_exit(raw_exit);
362MODULE_LICENSE("GPL");
363