1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  * file.c - operations for regular (text) files.
4  *
5  * Based on sysfs:
6  * 	sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
7  *
8  * configfs Copyright (C) 2005 Oracle.  All rights reserved.
9  */
10 
11 #include <linux/fs.h>
12 #include <linux/module.h>
13 #include <linux/slab.h>
14 #include <linux/mutex.h>
15 #include <linux/vmalloc.h>
16 #include <linux/uaccess.h>
17 #include <linux/uio.h>
18 #include <linux/configfs.h>
19 #include "configfs_internal.h"
20 
21 /*
22  * A simple attribute can only be 4096 characters.  Why 4k?  Because the
23  * original code limited it to PAGE_SIZE.  That's a bad idea, though,
24  * because an attribute of 16k on ia64 won't work on x86.  So we limit to
25  * 4k, our minimum common page size.
26  */
27 #define SIMPLE_ATTR_SIZE 4096
28 
29 struct configfs_buffer {
30 	size_t			count;
31 	loff_t			pos;
32 	char			* page;
33 	struct configfs_item_operations	* ops;
34 	struct mutex		mutex;
35 	int			needs_read_fill;
36 	bool			read_in_progress;
37 	bool			write_in_progress;
38 	char			*bin_buffer;
39 	int			bin_buffer_size;
40 	int			cb_max_size;
41 	struct config_item	*item;
42 	struct module		*owner;
43 	union {
44 		struct configfs_attribute	*attr;
45 		struct configfs_bin_attribute	*bin_attr;
46 	};
47 };
48 
to_frag(struct file * file)49 static inline struct configfs_fragment *to_frag(struct file *file)
50 {
51 	struct configfs_dirent *sd = file->f_path.dentry->d_fsdata;
52 
53 	return sd->s_frag;
54 }
55 
fill_read_buffer(struct file * file,struct configfs_buffer * buffer)56 static int fill_read_buffer(struct file *file, struct configfs_buffer *buffer)
57 {
58 	struct configfs_fragment *frag = to_frag(file);
59 	ssize_t count = -ENOENT;
60 
61 	if (!buffer->page)
62 		buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
63 	if (!buffer->page)
64 		return -ENOMEM;
65 
66 	down_read(&frag->frag_sem);
67 	if (!frag->frag_dead)
68 		count = buffer->attr->show(buffer->item, buffer->page);
69 	up_read(&frag->frag_sem);
70 
71 	if (count < 0)
72 		return count;
73 	if (WARN_ON_ONCE(count > (ssize_t)SIMPLE_ATTR_SIZE))
74 		return -EIO;
75 	buffer->needs_read_fill = 0;
76 	buffer->count = count;
77 	return 0;
78 }
79 
configfs_read_iter(struct kiocb * iocb,struct iov_iter * to)80 static ssize_t configfs_read_iter(struct kiocb *iocb, struct iov_iter *to)
81 {
82 	struct file *file = iocb->ki_filp;
83 	struct configfs_buffer *buffer = file->private_data;
84 	ssize_t retval = 0;
85 
86 	mutex_lock(&buffer->mutex);
87 	if (buffer->needs_read_fill) {
88 		retval = fill_read_buffer(file, buffer);
89 		if (retval)
90 			goto out;
91 	}
92 	pr_debug("%s: count = %zd, pos = %lld, buf = %s\n",
93 		 __func__, iov_iter_count(to), iocb->ki_pos, buffer->page);
94 	if (iocb->ki_pos >= buffer->count)
95 		goto out;
96 	retval = copy_to_iter(buffer->page + iocb->ki_pos,
97 			      buffer->count - iocb->ki_pos, to);
98 	iocb->ki_pos += retval;
99 	if (retval == 0)
100 		retval = -EFAULT;
101 out:
102 	mutex_unlock(&buffer->mutex);
103 	return retval;
104 }
105 
configfs_bin_read_iter(struct kiocb * iocb,struct iov_iter * to)106 static ssize_t configfs_bin_read_iter(struct kiocb *iocb, struct iov_iter *to)
107 {
108 	struct file *file = iocb->ki_filp;
109 	struct configfs_fragment *frag = to_frag(file);
110 	struct configfs_buffer *buffer = file->private_data;
111 	ssize_t retval = 0;
112 	ssize_t len;
113 
114 	mutex_lock(&buffer->mutex);
115 
116 	/* we don't support switching read/write modes */
117 	if (buffer->write_in_progress) {
118 		retval = -ETXTBSY;
119 		goto out;
120 	}
121 	buffer->read_in_progress = true;
122 
123 	if (buffer->needs_read_fill) {
124 		/* perform first read with buf == NULL to get extent */
125 		down_read(&frag->frag_sem);
126 		if (!frag->frag_dead)
127 			len = buffer->bin_attr->read(buffer->item, NULL, 0);
128 		else
129 			len = -ENOENT;
130 		up_read(&frag->frag_sem);
131 		if (len <= 0) {
132 			retval = len;
133 			goto out;
134 		}
135 
136 		/* do not exceed the maximum value */
137 		if (buffer->cb_max_size && len > buffer->cb_max_size) {
138 			retval = -EFBIG;
139 			goto out;
140 		}
141 
142 		buffer->bin_buffer = vmalloc(len);
143 		if (buffer->bin_buffer == NULL) {
144 			retval = -ENOMEM;
145 			goto out;
146 		}
147 		buffer->bin_buffer_size = len;
148 
149 		/* perform second read to fill buffer */
150 		down_read(&frag->frag_sem);
151 		if (!frag->frag_dead)
152 			len = buffer->bin_attr->read(buffer->item,
153 						     buffer->bin_buffer, len);
154 		else
155 			len = -ENOENT;
156 		up_read(&frag->frag_sem);
157 		if (len < 0) {
158 			retval = len;
159 			vfree(buffer->bin_buffer);
160 			buffer->bin_buffer_size = 0;
161 			buffer->bin_buffer = NULL;
162 			goto out;
163 		}
164 
165 		buffer->needs_read_fill = 0;
166 	}
167 
168 	if (iocb->ki_pos >= buffer->bin_buffer_size)
169 		goto out;
170 	retval = copy_to_iter(buffer->bin_buffer + iocb->ki_pos,
171 			      buffer->bin_buffer_size - iocb->ki_pos, to);
172 	iocb->ki_pos += retval;
173 	if (retval == 0)
174 		retval = -EFAULT;
175 out:
176 	mutex_unlock(&buffer->mutex);
177 	return retval;
178 }
179 
180 /* Fill @buffer with data coming from @from. */
fill_write_buffer(struct configfs_buffer * buffer,struct iov_iter * from)181 static int fill_write_buffer(struct configfs_buffer *buffer,
182 			     struct iov_iter *from)
183 {
184 	int copied;
185 
186 	if (!buffer->page)
187 		buffer->page = (char *)__get_free_pages(GFP_KERNEL, 0);
188 	if (!buffer->page)
189 		return -ENOMEM;
190 
191 	copied = copy_from_iter(buffer->page, SIMPLE_ATTR_SIZE - 1, from);
192 	buffer->needs_read_fill = 1;
193 	/* if buf is assumed to contain a string, terminate it by \0,
194 	 * so e.g. sscanf() can scan the string easily */
195 	buffer->page[copied] = 0;
196 	return copied ? : -EFAULT;
197 }
198 
199 static int
flush_write_buffer(struct file * file,struct configfs_buffer * buffer,size_t count)200 flush_write_buffer(struct file *file, struct configfs_buffer *buffer, size_t count)
201 {
202 	struct configfs_fragment *frag = to_frag(file);
203 	int res = -ENOENT;
204 
205 	down_read(&frag->frag_sem);
206 	if (!frag->frag_dead)
207 		res = buffer->attr->store(buffer->item, buffer->page, count);
208 	up_read(&frag->frag_sem);
209 	return res;
210 }
211 
212 
213 /*
214  * There is no easy way for us to know if userspace is only doing a partial
215  * write, so we don't support them. We expect the entire buffer to come on the
216  * first write.
217  * Hint: if you're writing a value, first read the file, modify only the value
218  * you're changing, then write entire buffer back.
219  */
configfs_write_iter(struct kiocb * iocb,struct iov_iter * from)220 static ssize_t configfs_write_iter(struct kiocb *iocb, struct iov_iter *from)
221 {
222 	struct file *file = iocb->ki_filp;
223 	struct configfs_buffer *buffer = file->private_data;
224 	int len;
225 
226 	mutex_lock(&buffer->mutex);
227 	len = fill_write_buffer(buffer, from);
228 	if (len > 0)
229 		len = flush_write_buffer(file, buffer, len);
230 	if (len > 0)
231 		iocb->ki_pos += len;
232 	mutex_unlock(&buffer->mutex);
233 	return len;
234 }
235 
configfs_bin_write_iter(struct kiocb * iocb,struct iov_iter * from)236 static ssize_t configfs_bin_write_iter(struct kiocb *iocb,
237 				       struct iov_iter *from)
238 {
239 	struct file *file = iocb->ki_filp;
240 	struct configfs_buffer *buffer = file->private_data;
241 	void *tbuf = NULL;
242 	size_t end_offset;
243 	ssize_t len;
244 
245 	mutex_lock(&buffer->mutex);
246 
247 	/* we don't support switching read/write modes */
248 	if (buffer->read_in_progress) {
249 		len = -ETXTBSY;
250 		goto out;
251 	}
252 	buffer->write_in_progress = true;
253 
254 	/* buffer grows? */
255 	end_offset = iocb->ki_pos + iov_iter_count(from);
256 	if (end_offset > buffer->bin_buffer_size) {
257 		if (buffer->cb_max_size && end_offset > buffer->cb_max_size) {
258 			len = -EFBIG;
259 			goto out;
260 		}
261 
262 		tbuf = vmalloc(end_offset);
263 		if (tbuf == NULL) {
264 			len = -ENOMEM;
265 			goto out;
266 		}
267 
268 		/* copy old contents */
269 		if (buffer->bin_buffer) {
270 			memcpy(tbuf, buffer->bin_buffer,
271 				buffer->bin_buffer_size);
272 			vfree(buffer->bin_buffer);
273 		}
274 
275 		/* clear the new area */
276 		memset(tbuf + buffer->bin_buffer_size, 0,
277 			end_offset - buffer->bin_buffer_size);
278 		buffer->bin_buffer = tbuf;
279 		buffer->bin_buffer_size = end_offset;
280 	}
281 
282 	len = copy_from_iter(buffer->bin_buffer + iocb->ki_pos,
283 			     buffer->bin_buffer_size - iocb->ki_pos, from);
284 	iocb->ki_pos += len;
285 out:
286 	mutex_unlock(&buffer->mutex);
287 	return len ? : -EFAULT;
288 }
289 
__configfs_open_file(struct inode * inode,struct file * file,int type)290 static int __configfs_open_file(struct inode *inode, struct file *file, int type)
291 {
292 	struct dentry *dentry = file->f_path.dentry;
293 	struct configfs_fragment *frag = to_frag(file);
294 	struct configfs_attribute *attr;
295 	struct configfs_buffer *buffer;
296 	int error;
297 
298 	error = -ENOMEM;
299 	buffer = kzalloc(sizeof(struct configfs_buffer), GFP_KERNEL);
300 	if (!buffer)
301 		goto out;
302 
303 	error = -ENOENT;
304 	down_read(&frag->frag_sem);
305 	if (unlikely(frag->frag_dead))
306 		goto out_free_buffer;
307 
308 	error = -EINVAL;
309 	buffer->item = to_item(dentry->d_parent);
310 	if (!buffer->item)
311 		goto out_free_buffer;
312 
313 	attr = to_attr(dentry);
314 	if (!attr)
315 		goto out_free_buffer;
316 
317 	if (type & CONFIGFS_ITEM_BIN_ATTR) {
318 		buffer->bin_attr = to_bin_attr(dentry);
319 		buffer->cb_max_size = buffer->bin_attr->cb_max_size;
320 	} else {
321 		buffer->attr = attr;
322 	}
323 
324 	buffer->owner = attr->ca_owner;
325 	/* Grab the module reference for this attribute if we have one */
326 	error = -ENODEV;
327 	if (!try_module_get(buffer->owner))
328 		goto out_free_buffer;
329 
330 	error = -EACCES;
331 	if (!buffer->item->ci_type)
332 		goto out_put_module;
333 
334 	buffer->ops = buffer->item->ci_type->ct_item_ops;
335 
336 	/* File needs write support.
337 	 * The inode's perms must say it's ok,
338 	 * and we must have a store method.
339 	 */
340 	if (file->f_mode & FMODE_WRITE) {
341 		if (!(inode->i_mode & S_IWUGO))
342 			goto out_put_module;
343 		if ((type & CONFIGFS_ITEM_ATTR) && !attr->store)
344 			goto out_put_module;
345 		if ((type & CONFIGFS_ITEM_BIN_ATTR) && !buffer->bin_attr->write)
346 			goto out_put_module;
347 	}
348 
349 	/* File needs read support.
350 	 * The inode's perms must say it's ok, and we there
351 	 * must be a show method for it.
352 	 */
353 	if (file->f_mode & FMODE_READ) {
354 		if (!(inode->i_mode & S_IRUGO))
355 			goto out_put_module;
356 		if ((type & CONFIGFS_ITEM_ATTR) && !attr->show)
357 			goto out_put_module;
358 		if ((type & CONFIGFS_ITEM_BIN_ATTR) && !buffer->bin_attr->read)
359 			goto out_put_module;
360 	}
361 
362 	mutex_init(&buffer->mutex);
363 	buffer->needs_read_fill = 1;
364 	buffer->read_in_progress = false;
365 	buffer->write_in_progress = false;
366 	file->private_data = buffer;
367 	up_read(&frag->frag_sem);
368 	return 0;
369 
370 out_put_module:
371 	module_put(buffer->owner);
372 out_free_buffer:
373 	up_read(&frag->frag_sem);
374 	kfree(buffer);
375 out:
376 	return error;
377 }
378 
configfs_release(struct inode * inode,struct file * filp)379 static int configfs_release(struct inode *inode, struct file *filp)
380 {
381 	struct configfs_buffer *buffer = filp->private_data;
382 
383 	module_put(buffer->owner);
384 	if (buffer->page)
385 		free_page((unsigned long)buffer->page);
386 	mutex_destroy(&buffer->mutex);
387 	kfree(buffer);
388 	return 0;
389 }
390 
configfs_open_file(struct inode * inode,struct file * filp)391 static int configfs_open_file(struct inode *inode, struct file *filp)
392 {
393 	return __configfs_open_file(inode, filp, CONFIGFS_ITEM_ATTR);
394 }
395 
configfs_open_bin_file(struct inode * inode,struct file * filp)396 static int configfs_open_bin_file(struct inode *inode, struct file *filp)
397 {
398 	return __configfs_open_file(inode, filp, CONFIGFS_ITEM_BIN_ATTR);
399 }
400 
configfs_release_bin_file(struct inode * inode,struct file * file)401 static int configfs_release_bin_file(struct inode *inode, struct file *file)
402 {
403 	struct configfs_buffer *buffer = file->private_data;
404 
405 	if (buffer->write_in_progress) {
406 		struct configfs_fragment *frag = to_frag(file);
407 
408 		down_read(&frag->frag_sem);
409 		if (!frag->frag_dead) {
410 			/* result of ->release() is ignored */
411 			buffer->bin_attr->write(buffer->item,
412 					buffer->bin_buffer,
413 					buffer->bin_buffer_size);
414 		}
415 		up_read(&frag->frag_sem);
416 	}
417 
418 	vfree(buffer->bin_buffer);
419 
420 	configfs_release(inode, file);
421 	return 0;
422 }
423 
424 
425 const struct file_operations configfs_file_operations = {
426 	.read_iter	= configfs_read_iter,
427 	.write_iter	= configfs_write_iter,
428 	.llseek		= generic_file_llseek,
429 	.open		= configfs_open_file,
430 	.release	= configfs_release,
431 };
432 
433 const struct file_operations configfs_bin_file_operations = {
434 	.read_iter	= configfs_bin_read_iter,
435 	.write_iter	= configfs_bin_write_iter,
436 	.llseek		= NULL,		/* bin file is not seekable */
437 	.open		= configfs_open_bin_file,
438 	.release	= configfs_release_bin_file,
439 };
440 
441 /**
442  *	configfs_create_file - create an attribute file for an item.
443  *	@item:	item we're creating for.
444  *	@attr:	atrribute descriptor.
445  */
446 
configfs_create_file(struct config_item * item,const struct configfs_attribute * attr)447 int configfs_create_file(struct config_item * item, const struct configfs_attribute * attr)
448 {
449 	struct dentry *dir = item->ci_dentry;
450 	struct configfs_dirent *parent_sd = dir->d_fsdata;
451 	umode_t mode = (attr->ca_mode & S_IALLUGO) | S_IFREG;
452 	int error = 0;
453 
454 	inode_lock_nested(d_inode(dir), I_MUTEX_NORMAL);
455 	error = configfs_make_dirent(parent_sd, NULL, (void *) attr, mode,
456 				     CONFIGFS_ITEM_ATTR, parent_sd->s_frag);
457 	inode_unlock(d_inode(dir));
458 
459 	return error;
460 }
461 
462 /**
463  *	configfs_create_bin_file - create a binary attribute file for an item.
464  *	@item:	item we're creating for.
465  *	@bin_attr: atrribute descriptor.
466  */
467 
configfs_create_bin_file(struct config_item * item,const struct configfs_bin_attribute * bin_attr)468 int configfs_create_bin_file(struct config_item *item,
469 		const struct configfs_bin_attribute *bin_attr)
470 {
471 	struct dentry *dir = item->ci_dentry;
472 	struct configfs_dirent *parent_sd = dir->d_fsdata;
473 	umode_t mode = (bin_attr->cb_attr.ca_mode & S_IALLUGO) | S_IFREG;
474 	int error = 0;
475 
476 	inode_lock_nested(dir->d_inode, I_MUTEX_NORMAL);
477 	error = configfs_make_dirent(parent_sd, NULL, (void *) bin_attr, mode,
478 				     CONFIGFS_ITEM_BIN_ATTR, parent_sd->s_frag);
479 	inode_unlock(dir->d_inode);
480 
481 	return error;
482 }
483