fs/configfs/file.c

0001 // SPDX-License-Identifier: GPL-2.0-or-later
0002 /*
0003  * file.c - operations for regular (text) files.
0004  *
0005  * Based on sysfs:
0006  *  sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
0007  *
0008  * configfs Copyright (C) 2005 Oracle.  All rights reserved.
0009  */
0010
0011 #include <linux/fs.h>
0012 #include <linux/module.h>
0013 #include <linux/slab.h>
0014 #include <linux/mutex.h>
0015 #include <linux/vmalloc.h>
0016 #include <linux/uaccess.h>
0017 #include <linux/uio.h>
0018 #include <linux/configfs.h>
0019 #include "configfs_internal.h"
0020
0021 /*
0022  * A simple attribute can only be 4096 characters.  Why 4k?  Because the
0023  * original code limited it to PAGE_SIZE.  That's a bad idea, though,
0024  * because an attribute of 16k on ia64 won't work on x86.  So we limit to
0025  * 4k, our minimum common page size.
0026  */
0027 #define SIMPLE_ATTR_SIZE 4096
0028
0029 struct configfs_buffer {
0030     size_t          count;
0031     loff_t          pos;
0032     char            * page;
0033     struct configfs_item_operations * ops;
0034     struct mutex        mutex;
0035     int         needs_read_fill;
0036     bool            read_in_progress;
0037     bool            write_in_progress;
0038     char            *bin_buffer;
0039     int         bin_buffer_size;
0040     int         cb_max_size;
0041     struct config_item  *item;
0042     struct module       *owner;
0043     union {
0044         struct configfs_attribute   *attr;
0045         struct configfs_bin_attribute   *bin_attr;
0046     };
0047 };
0048
0049 static inline struct configfs_fragment *to_frag(struct file *file)
0050 {
0051     struct configfs_dirent *sd = file->f_path.dentry->d_fsdata;
0052
0053     return sd->s_frag;
0054 }
0055
0056 static int fill_read_buffer(struct file *file, struct configfs_buffer *buffer)
0057 {
0058     struct configfs_fragment *frag = to_frag(file);
0059     ssize_t count = -ENOENT;
0060
0061     if (!buffer->page)
0062         buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
0063     if (!buffer->page)
0064         return -ENOMEM;
0065
0066     down_read(&frag->frag_sem);
0067     if (!frag->frag_dead)
0068         count = buffer->attr->show(buffer->item, buffer->page);
0069     up_read(&frag->frag_sem);
0070
0071     if (count < 0)
0072         return count;
0073     if (WARN_ON_ONCE(count > (ssize_t)SIMPLE_ATTR_SIZE))
0074         return -EIO;
0075     buffer->needs_read_fill = 0;
0076     buffer->count = count;
0077     return 0;
0078 }
0079
0080 static ssize_t configfs_read_iter(struct kiocb *iocb, struct iov_iter *to)
0081 {
0082     struct file *file = iocb->ki_filp;
0083     struct configfs_buffer *buffer = file->private_data;
0084     ssize_t retval = 0;
0085
0086     mutex_lock(&buffer->mutex);
0087     if (buffer->needs_read_fill) {
0088         retval = fill_read_buffer(file, buffer);
0089         if (retval)
0090             goto out;
0091     }
0092     pr_debug("%s: count = %zd, pos = %lld, buf = %s\n",
0093          __func__, iov_iter_count(to), iocb->ki_pos, buffer->page);
0094     if (iocb->ki_pos >= buffer->count)
0095         goto out;
0096     retval = copy_to_iter(buffer->page + iocb->ki_pos,
0097                   buffer->count - iocb->ki_pos, to);
0098     iocb->ki_pos += retval;
0099     if (retval == 0)
0100         retval = -EFAULT;
0101 out:
0102     mutex_unlock(&buffer->mutex);
0103     return retval;
0104 }
0105
0106 static ssize_t configfs_bin_read_iter(struct kiocb *iocb, struct iov_iter *to)
0107 {
0108     struct file *file = iocb->ki_filp;
0109     struct configfs_fragment *frag = to_frag(file);
0110     struct configfs_buffer *buffer = file->private_data;
0111     ssize_t retval = 0;
0112     ssize_t len;
0113
0114     mutex_lock(&buffer->mutex);
0115
0116     /* we don't support switching read/write modes */
0117     if (buffer->write_in_progress) {
0118         retval = -ETXTBSY;
0119         goto out;
0120     }
0121     buffer->read_in_progress = true;
0122
0123     if (buffer->needs_read_fill) {
0124         /* perform first read with buf == NULL to get extent */
0125         down_read(&frag->frag_sem);
0126         if (!frag->frag_dead)
0127             len = buffer->bin_attr->read(buffer->item, NULL, 0);
0128         else
0129             len = -ENOENT;
0130         up_read(&frag->frag_sem);
0131         if (len <= 0) {
0132             retval = len;
0133             goto out;
0134         }
0135
0136         /* do not exceed the maximum value */
0137         if (buffer->cb_max_size && len > buffer->cb_max_size) {
0138             retval = -EFBIG;
0139             goto out;
0140         }
0141
0142         buffer->bin_buffer = vmalloc(len);
0143         if (buffer->bin_buffer == NULL) {
0144             retval = -ENOMEM;
0145             goto out;
0146         }
0147         buffer->bin_buffer_size = len;
0148
0149         /* perform second read to fill buffer */
0150         down_read(&frag->frag_sem);
0151         if (!frag->frag_dead)
0152             len = buffer->bin_attr->read(buffer->item,
0153                              buffer->bin_buffer, len);
0154         else
0155             len = -ENOENT;
0156         up_read(&frag->frag_sem);
0157         if (len < 0) {
0158             retval = len;
0159             vfree(buffer->bin_buffer);
0160             buffer->bin_buffer_size = 0;
0161             buffer->bin_buffer = NULL;
0162             goto out;
0163         }
0164
0165         buffer->needs_read_fill = 0;
0166     }
0167
0168     if (iocb->ki_pos >= buffer->bin_buffer_size)
0169         goto out;
0170     retval = copy_to_iter(buffer->bin_buffer + iocb->ki_pos,
0171                   buffer->bin_buffer_size - iocb->ki_pos, to);
0172     iocb->ki_pos += retval;
0173     if (retval == 0)
0174         retval = -EFAULT;
0175 out:
0176     mutex_unlock(&buffer->mutex);
0177     return retval;
0178 }
0179
0180 /* Fill @buffer with data coming from @from. */
0181 static int fill_write_buffer(struct configfs_buffer *buffer,
0182                  struct iov_iter *from)
0183 {
0184     int copied;
0185
0186     if (!buffer->page)
0187         buffer->page = (char *)__get_free_pages(GFP_KERNEL, 0);
0188     if (!buffer->page)
0189         return -ENOMEM;
0190
0191     copied = copy_from_iter(buffer->page, SIMPLE_ATTR_SIZE - 1, from);
0192     buffer->needs_read_fill = 1;
0193     /* if buf is assumed to contain a string, terminate it by \0,
0194      * so e.g. sscanf() can scan the string easily */
0195     buffer->page[copied] = 0;
0196     return copied ? : -EFAULT;
0197 }
0198
0199 static int
0200 flush_write_buffer(struct file *file, struct configfs_buffer *buffer, size_t count)
0201 {
0202     struct configfs_fragment *frag = to_frag(file);
0203     int res = -ENOENT;
0204
0205     down_read(&frag->frag_sem);
0206     if (!frag->frag_dead)
0207         res = buffer->attr->store(buffer->item, buffer->page, count);
0208     up_read(&frag->frag_sem);
0209     return res;
0210 }
0211
0212
0213 /*
0214  * There is no easy way for us to know if userspace is only doing a partial
0215  * write, so we don't support them. We expect the entire buffer to come on the
0216  * first write.
0217  * Hint: if you're writing a value, first read the file, modify only the value
0218  * you're changing, then write entire buffer back.
0219  */
0220 static ssize_t configfs_write_iter(struct kiocb *iocb, struct iov_iter *from)
0221 {
0222     struct file *file = iocb->ki_filp;
0223     struct configfs_buffer *buffer = file->private_data;
0224     int len;
0225
0226     mutex_lock(&buffer->mutex);
0227     len = fill_write_buffer(buffer, from);
0228     if (len > 0)
0229         len = flush_write_buffer(file, buffer, len);
0230     if (len > 0)
0231         iocb->ki_pos += len;
0232     mutex_unlock(&buffer->mutex);
0233     return len;
0234 }
0235
0236 static ssize_t configfs_bin_write_iter(struct kiocb *iocb,
0237                        struct iov_iter *from)
0238 {
0239     struct file *file = iocb->ki_filp;
0240     struct configfs_buffer *buffer = file->private_data;
0241     void *tbuf = NULL;
0242     size_t end_offset;
0243     ssize_t len;
0244
0245     mutex_lock(&buffer->mutex);
0246
0247     /* we don't support switching read/write modes */
0248     if (buffer->read_in_progress) {
0249         len = -ETXTBSY;
0250         goto out;
0251     }
0252     buffer->write_in_progress = true;
0253
0254     /* buffer grows? */
0255     end_offset = iocb->ki_pos + iov_iter_count(from);
0256     if (end_offset > buffer->bin_buffer_size) {
0257         if (buffer->cb_max_size && end_offset > buffer->cb_max_size) {
0258             len = -EFBIG;
0259             goto out;
0260         }
0261
0262         tbuf = vmalloc(end_offset);
0263         if (tbuf == NULL) {
0264             len = -ENOMEM;
0265             goto out;
0266         }
0267
0268         /* copy old contents */
0269         if (buffer->bin_buffer) {
0270             memcpy(tbuf, buffer->bin_buffer,
0271                 buffer->bin_buffer_size);
0272             vfree(buffer->bin_buffer);
0273         }
0274
0275         /* clear the new area */
0276         memset(tbuf + buffer->bin_buffer_size, 0,
0277             end_offset - buffer->bin_buffer_size);
0278         buffer->bin_buffer = tbuf;
0279         buffer->bin_buffer_size = end_offset;
0280     }
0281
0282     len = copy_from_iter(buffer->bin_buffer + iocb->ki_pos,
0283                  buffer->bin_buffer_size - iocb->ki_pos, from);
0284     iocb->ki_pos += len;
0285 out:
0286     mutex_unlock(&buffer->mutex);
0287     return len ? : -EFAULT;
0288 }
0289
0290 static int __configfs_open_file(struct inode *inode, struct file *file, int type)
0291 {
0292     struct dentry *dentry = file->f_path.dentry;
0293     struct configfs_fragment *frag = to_frag(file);
0294     struct configfs_attribute *attr;
0295     struct configfs_buffer *buffer;
0296     int error;
0297
0298     error = -ENOMEM;
0299     buffer = kzalloc(sizeof(struct configfs_buffer), GFP_KERNEL);
0300     if (!buffer)
0301         goto out;
0302
0303     error = -ENOENT;
0304     down_read(&frag->frag_sem);
0305     if (unlikely(frag->frag_dead))
0306         goto out_free_buffer;
0307
0308     error = -EINVAL;
0309     buffer->item = to_item(dentry->d_parent);
0310     if (!buffer->item)
0311         goto out_free_buffer;
0312
0313     attr = to_attr(dentry);
0314     if (!attr)
0315         goto out_free_buffer;
0316
0317     if (type & CONFIGFS_ITEM_BIN_ATTR) {
0318         buffer->bin_attr = to_bin_attr(dentry);
0319         buffer->cb_max_size = buffer->bin_attr->cb_max_size;
0320     } else {
0321         buffer->attr = attr;
0322     }
0323
0324     buffer->owner = attr->ca_owner;
0325     /* Grab the module reference for this attribute if we have one */
0326     error = -ENODEV;
0327     if (!try_module_get(buffer->owner))
0328         goto out_free_buffer;
0329
0330     error = -EACCES;
0331     if (!buffer->item->ci_type)
0332         goto out_put_module;
0333
0334     buffer->ops = buffer->item->ci_type->ct_item_ops;
0335
0336     /* File needs write support.
0337      * The inode's perms must say it's ok,
0338      * and we must have a store method.
0339      */
0340     if (file->f_mode & FMODE_WRITE) {
0341         if (!(inode->i_mode & S_IWUGO))
0342             goto out_put_module;
0343         if ((type & CONFIGFS_ITEM_ATTR) && !attr->store)
0344             goto out_put_module;
0345         if ((type & CONFIGFS_ITEM_BIN_ATTR) && !buffer->bin_attr->write)
0346             goto out_put_module;
0347     }
0348
0349     /* File needs read support.
0350      * The inode's perms must say it's ok, and we there
0351      * must be a show method for it.
0352      */
0353     if (file->f_mode & FMODE_READ) {
0354         if (!(inode->i_mode & S_IRUGO))
0355             goto out_put_module;
0356         if ((type & CONFIGFS_ITEM_ATTR) && !attr->show)
0357             goto out_put_module;
0358         if ((type & CONFIGFS_ITEM_BIN_ATTR) && !buffer->bin_attr->read)
0359             goto out_put_module;
0360     }
0361
0362     mutex_init(&buffer->mutex);
0363     buffer->needs_read_fill = 1;
0364     buffer->read_in_progress = false;
0365     buffer->write_in_progress = false;
0366     file->private_data = buffer;
0367     up_read(&frag->frag_sem);
0368     return 0;
0369
0370 out_put_module:
0371     module_put(buffer->owner);
0372 out_free_buffer:
0373     up_read(&frag->frag_sem);
0374     kfree(buffer);
0375 out:
0376     return error;
0377 }
0378
0379 static int configfs_release(struct inode *inode, struct file *filp)
0380 {
0381     struct configfs_buffer *buffer = filp->private_data;
0382
0383     module_put(buffer->owner);
0384     if (buffer->page)
0385         free_page((unsigned long)buffer->page);
0386     mutex_destroy(&buffer->mutex);
0387     kfree(buffer);
0388     return 0;
0389 }
0390
0391 static int configfs_open_file(struct inode *inode, struct file *filp)
0392 {
0393     return __configfs_open_file(inode, filp, CONFIGFS_ITEM_ATTR);
0394 }
0395
0396 static int configfs_open_bin_file(struct inode *inode, struct file *filp)
0397 {
0398     return __configfs_open_file(inode, filp, CONFIGFS_ITEM_BIN_ATTR);
0399 }
0400
0401 static int configfs_release_bin_file(struct inode *inode, struct file *file)
0402 {
0403     struct configfs_buffer *buffer = file->private_data;
0404
0405     if (buffer->write_in_progress) {
0406         struct configfs_fragment *frag = to_frag(file);
0407
0408         down_read(&frag->frag_sem);
0409         if (!frag->frag_dead) {
0410             /* result of ->release() is ignored */
0411             buffer->bin_attr->write(buffer->item,
0412                     buffer->bin_buffer,
0413                     buffer->bin_buffer_size);
0414         }
0415         up_read(&frag->frag_sem);
0416     }
0417
0418     vfree(buffer->bin_buffer);
0419
0420     configfs_release(inode, file);
0421     return 0;
0422 }
0423
0424
0425 const struct file_operations configfs_file_operations = {
0426     .read_iter  = configfs_read_iter,
0427     .write_iter = configfs_write_iter,
0428     .llseek     = generic_file_llseek,
0429     .open       = configfs_open_file,
0430     .release    = configfs_release,
0431 };
0432
0433 const struct file_operations configfs_bin_file_operations = {
0434     .read_iter  = configfs_bin_read_iter,
0435     .write_iter = configfs_bin_write_iter,
0436     .llseek     = NULL,     /* bin file is not seekable */
0437     .open       = configfs_open_bin_file,
0438     .release    = configfs_release_bin_file,
0439 };
0440
0441 /**
0442  *  configfs_create_file - create an attribute file for an item.
0443  *  @item:  item we're creating for.
0444  *  @attr:  atrribute descriptor.
0445  */
0446
0447 int configfs_create_file(struct config_item * item, const struct configfs_attribute * attr)
0448 {
0449     struct dentry *dir = item->ci_dentry;
0450     struct configfs_dirent *parent_sd = dir->d_fsdata;
0451     umode_t mode = (attr->ca_mode & S_IALLUGO) | S_IFREG;
0452     int error = 0;
0453
0454     inode_lock_nested(d_inode(dir), I_MUTEX_NORMAL);
0455     error = configfs_make_dirent(parent_sd, NULL, (void *) attr, mode,
0456                      CONFIGFS_ITEM_ATTR, parent_sd->s_frag);
0457     inode_unlock(d_inode(dir));
0458
0459     return error;
0460 }
0461
0462 /**
0463  *  configfs_create_bin_file - create a binary attribute file for an item.
0464  *  @item:  item we're creating for.
0465  *  @bin_attr: atrribute descriptor.
0466  */
0467
0468 int configfs_create_bin_file(struct config_item *item,
0469         const struct configfs_bin_attribute *bin_attr)
0470 {
0471     struct dentry *dir = item->ci_dentry;
0472     struct configfs_dirent *parent_sd = dir->d_fsdata;
0473     umode_t mode = (bin_attr->cb_attr.ca_mode & S_IALLUGO) | S_IFREG;
0474     int error = 0;
0475
0476     inode_lock_nested(dir->d_inode, I_MUTEX_NORMAL);
0477     error = configfs_make_dirent(parent_sd, NULL, (void *) bin_attr, mode,
0478                      CONFIGFS_ITEM_BIN_ATTR, parent_sd->s_frag);
0479     inode_unlock(dir->d_inode);
0480
0481     return error;
0482 }