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![Al Viro](/assets/img/avatar_default.png)
Make sure that attribute methods are not called after the item has been removed from the tree. To do so, we * at the point of no return in removals, grab ->frag_sem exclusive and mark the fragment dead. * call the methods of attributes with ->frag_sem taken shared and only after having verified that the fragment is still alive. The main benefit is for method instances - they are guaranteed that the objects they are accessing *and* all ancestors are still there. Another win is that we don't need to bother with extra refcount on config_item when opening a file - the item will be alive for as long as it stays in the tree, and we won't touch it/attributes/any associated data after it's been removed from the tree. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Christoph Hellwig <hch@lst.de>
556 lines
14 KiB
C
556 lines
14 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/* -*- mode: c; c-basic-offset: 8; -*-
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* vim: noexpandtab sw=8 ts=8 sts=0:
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*
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* file.c - operations for regular (text) files.
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*
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* Based on sysfs:
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* sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
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*
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* configfs Copyright (C) 2005 Oracle. All rights reserved.
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*/
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#include <linux/fs.h>
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#include <linux/module.h>
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#include <linux/slab.h>
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#include <linux/mutex.h>
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#include <linux/vmalloc.h>
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#include <linux/uaccess.h>
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#include <linux/configfs.h>
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#include "configfs_internal.h"
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/*
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* A simple attribute can only be 4096 characters. Why 4k? Because the
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* original code limited it to PAGE_SIZE. That's a bad idea, though,
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* because an attribute of 16k on ia64 won't work on x86. So we limit to
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* 4k, our minimum common page size.
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*/
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#define SIMPLE_ATTR_SIZE 4096
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struct configfs_buffer {
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size_t count;
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loff_t pos;
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char * page;
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struct configfs_item_operations * ops;
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struct mutex mutex;
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int needs_read_fill;
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bool read_in_progress;
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bool write_in_progress;
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char *bin_buffer;
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int bin_buffer_size;
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int cb_max_size;
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struct config_item *item;
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struct module *owner;
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union {
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struct configfs_attribute *attr;
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struct configfs_bin_attribute *bin_attr;
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};
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};
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static inline struct configfs_fragment *to_frag(struct file *file)
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{
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struct configfs_dirent *sd = file->f_path.dentry->d_fsdata;
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return sd->s_frag;
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}
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static int fill_read_buffer(struct file *file, struct configfs_buffer *buffer)
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{
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struct configfs_fragment *frag = to_frag(file);
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ssize_t count = -ENOENT;
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if (!buffer->page)
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buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
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if (!buffer->page)
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return -ENOMEM;
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down_read(&frag->frag_sem);
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if (!frag->frag_dead)
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count = buffer->attr->show(buffer->item, buffer->page);
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up_read(&frag->frag_sem);
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if (count < 0)
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return count;
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if (WARN_ON_ONCE(count > (ssize_t)SIMPLE_ATTR_SIZE))
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return -EIO;
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buffer->needs_read_fill = 0;
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buffer->count = count;
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return 0;
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}
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/**
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* configfs_read_file - read an attribute.
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* @file: file pointer.
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* @buf: buffer to fill.
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* @count: number of bytes to read.
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* @ppos: starting offset in file.
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*
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* Userspace wants to read an attribute file. The attribute descriptor
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* is in the file's ->d_fsdata. The target item is in the directory's
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* ->d_fsdata.
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*
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* We call fill_read_buffer() to allocate and fill the buffer from the
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* item's show() method exactly once (if the read is happening from
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* the beginning of the file). That should fill the entire buffer with
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* all the data the item has to offer for that attribute.
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* We then call flush_read_buffer() to copy the buffer to userspace
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* in the increments specified.
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*/
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static ssize_t
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configfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos)
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{
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struct configfs_buffer *buffer = file->private_data;
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ssize_t retval = 0;
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mutex_lock(&buffer->mutex);
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if (buffer->needs_read_fill) {
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retval = fill_read_buffer(file, buffer);
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if (retval)
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goto out;
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}
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pr_debug("%s: count = %zd, ppos = %lld, buf = %s\n",
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__func__, count, *ppos, buffer->page);
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retval = simple_read_from_buffer(buf, count, ppos, buffer->page,
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buffer->count);
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out:
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mutex_unlock(&buffer->mutex);
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return retval;
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}
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/**
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* configfs_read_bin_file - read a binary attribute.
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* @file: file pointer.
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* @buf: buffer to fill.
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* @count: number of bytes to read.
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* @ppos: starting offset in file.
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*
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* Userspace wants to read a binary attribute file. The attribute
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* descriptor is in the file's ->d_fsdata. The target item is in the
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* directory's ->d_fsdata.
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*
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* We check whether we need to refill the buffer. If so we will
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* call the attributes' attr->read() twice. The first time we
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* will pass a NULL as a buffer pointer, which the attributes' method
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* will use to return the size of the buffer required. If no error
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* occurs we will allocate the buffer using vmalloc and call
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* attr->read() again passing that buffer as an argument.
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* Then we just copy to user-space using simple_read_from_buffer.
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*/
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static ssize_t
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configfs_read_bin_file(struct file *file, char __user *buf,
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size_t count, loff_t *ppos)
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{
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struct configfs_fragment *frag = to_frag(file);
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struct configfs_buffer *buffer = file->private_data;
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ssize_t retval = 0;
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ssize_t len = min_t(size_t, count, PAGE_SIZE);
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mutex_lock(&buffer->mutex);
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/* we don't support switching read/write modes */
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if (buffer->write_in_progress) {
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retval = -ETXTBSY;
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goto out;
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}
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buffer->read_in_progress = true;
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if (buffer->needs_read_fill) {
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/* perform first read with buf == NULL to get extent */
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down_read(&frag->frag_sem);
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if (!frag->frag_dead)
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len = buffer->bin_attr->read(buffer->item, NULL, 0);
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else
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len = -ENOENT;
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up_read(&frag->frag_sem);
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if (len <= 0) {
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retval = len;
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goto out;
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}
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/* do not exceed the maximum value */
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if (buffer->cb_max_size && len > buffer->cb_max_size) {
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retval = -EFBIG;
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goto out;
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}
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buffer->bin_buffer = vmalloc(len);
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if (buffer->bin_buffer == NULL) {
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retval = -ENOMEM;
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goto out;
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}
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buffer->bin_buffer_size = len;
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/* perform second read to fill buffer */
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down_read(&frag->frag_sem);
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if (!frag->frag_dead)
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len = buffer->bin_attr->read(buffer->item,
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buffer->bin_buffer, len);
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else
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len = -ENOENT;
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up_read(&frag->frag_sem);
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if (len < 0) {
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retval = len;
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vfree(buffer->bin_buffer);
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buffer->bin_buffer_size = 0;
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buffer->bin_buffer = NULL;
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goto out;
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}
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buffer->needs_read_fill = 0;
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}
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retval = simple_read_from_buffer(buf, count, ppos, buffer->bin_buffer,
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buffer->bin_buffer_size);
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out:
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mutex_unlock(&buffer->mutex);
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return retval;
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}
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/**
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* fill_write_buffer - copy buffer from userspace.
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* @buffer: data buffer for file.
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* @buf: data from user.
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* @count: number of bytes in @userbuf.
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*
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* Allocate @buffer->page if it hasn't been already, then
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* copy the user-supplied buffer into it.
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*/
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static int
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fill_write_buffer(struct configfs_buffer * buffer, const char __user * buf, size_t count)
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{
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int error;
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if (!buffer->page)
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buffer->page = (char *)__get_free_pages(GFP_KERNEL, 0);
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if (!buffer->page)
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return -ENOMEM;
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if (count >= SIMPLE_ATTR_SIZE)
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count = SIMPLE_ATTR_SIZE - 1;
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error = copy_from_user(buffer->page,buf,count);
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buffer->needs_read_fill = 1;
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/* if buf is assumed to contain a string, terminate it by \0,
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* so e.g. sscanf() can scan the string easily */
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buffer->page[count] = 0;
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return error ? -EFAULT : count;
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}
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static int
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flush_write_buffer(struct file *file, struct configfs_buffer *buffer, size_t count)
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{
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struct configfs_fragment *frag = to_frag(file);
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int res = -ENOENT;
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down_read(&frag->frag_sem);
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if (!frag->frag_dead)
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res = buffer->attr->store(buffer->item, buffer->page, count);
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up_read(&frag->frag_sem);
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return res;
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}
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/**
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* configfs_write_file - write an attribute.
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* @file: file pointer
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* @buf: data to write
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* @count: number of bytes
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* @ppos: starting offset
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*
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* Similar to configfs_read_file(), though working in the opposite direction.
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* We allocate and fill the data from the user in fill_write_buffer(),
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* then push it to the config_item in flush_write_buffer().
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* There is no easy way for us to know if userspace is only doing a partial
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* write, so we don't support them. We expect the entire buffer to come
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* on the first write.
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* Hint: if you're writing a value, first read the file, modify only the
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* the value you're changing, then write entire buffer back.
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*/
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static ssize_t
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configfs_write_file(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
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{
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struct configfs_buffer *buffer = file->private_data;
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ssize_t len;
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mutex_lock(&buffer->mutex);
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len = fill_write_buffer(buffer, buf, count);
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if (len > 0)
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len = flush_write_buffer(file, buffer, len);
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if (len > 0)
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*ppos += len;
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mutex_unlock(&buffer->mutex);
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return len;
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}
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/**
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* configfs_write_bin_file - write a binary attribute.
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* @file: file pointer
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* @buf: data to write
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* @count: number of bytes
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* @ppos: starting offset
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*
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* Writing to a binary attribute file is similar to a normal read.
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* We buffer the consecutive writes (binary attribute files do not
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* support lseek) in a continuously growing buffer, but we don't
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* commit until the close of the file.
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*/
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static ssize_t
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configfs_write_bin_file(struct file *file, const char __user *buf,
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size_t count, loff_t *ppos)
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{
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struct configfs_buffer *buffer = file->private_data;
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void *tbuf = NULL;
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ssize_t len;
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mutex_lock(&buffer->mutex);
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/* we don't support switching read/write modes */
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if (buffer->read_in_progress) {
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len = -ETXTBSY;
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goto out;
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}
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buffer->write_in_progress = true;
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/* buffer grows? */
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if (*ppos + count > buffer->bin_buffer_size) {
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if (buffer->cb_max_size &&
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*ppos + count > buffer->cb_max_size) {
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len = -EFBIG;
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goto out;
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}
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tbuf = vmalloc(*ppos + count);
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if (tbuf == NULL) {
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len = -ENOMEM;
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goto out;
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}
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/* copy old contents */
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if (buffer->bin_buffer) {
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memcpy(tbuf, buffer->bin_buffer,
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buffer->bin_buffer_size);
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vfree(buffer->bin_buffer);
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}
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/* clear the new area */
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memset(tbuf + buffer->bin_buffer_size, 0,
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*ppos + count - buffer->bin_buffer_size);
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buffer->bin_buffer = tbuf;
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buffer->bin_buffer_size = *ppos + count;
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}
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len = simple_write_to_buffer(buffer->bin_buffer,
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buffer->bin_buffer_size, ppos, buf, count);
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out:
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mutex_unlock(&buffer->mutex);
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return len;
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}
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static int __configfs_open_file(struct inode *inode, struct file *file, int type)
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{
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struct dentry *dentry = file->f_path.dentry;
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struct configfs_fragment *frag = to_frag(file);
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struct configfs_attribute *attr;
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struct configfs_buffer *buffer;
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int error;
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error = -ENOMEM;
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buffer = kzalloc(sizeof(struct configfs_buffer), GFP_KERNEL);
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if (!buffer)
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goto out;
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error = -ENOENT;
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down_read(&frag->frag_sem);
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if (unlikely(frag->frag_dead))
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goto out_free_buffer;
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error = -EINVAL;
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buffer->item = to_item(dentry->d_parent);
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if (!buffer->item)
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goto out_free_buffer;
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attr = to_attr(dentry);
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if (!attr)
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goto out_put_item;
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if (type & CONFIGFS_ITEM_BIN_ATTR) {
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buffer->bin_attr = to_bin_attr(dentry);
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buffer->cb_max_size = buffer->bin_attr->cb_max_size;
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} else {
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buffer->attr = attr;
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}
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buffer->owner = attr->ca_owner;
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/* Grab the module reference for this attribute if we have one */
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error = -ENODEV;
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if (!try_module_get(buffer->owner))
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goto out_put_item;
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error = -EACCES;
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if (!buffer->item->ci_type)
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goto out_put_module;
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buffer->ops = buffer->item->ci_type->ct_item_ops;
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/* File needs write support.
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* The inode's perms must say it's ok,
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* and we must have a store method.
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*/
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if (file->f_mode & FMODE_WRITE) {
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if (!(inode->i_mode & S_IWUGO))
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goto out_put_module;
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if ((type & CONFIGFS_ITEM_ATTR) && !attr->store)
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goto out_put_module;
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if ((type & CONFIGFS_ITEM_BIN_ATTR) && !buffer->bin_attr->write)
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goto out_put_module;
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}
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/* File needs read support.
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* The inode's perms must say it's ok, and we there
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* must be a show method for it.
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*/
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if (file->f_mode & FMODE_READ) {
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if (!(inode->i_mode & S_IRUGO))
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goto out_put_module;
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if ((type & CONFIGFS_ITEM_ATTR) && !attr->show)
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goto out_put_module;
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if ((type & CONFIGFS_ITEM_BIN_ATTR) && !buffer->bin_attr->read)
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goto out_put_module;
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}
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mutex_init(&buffer->mutex);
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buffer->needs_read_fill = 1;
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buffer->read_in_progress = false;
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buffer->write_in_progress = false;
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file->private_data = buffer;
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up_read(&frag->frag_sem);
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return 0;
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out_put_module:
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module_put(buffer->owner);
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out_put_item:
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config_item_put(buffer->item);
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out_free_buffer:
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up_read(&frag->frag_sem);
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kfree(buffer);
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out:
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return error;
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}
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static int configfs_release(struct inode *inode, struct file *filp)
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{
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struct configfs_buffer *buffer = filp->private_data;
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module_put(buffer->owner);
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if (buffer->page)
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free_page((unsigned long)buffer->page);
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mutex_destroy(&buffer->mutex);
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kfree(buffer);
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return 0;
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}
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static int configfs_open_file(struct inode *inode, struct file *filp)
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{
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return __configfs_open_file(inode, filp, CONFIGFS_ITEM_ATTR);
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}
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static int configfs_open_bin_file(struct inode *inode, struct file *filp)
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{
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return __configfs_open_file(inode, filp, CONFIGFS_ITEM_BIN_ATTR);
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}
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static int configfs_release_bin_file(struct inode *inode, struct file *file)
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{
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struct configfs_buffer *buffer = file->private_data;
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buffer->read_in_progress = false;
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if (buffer->write_in_progress) {
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struct configfs_fragment *frag = to_frag(file);
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buffer->write_in_progress = false;
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down_read(&frag->frag_sem);
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if (!frag->frag_dead) {
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/* result of ->release() is ignored */
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buffer->bin_attr->write(buffer->item,
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buffer->bin_buffer,
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buffer->bin_buffer_size);
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}
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up_read(&frag->frag_sem);
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/* vfree on NULL is safe */
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vfree(buffer->bin_buffer);
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buffer->bin_buffer = NULL;
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buffer->bin_buffer_size = 0;
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buffer->needs_read_fill = 1;
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}
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configfs_release(inode, file);
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return 0;
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}
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const struct file_operations configfs_file_operations = {
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.read = configfs_read_file,
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.write = configfs_write_file,
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.llseek = generic_file_llseek,
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.open = configfs_open_file,
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.release = configfs_release,
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};
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const struct file_operations configfs_bin_file_operations = {
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.read = configfs_read_bin_file,
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.write = configfs_write_bin_file,
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.llseek = NULL, /* bin file is not seekable */
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.open = configfs_open_bin_file,
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.release = configfs_release_bin_file,
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};
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/**
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* configfs_create_file - create an attribute file for an item.
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* @item: item we're creating for.
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* @attr: atrribute descriptor.
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*/
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int configfs_create_file(struct config_item * item, const struct configfs_attribute * attr)
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{
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struct dentry *dir = item->ci_dentry;
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struct configfs_dirent *parent_sd = dir->d_fsdata;
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umode_t mode = (attr->ca_mode & S_IALLUGO) | S_IFREG;
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int error = 0;
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inode_lock_nested(d_inode(dir), I_MUTEX_NORMAL);
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error = configfs_make_dirent(parent_sd, NULL, (void *) attr, mode,
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CONFIGFS_ITEM_ATTR, parent_sd->s_frag);
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inode_unlock(d_inode(dir));
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return error;
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}
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/**
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* configfs_create_bin_file - create a binary attribute file for an item.
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* @item: item we're creating for.
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* @attr: atrribute descriptor.
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*/
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int configfs_create_bin_file(struct config_item *item,
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const struct configfs_bin_attribute *bin_attr)
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{
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struct dentry *dir = item->ci_dentry;
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struct configfs_dirent *parent_sd = dir->d_fsdata;
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umode_t mode = (bin_attr->cb_attr.ca_mode & S_IALLUGO) | S_IFREG;
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int error = 0;
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inode_lock_nested(dir->d_inode, I_MUTEX_NORMAL);
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error = configfs_make_dirent(parent_sd, NULL, (void *) bin_attr, mode,
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CONFIGFS_ITEM_BIN_ATTR, parent_sd->s_frag);
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inode_unlock(dir->d_inode);
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return error;
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}
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