Driver core: fix race in sysfs between sysfs_remove_file() and read()/write()

This patch prevents a race between IO and removing a file from sysfs.
It introduces a list of sysfs_buffers associated with a file at the inode.
Upon removal of a file the list is walked and the buffers marked orphaned.
IO to orphaned buffers fails with -ENODEV. The driver can safely free
associated data structures or be unloaded.

Signed-off-by: Oliver Neukum <oliver@neukum.name>
Acked-by: Maneesh Soni <maneesh@in.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Oliver Neukum 2006-12-20 10:52:44 +01:00 committed by Greg Kroah-Hartman
parent cb986b749c
commit 94bebf4d1b
8 changed files with 103 additions and 17 deletions

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@ -16,6 +16,7 @@
#include <linux/slab.h>
#include <asm/uaccess.h>
#include <asm/semaphore.h>
#include "sysfs.h"

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@ -9,6 +9,7 @@
#include <linux/module.h>
#include <linux/kobject.h>
#include <linux/namei.h>
#include <asm/semaphore.h>
#include "sysfs.h"
DECLARE_RWSEM(sysfs_rename_sem);

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@ -7,6 +7,7 @@
#include <linux/kobject.h>
#include <linux/namei.h>
#include <linux/poll.h>
#include <linux/list.h>
#include <asm/uaccess.h>
#include <asm/semaphore.h>
@ -50,17 +51,29 @@ static struct sysfs_ops subsys_sysfs_ops = {
.store = subsys_attr_store,
};
/**
* add_to_collection - add buffer to a collection
* @buffer: buffer to be added
* @node inode of set to add to
*/
struct sysfs_buffer {
size_t count;
loff_t pos;
char * page;
struct sysfs_ops * ops;
struct semaphore sem;
int needs_read_fill;
int event;
};
static inline void
add_to_collection(struct sysfs_buffer *buffer, struct inode *node)
{
struct sysfs_buffer_collection *set = node->i_private;
mutex_lock(&node->i_mutex);
list_add(&buffer->associates, &set->associates);
mutex_unlock(&node->i_mutex);
}
static inline void
remove_from_collection(struct sysfs_buffer *buffer, struct inode *node)
{
mutex_lock(&node->i_mutex);
list_del(&buffer->associates);
mutex_unlock(&node->i_mutex);
}
/**
* fill_read_buffer - allocate and fill buffer from object.
@ -153,6 +166,10 @@ sysfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos)
ssize_t retval = 0;
down(&buffer->sem);
if (buffer->orphaned) {
retval = -ENODEV;
goto out;
}
if (buffer->needs_read_fill) {
if ((retval = fill_read_buffer(file->f_path.dentry,buffer)))
goto out;
@ -165,7 +182,6 @@ out:
return retval;
}
/**
* fill_write_buffer - copy buffer from userspace.
* @buffer: data buffer for file.
@ -243,19 +259,25 @@ sysfs_write_file(struct file *file, const char __user *buf, size_t count, loff_t
ssize_t len;
down(&buffer->sem);
if (buffer->orphaned) {
len = -ENODEV;
goto out;
}
len = fill_write_buffer(buffer, buf, count);
if (len > 0)
len = flush_write_buffer(file->f_path.dentry, buffer, len);
if (len > 0)
*ppos += len;
out:
up(&buffer->sem);
return len;
}
static int check_perm(struct inode * inode, struct file * file)
static int sysfs_open_file(struct inode *inode, struct file *file)
{
struct kobject *kobj = sysfs_get_kobject(file->f_path.dentry->d_parent);
struct attribute * attr = to_attr(file->f_path.dentry);
struct sysfs_buffer_collection *set;
struct sysfs_buffer * buffer;
struct sysfs_ops * ops = NULL;
int error = 0;
@ -285,6 +307,18 @@ static int check_perm(struct inode * inode, struct file * file)
if (!ops)
goto Eaccess;
/* make sure we have a collection to add our buffers to */
mutex_lock(&inode->i_mutex);
if (!(set = inode->i_private)) {
if (!(set = inode->i_private = kmalloc(sizeof(struct sysfs_buffer_collection), GFP_KERNEL))) {
error = -ENOMEM;
goto Done;
} else {
INIT_LIST_HEAD(&set->associates);
}
}
mutex_unlock(&inode->i_mutex);
/* File needs write support.
* The inode's perms must say it's ok,
* and we must have a store method.
@ -310,9 +344,11 @@ static int check_perm(struct inode * inode, struct file * file)
*/
buffer = kzalloc(sizeof(struct sysfs_buffer), GFP_KERNEL);
if (buffer) {
INIT_LIST_HEAD(&buffer->associates);
init_MUTEX(&buffer->sem);
buffer->needs_read_fill = 1;
buffer->ops = ops;
add_to_collection(buffer, inode);
file->private_data = buffer;
} else
error = -ENOMEM;
@ -330,11 +366,6 @@ static int check_perm(struct inode * inode, struct file * file)
return error;
}
static int sysfs_open_file(struct inode * inode, struct file * filp)
{
return check_perm(inode,filp);
}
static int sysfs_release(struct inode * inode, struct file * filp)
{
struct kobject * kobj = to_kobj(filp->f_path.dentry->d_parent);
@ -342,6 +373,8 @@ static int sysfs_release(struct inode * inode, struct file * filp)
struct module * owner = attr->owner;
struct sysfs_buffer * buffer = filp->private_data;
if (buffer)
remove_from_collection(buffer, inode);
if (kobj)
kobject_put(kobj);
/* After this point, attr should not be accessed. */
@ -548,7 +581,7 @@ EXPORT_SYMBOL_GPL(sysfs_chmod_file);
void sysfs_remove_file(struct kobject * kobj, const struct attribute * attr)
{
sysfs_hash_and_remove(kobj->dentry,attr->name);
sysfs_hash_and_remove(kobj->dentry, attr->name);
}

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@ -13,6 +13,7 @@
#include <linux/dcache.h>
#include <linux/namei.h>
#include <linux/err.h>
#include <asm/semaphore.h>
#include "sysfs.h"

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@ -13,6 +13,7 @@
#include <linux/backing-dev.h>
#include <linux/capability.h>
#include <linux/errno.h>
#include <asm/semaphore.h>
#include "sysfs.h"
extern struct super_block * sysfs_sb;
@ -209,6 +210,22 @@ const unsigned char * sysfs_get_name(struct sysfs_dirent *sd)
return NULL;
}
static inline void orphan_all_buffers(struct inode *node)
{
struct sysfs_buffer_collection *set = node->i_private;
struct sysfs_buffer *buf;
mutex_lock(&node->i_mutex);
if (node->i_private) {
list_for_each_entry(buf, &set->associates, associates) {
down(&buf->sem);
buf->orphaned = 1;
up(&buf->sem);
}
}
mutex_unlock(&node->i_mutex);
}
/*
* Unhashes the dentry corresponding to given sysfs_dirent
@ -217,16 +234,23 @@ const unsigned char * sysfs_get_name(struct sysfs_dirent *sd)
void sysfs_drop_dentry(struct sysfs_dirent * sd, struct dentry * parent)
{
struct dentry * dentry = sd->s_dentry;
struct inode *inode;
if (dentry) {
spin_lock(&dcache_lock);
spin_lock(&dentry->d_lock);
if (!(d_unhashed(dentry) && dentry->d_inode)) {
inode = dentry->d_inode;
spin_lock(&inode->i_lock);
__iget(inode);
spin_unlock(&inode->i_lock);
dget_locked(dentry);
__d_drop(dentry);
spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
simple_unlink(parent->d_inode, dentry);
orphan_all_buffers(inode);
iput(inode);
} else {
spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);

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@ -8,6 +8,7 @@
#include <linux/mount.h>
#include <linux/pagemap.h>
#include <linux/init.h>
#include <asm/semaphore.h>
#include "sysfs.h"
@ -18,9 +19,12 @@ struct vfsmount *sysfs_mount;
struct super_block * sysfs_sb = NULL;
struct kmem_cache *sysfs_dir_cachep;
static void sysfs_clear_inode(struct inode *inode);
static struct super_operations sysfs_ops = {
.statfs = simple_statfs,
.drop_inode = generic_delete_inode,
.clear_inode = sysfs_clear_inode,
};
static struct sysfs_dirent sysfs_root = {
@ -31,6 +35,11 @@ static struct sysfs_dirent sysfs_root = {
.s_iattr = NULL,
};
static void sysfs_clear_inode(struct inode *inode)
{
kfree(inode->i_private);
}
static int sysfs_fill_super(struct super_block *sb, void *data, int silent)
{
struct inode *inode;

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@ -7,6 +7,7 @@
#include <linux/module.h>
#include <linux/kobject.h>
#include <linux/namei.h>
#include <asm/semaphore.h>
#include "sysfs.h"

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@ -33,6 +33,22 @@ struct sysfs_symlink {
struct kobject * target_kobj;
};
struct sysfs_buffer {
struct list_head associates;
size_t count;
loff_t pos;
char * page;
struct sysfs_ops * ops;
struct semaphore sem;
int orphaned;
int needs_read_fill;
int event;
};
struct sysfs_buffer_collection {
struct list_head associates;
};
static inline struct kobject * to_kobj(struct dentry * dentry)
{
struct sysfs_dirent * sd = dentry->d_fsdata;