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>

1 files changed, 50 insertions, 17 deletions

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 9cfe53e..cba4c1c 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -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);
 }