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 9cfe53e1e00d..cba4c1c7383c 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);
 }