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>

8 files changed, 103 insertions, 17 deletions

diff --git a/fs/sysfs/bin.c b/fs/sysfs/bin.c
index e8f540d38d48..9ec1c8539a5d 100644
--- a/fs/sysfs/bin.c
+++ b/fs/sysfs/bin.c
@@ -16,6 +16,7 @@
 #include <linux/slab.h>
 
 #include <asm/uaccess.h>
+#include <asm/semaphore.h>
 
 #include "sysfs.h"
 
diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 2bab1b4ddf5a..9ff04491e3ea 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -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);
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);
 }
 
 
diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c
index 122145b0895c..46a277b0838e 100644
--- a/fs/sysfs/group.c
+++ b/fs/sysfs/group.c
@@ -13,6 +13,7 @@
 #include <linux/dcache.h>
 #include <linux/namei.h>
 #include <linux/err.h>
+#include <asm/semaphore.h>
 #include "sysfs.h"
 
 
diff --git a/fs/sysfs/inode.c b/fs/sysfs/inode.c
index e79e38d52c00..1a81ebce20e9 100644
--- a/fs/sysfs/inode.c
+++ b/fs/sysfs/inode.c
@@ -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);
diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index e503f858fba8..a1a58b97f322 100644
--- a/fs/sysfs/mount.c
+++ b/fs/sysfs/mount.c
@@ -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;
diff --git a/fs/sysfs/symlink.c b/fs/sysfs/symlink.c
index f50e3cc2ded8..4869f611192f 100644
--- a/fs/sysfs/symlink.c
+++ b/fs/sysfs/symlink.c
@@ -7,6 +7,7 @@
 #include <linux/module.h>
 #include <linux/kobject.h>
 #include <linux/namei.h>
+#include <asm/semaphore.h>
 
 #include "sysfs.h"
 
diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index bd7cec295dab..39c623fdc277 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -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;