sysfs: Introduce sysfs_rename_mutex

Looking carefully at the rename code we have a subtle dependency
that the structure of sysfs not change while we are performing
a rename.  If the parent directory of the object we are renaming
changes while the rename is being performed nasty things could
happen when we go to release our locks.

So introduce a sysfs_rename_mutex to prevent this highly
unlikely theoretical issue.

In addition hold sysfs_rename_mutex over all calls to
sysfs_get_dentry. Allowing sysfs_get_dentry to be simplified
in the future.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 16f39c30b091..ff93c92164b3 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -470,7 +470,9 @@ int sysfs_update_file(struct kobject * kobj, const struct attribute * attr)
         if (!victim_sd)
                 goto out;
 
+        mutex_lock(&sysfs_rename_mutex);
         victim = sysfs_get_dentry(victim_sd);
+        mutex_unlock(&sysfs_rename_mutex);
         if (IS_ERR(victim)) {
                 rc = PTR_ERR(victim);
                 victim = NULL;
@@ -509,7 +511,9 @@ int sysfs_chmod_file(struct kobject *kobj, struct attribute *attr, mode_t mode)
         if (!victim_sd)
                 goto out;
 
+        mutex_lock(&sysfs_rename_mutex);
         victim = sysfs_get_dentry(victim_sd);
+        mutex_unlock(&sysfs_rename_mutex);
         if (IS_ERR(victim)) {
                 rc = PTR_ERR(victim);
                 victim = NULL;