[fuse] fix race between checking and setting file->private_data

BKL does not protect against races if the task may sleep between
checking and setting a value.  So move checking of file->private_data
near to setting it in fuse_fill_super().

Found by Al Viro.

Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index fd34037..7627022 100644 (file)
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -500,11 +500,6 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
        if (file->f_op != &fuse_dev_operations)
                return -EINVAL;
 
-       /* Setting file->private_data can't race with other mount()
-          instances, since BKL is held for ->get_sb() */
-       if (file->private_data)
-               return -EINVAL;
-
        fc = new_conn();
        if (!fc)
                return -ENOMEM;
@@ -540,6 +535,12 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
        if (err)
                goto err_free_req;
 
+       /* Setting file->private_data can't race with other mount()
+          instances, since BKL is held for ->get_sb() */
+       err = -EINVAL;
+       if (file->private_data)
+               goto err_kobject_del;
+
        sb->s_root = root_dentry;
        fc->mounted = 1;
        fc->connected = 1;
@@ -556,6 +557,8 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
 
        return 0;
 
+ err_kobject_del:
+       kobject_del(&fc->kobj);
  err_free_req:
        fuse_request_free(init_req);
  err_put_root: