Commit 0b509d8d authored Mar 31, 2015 by Tom Van Braeckel Committed by Greg Kroah-Hartman Apr 03, 2015

misc: pass miscdevice through file's private_data



Make the miscdevice accessible through the file's private_data.

Previously, this was done only when an open() file operation had been
registered. If no custom open() file operation was defined,
private_data was set to NULL.

This subtle quirk was confusing, to the point where kernel code
registered *empty* file open operations to have private_data point to
the misc device structure and avoid duplicating that logic.

And it could easily lead to bugs, where the addition or removal of a
custom open() file operation surprisingly changes the initial value of
a file's private_data structure.

To resolve this, we now place the miscdevice in the file's private_data
member unconditionally when open() is called.

Signed-off-by: Tom Van Braeckel <tomvanbraeckel@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 16c9c8e1

drivers/char/misc.c

+8 −3

Original line number	Diff line number	Diff line
		@@ -140,12 +140,17 @@ static int misc_open(struct inode * inode, struct file * file)
		goto fail;
		}

		/*
		* Place the miscdevice in the file's
		* private_data so it can be used by the
		* file operations, including f_op->open below
		*/
		file->private_data = c;

		err = 0;
		replace_fops(file, new_fops);
		if (file->f_op->open) {
		file->private_data = c;
		if (file->f_op->open)
		err = file->f_op->open(inode,file);
		}
		fail:
		mutex_unlock(&misc_mtx);
		return err;