From: Tom Van Braeckel <tomvanbraeckel@gmail.com>
Date: Tue, 31 Mar 2015 14:39:21 +0000 (+0200)
Subject: misc: pass miscdevice through file's private_data
X-Git-Tag: firefly_0821_release~176^2~1906^2~30
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=0b509d8d336eef6d622d66b3ae2a1fc3a072bf92;p=firefly-linux-kernel-4.4.55.git

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>
---

diff --git a/drivers/char/misc.c b/drivers/char/misc.c
index 5bb3a2109ab7..9fd5a91e0d81 100644
--- a/drivers/char/misc.c
+++ b/drivers/char/misc.c
@@ -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;