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misc: pass miscdevice through file's private_data

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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>
This commit is contained in:
Tom Van Braeckel 2015-03-31 16:39:21 +02:00 committed by Greg Kroah-Hartman
parent 16c9c8e1ae
commit 0b509d8d33
1 changed files with 8 additions and 3 deletions
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11
drivers/char/misc.c
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@ -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;