Re: [kernel-hardening] [PATCH v2 1/1] Add Trusted Path Execution as a stackable LSM

[Solar Designer <solar@openwall.com>]

Matt,

I really didn't intend to comment on this further, but I just happened
to notice:

On Wed, Jun 07, 2017 at 11:43:49PM -0400, Matt Brown wrote:
> +static int tpe_check(struct file *file, char *method)
> +{
> +	struct inode *inode;
> +	struct inode *file_inode;
> +	struct dentry *dir;
> +	const struct cred *cred = current_cred();
> +	char *reason1 = NULL;
> +	char *reason2 = NULL;
> +
> +	dir = dget_parent(file->f_path.dentry);
> +	inode = d_backing_inode(dir);
> +	file_inode = d_backing_inode(file->f_path.dentry);
> +
> +	if (!tpe_enabled)
> +		return 0;

You have many return statements in tpe_check(), where it is already past
dget_parent() and thus must have reached:

> +end:
> +	dput(dir);

You'll probably want to move the dget_parent() and the following two
lines to be below the first few checks where you may just return, and
then be careful not to ever use a return statement anymore.

Alexander