Re: [PATCH v2 5/5] LSM: LoadPin for kernel file loading restrictions

[Andrew Morton]

On Mon, 28 Mar 2016 14:14:22 -0700 Kees Cook <keescook@xxxxxxxxxxxx> wrote:

> This LSM enforces that kernel-loaded files (modules, firmware, etc)
> must all come from the same filesystem, with the expectation that
> such a filesystem is backed by a read-only device such as dm-verity
> or CDROM. This allows systems that have a verified and/or unchangeable
> filesystem to enforce module and firmware loading restrictions without
> needing to sign the files individually.

Patchset generally looks good to me.  It's regrettable that a load of
stuff was added to lib/ for one obscure LSM but hopefully (doubtfully)
someone else will find a use for some of it.

I'll assume that James is handling all of this.

> --- /dev/null
> +++ b/security/loadpin/loadpin.c
> @@ -0,0 +1,206 @@
> +/*
> + * Module and Firmware Pinning Security Module
> + *
> + * Copyright 2011-2016 Google Inc.
> + *
> + * Author: Kees Cook <keescook@xxxxxxxxxxxx>
> + *
> + * This software is licensed under the terms of the GNU General Public
> + * License version 2, as published by the Free Software Foundation, and
> + * may be copied, distributed, and modified under those terms.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + */
> +
> +#define pr_fmt(fmt) "LoadPin: " fmt
> +
> +#include <linux/module.h>
> +#include <linux/fs.h>
> +#include <linux/fs_struct.h>
> +#include <linux/lsm_hooks.h>
> +#include <linux/mount.h>
> +#include <linux/path.h>
> +#include <linux/sched.h>	/* current */
> +#include <linux/string_helpers.h>
> +
> +static void report_load(const char *origin, struct file *file, char *operation)
> +{
> +	char *cmdline, *pathname;
> +
> +	pathname = kstrdup_quotable_file(file);
> +	cmdline = kstrdup_quotable_cmdline(current);
> +
> +	pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n",
> +		  origin, operation,
> +		  (pathname && pathname[0] != '<') ? "\"" : "",
> +		  pathname,
> +		  (pathname && pathname[0] != '<') ? "\"" : "",
> +		  task_pid_nr(current),
> +		  cmdline ? "\"" : "", cmdline, cmdline ? "\"" : "");
> +
> +	kfree(cmdline);
> +	kfree(pathname);
> +}
> +
> +static int load_pinning = 1;
> +static struct super_block *pinned_root;
> +static DEFINE_SPINLOCK(pinned_root_spinlock);
> +
> +#ifdef CONFIG_SYSCTL
> +static int zero;
> +static int one = 1;
> +
> +static struct ctl_path loadpin_sysctl_path[] = {
> +	{ .procname = "kernel", },
> +	{ }
> +};
> +
> +static struct ctl_table loadpin_sysctl_table[] = {
> +	{
> +		.procname       = "load_pinning",
> +		.data           = &load_pinning,
> +		.maxlen         = sizeof(int),
> +		.mode           = 0644,
> +		.proc_handler   = proc_dointvec_minmax,
> +		.extra1         = &zero,
> +		.extra2         = &one,
> +	},
> +	{ }
> +};

There should be somewhere to document the new sysctl?