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Message-ID: <4EF16DE1.8010909@canonical.com>
Date: Tue, 20 Dec 2011 21:25:53 -0800
From: John Johansen <john.johansen@...onical.com>
To: kernel-hardening@...ts.openwall.com
CC: Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org,
linux-security-module@...r.kernel.org,
Roland McGrath <roland@...k.frob.com>,
James Morris <jmorris@...ei.org>
Subject: Re: [kernel-hardening] [PATCH 2/2] security: Yama LSM
On 12/19/2011 02:17 PM, Kees Cook wrote:
> This adds the Yama Linux Security Module to collect DAC security
> improvements (specifically just ptrace restrictions for now) that have
> existed in various forms over the years and have been carried outside the
> mainline kernel by other Linux distributions like Openwall and grsecurity.
>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> v9:
> - Remove pid_ns feature. Touches too many core kernel areas at the moment.
> v8:
> - Updated RCU usage and locking, thanks to Mandeep Singh Baines.
> v7:
> - Merge ptrace restrictions, which include various fixes from
> Vasiliy Kulikov, Solar Designer, Ming Lei, Tetsuo Handa, and Eric Paris.
> - Merge pid_ns feature from Vasiliy Kulikov.
> - Rip out link restrictions for initial upstreaming.
> v6:
> - Fix interaction with overlayfs, thanks to Andy Whitcroft and Leann
> Ogasawara.
> - Clarify rationale for LSM.
> - Move documentation under security subdirectory.
> v5:
> - resend, with ptrace relationship interface
> v4:
> - drop accidentally included fs/exec.c chunk.
> v3:
> - drop needless cap_ callbacks.
> - fix usage of get_task_comm.
> - drop CONFIG_ of sysctl defaults, as recommended by Andi Kleen.
> - require SYSCTL.
> v2:
> - add rcu locking, thanks to Tetsuo Handa.
> - add Documentation/Yama.txt for summary of features.
This is looking really good. I have a few notes inlined below but I didn't
find any problems.
I am happy giving it an
Acked-by: John Johansen <john.johansen@...onical.com>
or Reviewed-by: if that is more appropriate here
<snip>
> index 0000000..1029fcd
> --- /dev/null
> +++ b/security/yama/yama_lsm.c
> @@ -0,0 +1,315 @@
> +/*
> + * Yama Linux Security Module
> + *
> + * Author: Kees Cook <keescook@...omium.org>
> + *
> + * Copyright (C) 2010 Canonical, Ltd.
> + * Copyright (C) 2011 The Chromium OS Authors.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2, as
> + * published by the Free Software Foundation.
> + *
> + */
> +
> +#include <linux/security.h>
> +#include <linux/sysctl.h>
> +#include <linux/ptrace.h>
> +#include <linux/prctl.h>
> +#include <linux/ratelimit.h>
> +
> +static int ptrace_scope = 1;
> +
> +/* describe a ptrace relationship for potential exception */
> +struct ptrace_relation {
> + struct task_struct *tracer;
> + struct task_struct *tracee;
> + struct list_head node;
> +};
> +
> +static LIST_HEAD(ptracer_relations);
> +static DEFINE_SPINLOCK(ptracer_relations_lock);
> +
> +/**
> + * yama_ptracer_add - add/replace an exception for this tracer/tracee pair
> + * @tracer: the task_struct of the process doing the ptrace
> + * @tracee: the task_struct of the process to be ptraced
> + *
> + * Returns 0 if relationship was added, -ve on error.
> + */
It might be good to add a note here, or a more explicit note in the Yama
Documentation that a tracee can only have a single tracer (+ its descendants).
In the documentation
An inferior can declare which other process (and its descendents) are allowed
to call PTRACE_ATTACH against it
Its real easy to not catch its process instead of processes
> +static int yama_ptracer_add(struct task_struct *tracer,
> + struct task_struct *tracee)
> +{
> + int rc = 0;
> + struct ptrace_relation *added;
> + struct ptrace_relation *entry, *relation = NULL;
> +
> + added = kmalloc(sizeof(*added), GFP_KERNEL);
> + spin_lock_bh(&ptracer_relations_lock);
> + list_for_each_entry(entry, &ptracer_relations, node)
> + if (entry->tracee == tracee) {
> + relation = entry;
> + break;
> + }
> + if (!relation) {
> + relation = added;
> + if (!relation) {
> + rc = -ENOMEM;
> + goto unlock_out;
> + }
> + relation->tracee = tracee;
> + list_add(&relation->node, &ptracer_relations);
> + }
> + relation->tracer = tracer;
> +
> +unlock_out:
> + spin_unlock_bh(&ptracer_relations_lock);
> + if (added && added != relation)
> + kfree(added);
> +
> + return rc;
> +}
> +
I think pulling the out of the locking makes the fn a little easier to
read.
static int yama_ptracer_add(struct task_struct *tracer,
struct task_struct *tracee)
{
int rc = 0;
struct ptrace_relation *added;
struct ptrace_relation *entry, *relation = NULL;
added = kmalloc(sizeof(*added), GFP_KERNEL);
if (!added)
return -ENOMEM;
spin_lock_bh(&ptracer_relations_lock);
list_for_each_entry(entry, &ptracer_relations, node)
if (entry->tracee == tracee) {
relation = entry;
break;
}
if (!relation) {
relation = added;
relation->tracee = tracee;
list_add(&relation->node, &ptracer_relations);
}
relation->tracer = tracer;
spin_unlock_bh(&ptracer_relations_lock);
if (added != relation)
kfree(added);
return rc;
}
or if you prefer to keep a single exit point
static int yama_ptracer_add(struct task_struct *tracer,
struct task_struct *tracee)
{
int rc = -ENOMEM;
struct ptrace_relation *added;
struct ptrace_relation *entry, *relation = NULL;
added = kmalloc(sizeof(*added), GFP_KERNEL);
if (!added)
goto out;
spin_lock_bh(&ptracer_relations_lock);
list_for_each_entry(entry, &ptracer_relations, node)
if (entry->tracee == tracee) {
relation = entry;
break;
}
if (!relation) {
relation = added;
relation->tracee = tracee;
list_add(&relation->node, &ptracer_relations);
}
relation->tracer = tracer;
spin_unlock_bh(&ptracer_relations_lock);
if (added != relation)
kfree(added);
rc = 0;
out:
return rc;
}
> +/**
> + * yama_ptracer_del - remove exceptions related to the given tasks
> + * @tracer: remove any relation where tracer task matches
> + * @tracee: remove any relation where tracee task matches
> + */
> +static void yama_ptracer_del(struct task_struct *tracer,
> + struct task_struct *tracee)
> +{
> + struct ptrace_relation *relation;
> + struct list_head *list, *safe;
> +
> + spin_lock_bh(&ptracer_relations_lock);
> + list_for_each_safe(list, safe, &ptracer_relations) {
> + relation = list_entry(list, struct ptrace_relation, node);
You could use list_for_each_entry_safe here
list_for_each_entry_safe(relation, safe, &ptracer_relations, node)
> + if (relation->tracee == tracee ||
> + relation->tracer == tracer) {
> + list_del(&relation->node);
> + kfree(relation);
> + }
> + }
> + spin_unlock_bh(&ptracer_relations_lock);
> +}
> +
> +/**
> + * yama_task_free - check for task_pid to remove from exception list
> + * @task: task being removed
> + */
> +static void yama_task_free(struct task_struct *task)
> +{
> + yama_ptracer_del(task, task);
> +}
> +
> +/**
> + * yama_task_prctl - check for Yama-specific prctl operations
> + * @option: operation
> + * @arg2: argument
> + * @arg3: argument
> + * @arg4: argument
> + * @arg5: argument
> + *
> + * Return 0 on success, -ve on error. -ENOSYS is returned when Yama
> + * does not handle the given option.
> + */
So maybe add a note here about why the tracee is being stored via the
group_leader, but that the tracer isn't. Its not really a problem but I
tripped over this at first as I was going through the code.
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