![Casey Schaufler](/assets/img/avatar_default.png)
I am still tired of having to find indirect ways to determine what security modules are active on a system. I have added /sys/kernel/security/lsm, which contains a comma separated list of the active security modules. No more groping around in /proc/filesystems or other clever hacks. Unchanged from previous versions except for being updated to the latest security next branch. Signed-off-by: Casey Schaufler <casey@schaufler-ca.com> Acked-by: John Johansen <john.johansen@canonical.com> Acked-by: Paul Moore <paul@paul-moore.com> Acked-by: Kees Cook <keescook@chromium.org> Signed-off-by: James Morris <james.l.morris@oracle.com>
491 lines
12 KiB
C
491 lines
12 KiB
C
/*
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* Yama Linux Security Module
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*
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* Author: Kees Cook <keescook@chromium.org>
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*
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* Copyright (C) 2010 Canonical, Ltd.
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* Copyright (C) 2011 The Chromium OS Authors.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2, as
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* published by the Free Software Foundation.
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*
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*/
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#include <linux/lsm_hooks.h>
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#include <linux/sysctl.h>
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#include <linux/ptrace.h>
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#include <linux/prctl.h>
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#include <linux/ratelimit.h>
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#include <linux/workqueue.h>
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#include <linux/string_helpers.h>
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#include <linux/task_work.h>
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#include <linux/sched.h>
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#include <linux/spinlock.h>
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#define YAMA_SCOPE_DISABLED 0
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#define YAMA_SCOPE_RELATIONAL 1
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#define YAMA_SCOPE_CAPABILITY 2
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#define YAMA_SCOPE_NO_ATTACH 3
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static int ptrace_scope = YAMA_SCOPE_RELATIONAL;
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/* describe a ptrace relationship for potential exception */
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struct ptrace_relation {
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struct task_struct *tracer;
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struct task_struct *tracee;
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bool invalid;
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struct list_head node;
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struct rcu_head rcu;
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};
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static LIST_HEAD(ptracer_relations);
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static DEFINE_SPINLOCK(ptracer_relations_lock);
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static void yama_relation_cleanup(struct work_struct *work);
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static DECLARE_WORK(yama_relation_work, yama_relation_cleanup);
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struct access_report_info {
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struct callback_head work;
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const char *access;
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struct task_struct *target;
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struct task_struct *agent;
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};
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static void __report_access(struct callback_head *work)
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{
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struct access_report_info *info =
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container_of(work, struct access_report_info, work);
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char *target_cmd, *agent_cmd;
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target_cmd = kstrdup_quotable_cmdline(info->target, GFP_KERNEL);
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agent_cmd = kstrdup_quotable_cmdline(info->agent, GFP_KERNEL);
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pr_notice_ratelimited(
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"ptrace %s of \"%s\"[%d] was attempted by \"%s\"[%d]\n",
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info->access, target_cmd, info->target->pid, agent_cmd,
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info->agent->pid);
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kfree(agent_cmd);
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kfree(target_cmd);
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put_task_struct(info->agent);
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put_task_struct(info->target);
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kfree(info);
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}
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/* defers execution because cmdline access can sleep */
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static void report_access(const char *access, struct task_struct *target,
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struct task_struct *agent)
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{
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struct access_report_info *info;
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char agent_comm[sizeof(agent->comm)];
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assert_spin_locked(&target->alloc_lock); /* for target->comm */
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if (current->flags & PF_KTHREAD) {
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/* I don't think kthreads call task_work_run() before exiting.
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* Imagine angry ranting about procfs here.
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*/
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pr_notice_ratelimited(
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"ptrace %s of \"%s\"[%d] was attempted by \"%s\"[%d]\n",
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access, target->comm, target->pid,
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get_task_comm(agent_comm, agent), agent->pid);
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return;
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}
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info = kmalloc(sizeof(*info), GFP_ATOMIC);
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if (!info)
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return;
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init_task_work(&info->work, __report_access);
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get_task_struct(target);
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get_task_struct(agent);
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info->access = access;
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info->target = target;
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info->agent = agent;
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if (task_work_add(current, &info->work, true) == 0)
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return; /* success */
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WARN(1, "report_access called from exiting task");
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put_task_struct(target);
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put_task_struct(agent);
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kfree(info);
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}
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/**
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* yama_relation_cleanup - remove invalid entries from the relation list
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*
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*/
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static void yama_relation_cleanup(struct work_struct *work)
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{
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struct ptrace_relation *relation;
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spin_lock(&ptracer_relations_lock);
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rcu_read_lock();
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list_for_each_entry_rcu(relation, &ptracer_relations, node) {
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if (relation->invalid) {
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list_del_rcu(&relation->node);
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kfree_rcu(relation, rcu);
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}
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}
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rcu_read_unlock();
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spin_unlock(&ptracer_relations_lock);
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}
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/**
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* yama_ptracer_add - add/replace an exception for this tracer/tracee pair
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* @tracer: the task_struct of the process doing the ptrace
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* @tracee: the task_struct of the process to be ptraced
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*
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* Each tracee can have, at most, one tracer registered. Each time this
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* is called, the prior registered tracer will be replaced for the tracee.
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*
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* Returns 0 if relationship was added, -ve on error.
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*/
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static int yama_ptracer_add(struct task_struct *tracer,
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struct task_struct *tracee)
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{
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struct ptrace_relation *relation, *added;
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added = kmalloc(sizeof(*added), GFP_KERNEL);
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if (!added)
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return -ENOMEM;
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added->tracee = tracee;
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added->tracer = tracer;
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added->invalid = false;
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spin_lock(&ptracer_relations_lock);
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rcu_read_lock();
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list_for_each_entry_rcu(relation, &ptracer_relations, node) {
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if (relation->invalid)
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continue;
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if (relation->tracee == tracee) {
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list_replace_rcu(&relation->node, &added->node);
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kfree_rcu(relation, rcu);
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goto out;
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}
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}
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list_add_rcu(&added->node, &ptracer_relations);
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out:
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rcu_read_unlock();
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spin_unlock(&ptracer_relations_lock);
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return 0;
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}
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/**
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* yama_ptracer_del - remove exceptions related to the given tasks
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* @tracer: remove any relation where tracer task matches
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* @tracee: remove any relation where tracee task matches
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*/
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static void yama_ptracer_del(struct task_struct *tracer,
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struct task_struct *tracee)
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{
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struct ptrace_relation *relation;
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bool marked = false;
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rcu_read_lock();
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list_for_each_entry_rcu(relation, &ptracer_relations, node) {
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if (relation->invalid)
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continue;
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if (relation->tracee == tracee ||
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(tracer && relation->tracer == tracer)) {
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relation->invalid = true;
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marked = true;
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}
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}
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rcu_read_unlock();
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if (marked)
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schedule_work(&yama_relation_work);
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}
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/**
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* yama_task_free - check for task_pid to remove from exception list
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* @task: task being removed
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*/
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void yama_task_free(struct task_struct *task)
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{
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yama_ptracer_del(task, task);
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}
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/**
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* yama_task_prctl - check for Yama-specific prctl operations
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* @option: operation
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* @arg2: argument
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* @arg3: argument
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* @arg4: argument
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* @arg5: argument
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*
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* Return 0 on success, -ve on error. -ENOSYS is returned when Yama
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* does not handle the given option.
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*/
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int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
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unsigned long arg4, unsigned long arg5)
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{
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int rc = -ENOSYS;
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struct task_struct *myself = current;
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switch (option) {
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case PR_SET_PTRACER:
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/* Since a thread can call prctl(), find the group leader
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* before calling _add() or _del() on it, since we want
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* process-level granularity of control. The tracer group
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* leader checking is handled later when walking the ancestry
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* at the time of PTRACE_ATTACH check.
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*/
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rcu_read_lock();
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if (!thread_group_leader(myself))
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myself = rcu_dereference(myself->group_leader);
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get_task_struct(myself);
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rcu_read_unlock();
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if (arg2 == 0) {
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yama_ptracer_del(NULL, myself);
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rc = 0;
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} else if (arg2 == PR_SET_PTRACER_ANY || (int)arg2 == -1) {
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rc = yama_ptracer_add(NULL, myself);
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} else {
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struct task_struct *tracer;
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rcu_read_lock();
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tracer = find_task_by_vpid(arg2);
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if (tracer)
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get_task_struct(tracer);
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else
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rc = -EINVAL;
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rcu_read_unlock();
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if (tracer) {
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rc = yama_ptracer_add(tracer, myself);
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put_task_struct(tracer);
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}
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}
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put_task_struct(myself);
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break;
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}
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return rc;
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}
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/**
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* task_is_descendant - walk up a process family tree looking for a match
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* @parent: the process to compare against while walking up from child
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* @child: the process to start from while looking upwards for parent
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*
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* Returns 1 if child is a descendant of parent, 0 if not.
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*/
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static int task_is_descendant(struct task_struct *parent,
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struct task_struct *child)
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{
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int rc = 0;
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struct task_struct *walker = child;
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if (!parent || !child)
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return 0;
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rcu_read_lock();
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if (!thread_group_leader(parent))
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parent = rcu_dereference(parent->group_leader);
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while (walker->pid > 0) {
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if (!thread_group_leader(walker))
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walker = rcu_dereference(walker->group_leader);
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if (walker == parent) {
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rc = 1;
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break;
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}
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walker = rcu_dereference(walker->real_parent);
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}
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rcu_read_unlock();
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return rc;
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}
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/**
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* ptracer_exception_found - tracer registered as exception for this tracee
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* @tracer: the task_struct of the process attempting ptrace
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* @tracee: the task_struct of the process to be ptraced
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*
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* Returns 1 if tracer has a ptracer exception ancestor for tracee.
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*/
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static int ptracer_exception_found(struct task_struct *tracer,
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struct task_struct *tracee)
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{
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int rc = 0;
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struct ptrace_relation *relation;
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struct task_struct *parent = NULL;
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bool found = false;
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rcu_read_lock();
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/*
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* If there's already an active tracing relationship, then make an
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* exception for the sake of other accesses, like process_vm_rw().
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*/
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parent = ptrace_parent(tracee);
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if (parent != NULL && same_thread_group(parent, tracer)) {
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rc = 1;
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goto unlock;
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}
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/* Look for a PR_SET_PTRACER relationship. */
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if (!thread_group_leader(tracee))
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tracee = rcu_dereference(tracee->group_leader);
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list_for_each_entry_rcu(relation, &ptracer_relations, node) {
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if (relation->invalid)
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continue;
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if (relation->tracee == tracee) {
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parent = relation->tracer;
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found = true;
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break;
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}
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}
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if (found && (parent == NULL || task_is_descendant(parent, tracer)))
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rc = 1;
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unlock:
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rcu_read_unlock();
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return rc;
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}
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/**
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* yama_ptrace_access_check - validate PTRACE_ATTACH calls
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* @child: task that current task is attempting to ptrace
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* @mode: ptrace attach mode
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*
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* Returns 0 if following the ptrace is allowed, -ve on error.
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*/
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static int yama_ptrace_access_check(struct task_struct *child,
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unsigned int mode)
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{
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int rc = 0;
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/* require ptrace target be a child of ptracer on attach */
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if (mode & PTRACE_MODE_ATTACH) {
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switch (ptrace_scope) {
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case YAMA_SCOPE_DISABLED:
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/* No additional restrictions. */
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break;
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case YAMA_SCOPE_RELATIONAL:
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rcu_read_lock();
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if (!task_is_descendant(current, child) &&
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!ptracer_exception_found(current, child) &&
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!ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
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rc = -EPERM;
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rcu_read_unlock();
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break;
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case YAMA_SCOPE_CAPABILITY:
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rcu_read_lock();
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if (!ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
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rc = -EPERM;
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rcu_read_unlock();
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break;
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case YAMA_SCOPE_NO_ATTACH:
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default:
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rc = -EPERM;
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break;
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}
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}
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if (rc && (mode & PTRACE_MODE_NOAUDIT) == 0)
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report_access("attach", child, current);
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return rc;
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}
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/**
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* yama_ptrace_traceme - validate PTRACE_TRACEME calls
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* @parent: task that will become the ptracer of the current task
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*
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* Returns 0 if following the ptrace is allowed, -ve on error.
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*/
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int yama_ptrace_traceme(struct task_struct *parent)
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{
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int rc = 0;
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/* Only disallow PTRACE_TRACEME on more aggressive settings. */
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switch (ptrace_scope) {
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case YAMA_SCOPE_CAPABILITY:
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if (!has_ns_capability(parent, current_user_ns(), CAP_SYS_PTRACE))
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rc = -EPERM;
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break;
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case YAMA_SCOPE_NO_ATTACH:
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rc = -EPERM;
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break;
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}
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if (rc) {
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task_lock(current);
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report_access("traceme", current, parent);
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task_unlock(current);
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}
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return rc;
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}
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static struct security_hook_list yama_hooks[] = {
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LSM_HOOK_INIT(ptrace_access_check, yama_ptrace_access_check),
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LSM_HOOK_INIT(ptrace_traceme, yama_ptrace_traceme),
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LSM_HOOK_INIT(task_prctl, yama_task_prctl),
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LSM_HOOK_INIT(task_free, yama_task_free),
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};
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#ifdef CONFIG_SYSCTL
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static int yama_dointvec_minmax(struct ctl_table *table, int write,
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void __user *buffer, size_t *lenp, loff_t *ppos)
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{
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struct ctl_table table_copy;
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if (write && !capable(CAP_SYS_PTRACE))
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return -EPERM;
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/* Lock the max value if it ever gets set. */
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table_copy = *table;
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if (*(int *)table_copy.data == *(int *)table_copy.extra2)
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table_copy.extra1 = table_copy.extra2;
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return proc_dointvec_minmax(&table_copy, write, buffer, lenp, ppos);
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}
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static int zero;
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static int max_scope = YAMA_SCOPE_NO_ATTACH;
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struct ctl_path yama_sysctl_path[] = {
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{ .procname = "kernel", },
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{ .procname = "yama", },
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{ }
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};
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static struct ctl_table yama_sysctl_table[] = {
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{
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.procname = "ptrace_scope",
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.data = &ptrace_scope,
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.maxlen = sizeof(int),
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.mode = 0644,
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.proc_handler = yama_dointvec_minmax,
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.extra1 = &zero,
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.extra2 = &max_scope,
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},
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{ }
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};
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static void __init yama_init_sysctl(void)
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{
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if (!register_sysctl_paths(yama_sysctl_path, yama_sysctl_table))
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panic("Yama: sysctl registration failed.\n");
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}
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#else
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static inline void yama_init_sysctl(void) { }
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#endif /* CONFIG_SYSCTL */
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void __init yama_add_hooks(void)
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{
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pr_info("Yama: becoming mindful.\n");
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security_add_hooks(yama_hooks, ARRAY_SIZE(yama_hooks), "yama");
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yama_init_sysctl();
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}
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