![Kees Cook](/assets/img/avatar_default.png)
Now that minor LSMs can cleanly stack with major LSMs, remove the unneeded config for Yama to be made to explicitly stack. Just selecting the main Yama CONFIG will allow it to work, regardless of the major LSM. Since distros using Yama are already forcing it to stack, this is effectively a no-op change. Additionally add MAINTAINERS entry. Signed-off-by: Kees Cook <keescook@chromium.org> Signed-off-by: James Morris <james.l.morris@oracle.com>
409 lines
10 KiB
C
409 lines
10 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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#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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/**
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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 is 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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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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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) {
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printk_ratelimited(KERN_NOTICE
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"ptrace of pid %d was attempted by: %s (pid %d)\n",
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child->pid, current->comm, current->pid);
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}
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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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printk_ratelimited(KERN_NOTICE
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"ptraceme of pid %d was attempted by: %s (pid %d)\n",
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current->pid, parent->comm, parent->pid);
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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));
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yama_init_sysctl();
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}
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