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@@ -0,0 +1,323 @@
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+/*
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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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+
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+#include <linux/security.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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+
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+static int ptrace_scope = 1;
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+
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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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+ struct list_head node;
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+};
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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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+
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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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+ int rc = 0;
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+ struct ptrace_relation *added;
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+ struct ptrace_relation *entry, *relation = NULL;
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+
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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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+
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+ spin_lock_bh(&ptracer_relations_lock);
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+ list_for_each_entry(entry, &ptracer_relations, node)
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+ if (entry->tracee == tracee) {
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+ relation = entry;
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+ break;
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+ }
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+ if (!relation) {
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+ relation = added;
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+ relation->tracee = tracee;
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+ list_add(&relation->node, &ptracer_relations);
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+ }
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+ relation->tracer = tracer;
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+
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+ spin_unlock_bh(&ptracer_relations_lock);
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+ if (added != relation)
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+ kfree(added);
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+
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+ return rc;
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+}
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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, *safe;
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+
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+ spin_lock_bh(&ptracer_relations_lock);
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+ list_for_each_entry_safe(relation, safe, &ptracer_relations, node)
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+ if (relation->tracee == tracee ||
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+ (tracer && relation->tracer == tracer)) {
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+ list_del(&relation->node);
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+ kfree(relation);
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+ }
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+ spin_unlock_bh(&ptracer_relations_lock);
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+}
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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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+static 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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+/**
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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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+static 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;
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+ struct task_struct *myself = current;
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+
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+ rc = cap_task_prctl(option, arg2, arg3, arg4, arg5);
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+ if (rc != -ENOSYS)
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+ return rc;
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+
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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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+
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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) {
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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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+
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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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+
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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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+
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+ put_task_struct(myself);
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+ break;
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+ }
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+
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+ return rc;
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+}
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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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+
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+ if (!parent || !child)
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+ return 0;
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+
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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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+
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+ return rc;
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+}
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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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+
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+ spin_lock_bh(&ptracer_relations_lock);
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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(relation, &ptracer_relations, node)
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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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+ spin_unlock_bh(&ptracer_relations_lock);
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+
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+ return rc;
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+}
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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;
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+
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+ /* If standard caps disallows it, so does Yama. We should
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+ * only tighten restrictions further.
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+ */
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+ rc = cap_ptrace_access_check(child, mode);
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+ if (rc)
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+ return rc;
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+
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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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+ ptrace_scope &&
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+ !task_is_descendant(current, child) &&
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+ !ptracer_exception_found(current, child) &&
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+ !capable(CAP_SYS_PTRACE))
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+ rc = -EPERM;
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+
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+ if (rc) {
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+ char name[sizeof(current->comm)];
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+ printk_ratelimited(KERN_NOTICE "ptrace of non-child"
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+ " pid %d was attempted by: %s (pid %d)\n",
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+ child->pid,
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+ get_task_comm(name, current),
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+ current->pid);
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+ }
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+
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+ return rc;
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+}
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+
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+static struct security_operations yama_ops = {
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+ .name = "yama",
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+
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+ .ptrace_access_check = yama_ptrace_access_check,
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+ .task_prctl = yama_task_prctl,
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+ .task_free = yama_task_free,
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+};
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+
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+#ifdef CONFIG_SYSCTL
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+static int zero;
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+static int one = 1;
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+
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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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+
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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 = proc_dointvec_minmax,
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+ .extra1 = &zero,
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+ .extra2 = &one,
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+ },
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+ { }
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+};
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+#endif /* CONFIG_SYSCTL */
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+
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+static __init int yama_init(void)
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+{
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+ if (!security_module_enable(&yama_ops))
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+ return 0;
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+
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+ printk(KERN_INFO "Yama: becoming mindful.\n");
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+
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+ if (register_security(&yama_ops))
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+ panic("Yama: kernel registration failed.\n");
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+
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+#ifdef CONFIG_SYSCTL
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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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+#endif
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+
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+ return 0;
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+}
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+
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+security_initcall(yama_init);
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