--- /dev/null
+/*
+ * Yama Linux Security Module
+ *
+ * Author: Kees Cook <keescook@chromium.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>
+#include <linux/workqueue.h>
+
+#define YAMA_SCOPE_DISABLED 0
+#define YAMA_SCOPE_RELATIONAL 1
+#define YAMA_SCOPE_CAPABILITY 2
+#define YAMA_SCOPE_NO_ATTACH 3
+
+static int ptrace_scope = YAMA_SCOPE_RELATIONAL;
+
+/* describe a ptrace relationship for potential exception */
+struct ptrace_relation {
+ struct task_struct *tracer;
+ struct task_struct *tracee;
+ bool invalid;
+ struct list_head node;
+ struct rcu_head rcu;
+};
+
+static LIST_HEAD(ptracer_relations);
+static DEFINE_SPINLOCK(ptracer_relations_lock);
+
+static void yama_relation_cleanup(struct work_struct *work);
+static DECLARE_WORK(yama_relation_work, yama_relation_cleanup);
+
+/**
+ * yama_relation_cleanup - remove invalid entries from the relation list
+ *
+ */
+static void yama_relation_cleanup(struct work_struct *work)
+{
+ struct ptrace_relation *relation;
+
+ spin_lock(&ptracer_relations_lock);
+ rcu_read_lock();
+ list_for_each_entry_rcu(relation, &ptracer_relations, node) {
+ if (relation->invalid) {
+ list_del_rcu(&relation->node);
+ kfree_rcu(relation, rcu);
+ }
+ }
+ rcu_read_unlock();
+ spin_unlock(&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
+ *
+ * Each tracee can have, at most, one tracer registered. Each time this
+ * is called, the prior registered tracer will be replaced for the tracee.
+ *
+ * Returns 0 if relationship was added, -ve on error.
+ */
+static int yama_ptracer_add(struct task_struct *tracer,
+ struct task_struct *tracee)
+{
+ struct ptrace_relation *relation, *added;
+
+ added = kmalloc(sizeof(*added), GFP_KERNEL);
+ if (!added)
+ return -ENOMEM;
+
+ added->tracee = tracee;
+ added->tracer = tracer;
+ added->invalid = false;
+
+ spin_lock(&ptracer_relations_lock);
+ rcu_read_lock();
+ list_for_each_entry_rcu(relation, &ptracer_relations, node) {
+ if (relation->invalid)
+ continue;
+ if (relation->tracee == tracee) {
+ list_replace_rcu(&relation->node, &added->node);
+ kfree_rcu(relation, rcu);
+ goto out;
+ }
+ }
+
+ list_add_rcu(&added->node, &ptracer_relations);
+
+out:
+ rcu_read_unlock();
+ spin_unlock(&ptracer_relations_lock);
+ return 0;
+}
+
+/**
+ * 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;
+ bool marked = false;
+
+ rcu_read_lock();
+ list_for_each_entry_rcu(relation, &ptracer_relations, node) {
+ if (relation->invalid)
+ continue;
+ if (relation->tracee == tracee ||
+ (tracer && relation->tracer == tracer)) {
+ relation->invalid = true;
+ marked = true;
+ }
+ }
+ rcu_read_unlock();
+
+ if (marked)
+ schedule_work(&yama_relation_work);
+}
+
+/**
+ * yama_task_free - check for task_pid to remove from exception list
+ * @task: task being removed
+ */
+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.
+ */
+int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
+ unsigned long arg4, unsigned long arg5)
+{
+ int rc;
+ struct task_struct *myself = current;
+
+ rc = cap_task_prctl(option, arg2, arg3, arg4, arg5);
+ if (rc != -ENOSYS)
+ return rc;
+
+ switch (option) {
+ case PR_SET_PTRACER:
+ /* Since a thread can call prctl(), find the group leader
+ * before calling _add() or _del() on it, since we want
+ * process-level granularity of control. The tracer group
+ * leader checking is handled later when walking the ancestry
+ * at the time of PTRACE_ATTACH check.
+ */
+ rcu_read_lock();
+ if (!thread_group_leader(myself))
+ myself = rcu_dereference(myself->group_leader);
+ get_task_struct(myself);
+ rcu_read_unlock();
+
+ if (arg2 == 0) {
+ yama_ptracer_del(NULL, myself);
+ rc = 0;
+ } else if (arg2 == PR_SET_PTRACER_ANY || (int)arg2 == -1) {
+ rc = yama_ptracer_add(NULL, myself);
+ } else {
+ struct task_struct *tracer;
+
+ rcu_read_lock();
+ tracer = find_task_by_vpid(arg2);
+ if (tracer)
+ get_task_struct(tracer);
+ else
+ rc = -EINVAL;
+ rcu_read_unlock();
+
+ if (tracer) {
+ rc = yama_ptracer_add(tracer, myself);
+ put_task_struct(tracer);
+ }
+ }
+
+ put_task_struct(myself);
+ break;
+ }
+
+ return rc;
+}
+
+/**
+ * task_is_descendant - walk up a process family tree looking for a match
+ * @parent: the process to compare against while walking up from child
+ * @child: the process to start from while looking upwards for parent
+ *
+ * Returns 1 if child is a descendant of parent, 0 if not.
+ */
+static int task_is_descendant(struct task_struct *parent,
+ struct task_struct *child)
+{
+ int rc = 0;
+ struct task_struct *walker = child;
+
+ if (!parent || !child)
+ return 0;
+
+ rcu_read_lock();
+ if (!thread_group_leader(parent))
+ parent = rcu_dereference(parent->group_leader);
+ while (walker->pid > 0) {
+ if (!thread_group_leader(walker))
+ walker = rcu_dereference(walker->group_leader);
+ if (walker == parent) {
+ rc = 1;
+ break;
+ }
+ walker = rcu_dereference(walker->real_parent);
+ }
+ rcu_read_unlock();
+
+ return rc;
+}
+
+/**
+ * ptracer_exception_found - tracer registered as exception for this tracee
+ * @tracer: the task_struct of the process attempting ptrace
+ * @tracee: the task_struct of the process to be ptraced
+ *
+ * Returns 1 if tracer has is ptracer exception ancestor for tracee.
+ */
+static int ptracer_exception_found(struct task_struct *tracer,
+ struct task_struct *tracee)
+{
+ int rc = 0;
+ struct ptrace_relation *relation;
+ struct task_struct *parent = NULL;
+ bool found = false;
+
+ rcu_read_lock();
+ if (!thread_group_leader(tracee))
+ tracee = rcu_dereference(tracee->group_leader);
+ list_for_each_entry_rcu(relation, &ptracer_relations, node) {
+ if (relation->invalid)
+ continue;
+ if (relation->tracee == tracee) {
+ parent = relation->tracer;
+ found = true;
+ break;
+ }
+ }
+
+ if (found && (parent == NULL || task_is_descendant(parent, tracer)))
+ rc = 1;
+ rcu_read_unlock();
+
+ return rc;
+}
+
+/**
+ * yama_ptrace_access_check - validate PTRACE_ATTACH calls
+ * @child: task that current task is attempting to ptrace
+ * @mode: ptrace attach mode
+ *
+ * Returns 0 if following the ptrace is allowed, -ve on error.
+ */
+int yama_ptrace_access_check(struct task_struct *child,
+ unsigned int mode)
+{
+ int rc;
+
+ /* If standard caps disallows it, so does Yama. We should
+ * only tighten restrictions further.
+ */
+ rc = cap_ptrace_access_check(child, mode);
+ if (rc)
+ return rc;
+
+ /* require ptrace target be a child of ptracer on attach */
+ if (mode == PTRACE_MODE_ATTACH) {
+ switch (ptrace_scope) {
+ case YAMA_SCOPE_DISABLED:
+ /* No additional restrictions. */
+ break;
+ case YAMA_SCOPE_RELATIONAL:
+ rcu_read_lock();
+ if (!task_is_descendant(current, child) &&
+ !ptracer_exception_found(current, child) &&
+ !ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
+ rc = -EPERM;
+ rcu_read_unlock();
+ break;
+ case YAMA_SCOPE_CAPABILITY:
+ rcu_read_lock();
+ if (!ns_capable(__task_cred(child)->user_ns, CAP_SYS_PTRACE))
+ rc = -EPERM;
+ rcu_read_unlock();
+ break;
+ case YAMA_SCOPE_NO_ATTACH:
+ default:
+ rc = -EPERM;
+ break;
+ }
+ }
+
+ if (rc) {
+ printk_ratelimited(KERN_NOTICE
+ "ptrace of pid %d was attempted by: %s (pid %d)\n",
+ child->pid, current->comm, current->pid);
+ }
+
+ return rc;
+}
+
+/**
+ * yama_ptrace_traceme - validate PTRACE_TRACEME calls
+ * @parent: task that will become the ptracer of the current task
+ *
+ * Returns 0 if following the ptrace is allowed, -ve on error.
+ */
+int yama_ptrace_traceme(struct task_struct *parent)
+{
+ int rc;
+
+ /* If standard caps disallows it, so does Yama. We should
+ * only tighten restrictions further.
+ */
+ rc = cap_ptrace_traceme(parent);
+ if (rc)
+ return rc;
+
+ /* Only disallow PTRACE_TRACEME on more aggressive settings. */
+ switch (ptrace_scope) {
+ case YAMA_SCOPE_CAPABILITY:
+ if (!has_ns_capability(parent, current_user_ns(), CAP_SYS_PTRACE))
+ rc = -EPERM;
+ break;
+ case YAMA_SCOPE_NO_ATTACH:
+ rc = -EPERM;
+ break;
+ }
+
+ if (rc) {
+ printk_ratelimited(KERN_NOTICE
+ "ptraceme of pid %d was attempted by: %s (pid %d)\n",
+ current->pid, parent->comm, parent->pid);
+ }
+
+ return rc;
+}
+
+#ifndef CONFIG_SECURITY_YAMA_STACKED
+static struct security_operations yama_ops = {
+ .name = "yama",
+
+ .ptrace_access_check = yama_ptrace_access_check,
+ .ptrace_traceme = yama_ptrace_traceme,
+ .task_prctl = yama_task_prctl,
+ .task_free = yama_task_free,
+};
+#endif
+
+#ifdef CONFIG_SYSCTL
+static int yama_dointvec_minmax(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+ struct ctl_table table_copy;
+
+ if (write && !capable(CAP_SYS_PTRACE))
+ return -EPERM;
+
+ /* Lock the max value if it ever gets set. */
+ table_copy = *table;
+ if (*(int *)table_copy.data == *(int *)table_copy.extra2)
+ table_copy.extra1 = table_copy.extra2;
+
+ return proc_dointvec_minmax(&table_copy, write, buffer, lenp, ppos);
+}
+
+static int zero;
+static int max_scope = YAMA_SCOPE_NO_ATTACH;
+
+struct ctl_path yama_sysctl_path[] = {
+ { .procname = "kernel", },
+ { .procname = "yama", },
+ { }
+};
+
+static struct ctl_table yama_sysctl_table[] = {
+ {
+ .procname = "ptrace_scope",
+ .data = &ptrace_scope,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = yama_dointvec_minmax,
+ .extra1 = &zero,
+ .extra2 = &max_scope,
+ },
+ { }
+};
+#endif /* CONFIG_SYSCTL */
+
+static __init int yama_init(void)
+{
+#ifndef CONFIG_SECURITY_YAMA_STACKED
+ if (!security_module_enable(&yama_ops))
+ return 0;
+#endif
+
+ printk(KERN_INFO "Yama: becoming mindful.\n");
+
+#ifndef CONFIG_SECURITY_YAMA_STACKED
+ if (register_security(&yama_ops))
+ panic("Yama: kernel registration failed.\n");
+#endif
+
+#ifdef CONFIG_SYSCTL
+ if (!register_sysctl_paths(yama_sysctl_path, yama_sysctl_table))
+ panic("Yama: sysctl registration failed.\n");
+#endif
+
+ return 0;
+}
+
+security_initcall(yama_init);
Code Review / kvmfornfv.git / blobdiff