--- /dev/null
+Yama is a Linux Security Module that collects a number of system-wide DAC
+security protections that are not handled by the core kernel itself. To
+select it at boot time, specify "security=yama" (though this will disable
+any other LSM).
+
+Yama is controlled through sysctl in /proc/sys/kernel/yama:
+
+- ptrace_scope
+
+==============================================================
+
+ptrace_scope:
+
+As Linux grows in popularity, it will become a larger target for
+malware. One particularly troubling weakness of the Linux process
+interfaces is that a single user is able to examine the memory and
+running state of any of their processes. For example, if one application
+(e.g. Pidgin) was compromised, it would be possible for an attacker to
+attach to other running processes (e.g. Firefox, SSH sessions, GPG agent,
+etc) to extract additional credentials and continue to expand the scope
+of their attack without resorting to user-assisted phishing.
+
+This is not a theoretical problem. SSH session hijacking
+(http://www.storm.net.nz/projects/7) and arbitrary code injection
+(http://c-skills.blogspot.com/2007/05/injectso.html) attacks already
+exist and remain possible if ptrace is allowed to operate as before.
+Since ptrace is not commonly used by non-developers and non-admins, system
+builders should be allowed the option to disable this debugging system.
+
+For a solution, some applications use prctl(PR_SET_DUMPABLE, ...) to
+specifically disallow such ptrace attachment (e.g. ssh-agent), but many
+do not. A more general solution is to only allow ptrace directly from a
+parent to a child process (i.e. direct "gdb EXE" and "strace EXE" still
+work), or with CAP_SYS_PTRACE (i.e. "gdb --pid=PID", and "strace -p PID"
+still work as root).
+
+For software that has defined application-specific relationships
+between a debugging process and its inferior (crash handlers, etc),
+prctl(PR_SET_PTRACER, pid, ...) can be used. An inferior can declare which
+other process (and its descendents) are allowed to call PTRACE_ATTACH
+against it. Only one such declared debugging process can exists for
+each inferior at a time. For example, this is used by KDE, Chromium, and
+Firefox's crash handlers, and by Wine for allowing only Wine processes
+to ptrace each other.
+
+0 - classic ptrace permissions: a process can PTRACE_ATTACH to any other
+ process running under the same uid, as long as it is dumpable (i.e.
+ did not transition uids, start privileged, or have called
+ prctl(PR_SET_DUMPABLE...) already).
+
+1 - restricted ptrace: a process must have a predefined relationship
+ with the inferior it wants to call PTRACE_ATTACH on. By default,
+ this relationship is that of only its descendants when the above
+ classic criteria is also met. To change the relationship, an
+ inferior can call prctl(PR_SET_PTRACER, debugger, ...) to declare
+ an allowed debugger PID to call PTRACE_ATTACH on the inferior.
+
+The original children-only logic was based on the restrictions in grsecurity.
+
+==============================================================
--- /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>
+
+static int ptrace_scope = 1;
+
+/* describe a ptrace relationship for potential exception */
+struct ptrace_relation {
+ struct task_struct *tracer;
+ struct task_struct *tracee;
+ struct list_head node;
+};
+
+static LIST_HEAD(ptracer_relations);
+static DEFINE_SPINLOCK(ptracer_relations_lock);
+
+/**
+ * yama_ptracer_add - add/replace an exception for this tracer/tracee pair
+ * @tracer: the task_struct of the process doing the ptrace
+ * @tracee: the task_struct of the process to be ptraced
+ *
+ * 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)
+{
+ int rc = 0;
+ struct ptrace_relation *added;
+ struct ptrace_relation *entry, *relation = NULL;
+
+ added = kmalloc(sizeof(*added), GFP_KERNEL);
+ if (!added)
+ return -ENOMEM;
+
+ spin_lock_bh(&ptracer_relations_lock);
+ list_for_each_entry(entry, &ptracer_relations, node)
+ if (entry->tracee == tracee) {
+ relation = entry;
+ break;
+ }
+ if (!relation) {
+ relation = added;
+ relation->tracee = tracee;
+ list_add(&relation->node, &ptracer_relations);
+ }
+ relation->tracer = tracer;
+
+ spin_unlock_bh(&ptracer_relations_lock);
+ if (added != relation)
+ kfree(added);
+
+ return rc;
+}
+
+/**
+ * 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, *safe;
+
+ spin_lock_bh(&ptracer_relations_lock);
+ list_for_each_entry_safe(relation, safe, &ptracer_relations, node)
+ if (relation->tracee == tracee ||
+ relation->tracer == tracer) {
+ list_del(&relation->node);
+ kfree(relation);
+ }
+ spin_unlock_bh(&ptracer_relations_lock);
+}
+
+/**
+ * yama_task_free - check for task_pid to remove from exception list
+ * @task: task being removed
+ */
+static void yama_task_free(struct task_struct *task)
+{
+ yama_ptracer_del(task, task);
+}
+
+/**
+ * yama_task_prctl - check for Yama-specific prctl operations
+ * @option: operation
+ * @arg2: argument
+ * @arg3: argument
+ * @arg4: argument
+ * @arg5: argument
+ *
+ * Return 0 on success, -ve on error. -ENOSYS is returned when Yama
+ * does not handle the given option.
+ */
+static 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 {
+ 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;
+
+ spin_lock_bh(&ptracer_relations_lock);
+ rcu_read_lock();
+ if (!thread_group_leader(tracee))
+ tracee = rcu_dereference(tracee->group_leader);
+ list_for_each_entry(relation, &ptracer_relations, node)
+ if (relation->tracee == tracee) {
+ parent = relation->tracer;
+ break;
+ }
+
+ if (task_is_descendant(parent, tracer))
+ rc = 1;
+ rcu_read_unlock();
+ spin_unlock_bh(&ptracer_relations_lock);
+
+ 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.
+ */
+static 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 &&
+ ptrace_scope &&
+ !task_is_descendant(current, child) &&
+ !ptracer_exception_found(current, child) &&
+ !capable(CAP_SYS_PTRACE))
+ rc = -EPERM;
+
+ if (rc) {
+ char name[sizeof(current->comm)];
+ printk_ratelimited(KERN_NOTICE "ptrace of non-child"
+ " pid %d was attempted by: %s (pid %d)\n",
+ child->pid,
+ get_task_comm(name, current),
+ current->pid);
+ }
+
+ return rc;
+}
+
+static struct security_operations yama_ops = {
+ .name = "yama",
+
+ .ptrace_access_check = yama_ptrace_access_check,
+ .task_prctl = yama_task_prctl,
+ .task_free = yama_task_free,
+};
+
+#ifdef CONFIG_SYSCTL
+static int zero;
+static int one = 1;
+
+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 = proc_dointvec_minmax,
+ .extra1 = &zero,
+ .extra2 = &one,
+ },
+ { }
+};
+#endif /* CONFIG_SYSCTL */
+
+static __init int yama_init(void)
+{
+ if (!security_module_enable(&yama_ops))
+ return 0;
+
+ printk(KERN_INFO "Yama: becoming mindful.\n");
+
+ if (register_security(&yama_ops))
+ panic("Yama: kernel registration failed.\n");
+
+#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);
projects / GitHub / exynos8895 / android_kernel_samsung_universal8895.git / commitdiff