Fixed MTP to work with TWRP

security/yama/yama_lsm.c

@@ -0,0 +1,443 @@
+/*
+ * 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)
+{
+	int rc;
+
+	if (write && !capable(CAP_SYS_PTRACE))
+		return -EPERM;
+
+	rc = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+	if (rc)
+		return rc;
+
+	/* Lock the max value if it ever gets set. */
+	if (write && *(int *)table->data == *(int *)table->extra2)
+		table->extra1 = table->extra2;
+
+	return rc;
+}
+
+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);