Adding upstream version 4.19.249.upstream/4.19.249upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

3 files changed, 503 insertions, 0 deletions

diff --git a/security/yama/Kconfig b/security/yama/Kconfig
new file mode 100644
index 000000000..96b274055
--- /dev/null
+++ b/security/yama/Kconfig
@@ -0,0 +1,13 @@
+config SECURITY_YAMA
+	bool "Yama support"
+	depends on SECURITY
+	default n
+	help
+	  This selects Yama, which extends DAC support with additional
+	  system-wide security settings beyond regular Linux discretionary
+	  access controls. Currently available is ptrace scope restriction.
+	  Like capabilities, this security module stacks with other LSMs.
+	  Further information can be found in
+	  Documentation/admin-guide/LSM/Yama.rst.
+
+	  If you are unsure how to answer this question, answer N.
diff --git a/security/yama/Makefile b/security/yama/Makefile
new file mode 100644
index 000000000..8b5e06588
--- /dev/null
+++ b/security/yama/Makefile
@@ -0,0 +1,3 @@
+obj-$(CONFIG_SECURITY_YAMA) := yama.o
+
+yama-y := yama_lsm.o
diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
new file mode 100644
index 000000000..02514fe55
--- /dev/null
+++ b/security/yama/yama_lsm.c
@@ -0,0 +1,487 @@
+/*
+ * 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/lsm_hooks.h>
+#include <linux/sysctl.h>
+#include <linux/ptrace.h>
+#include <linux/prctl.h>
+#include <linux/ratelimit.h>
+#include <linux/workqueue.h>
+#include <linux/string_helpers.h>
+#include <linux/task_work.h>
+#include <linux/sched.h>
+#include <linux/spinlock.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);
+
+struct access_report_info {
+	struct callback_head work;
+	const char *access;
+	struct task_struct *target;
+	struct task_struct *agent;
+};
+
+static void __report_access(struct callback_head *work)
+{
+	struct access_report_info *info =
+		container_of(work, struct access_report_info, work);
+	char *target_cmd, *agent_cmd;
+
+	target_cmd = kstrdup_quotable_cmdline(info->target, GFP_KERNEL);
+	agent_cmd = kstrdup_quotable_cmdline(info->agent, GFP_KERNEL);
+
+	pr_notice_ratelimited(
+		"ptrace %s of \"%s\"[%d] was attempted by \"%s\"[%d]\n",
+		info->access, target_cmd, info->target->pid, agent_cmd,
+		info->agent->pid);
+
+	kfree(agent_cmd);
+	kfree(target_cmd);
+
+	put_task_struct(info->agent);
+	put_task_struct(info->target);
+	kfree(info);
+}
+
+/* defers execution because cmdline access can sleep */
+static void report_access(const char *access, struct task_struct *target,
+				struct task_struct *agent)
+{
+	struct access_report_info *info;
+	char agent_comm[sizeof(agent->comm)];
+
+	assert_spin_locked(&target->alloc_lock); /* for target->comm */
+
+	if (current->flags & PF_KTHREAD) {
+		/* I don't think kthreads call task_work_run() before exiting.
+		 * Imagine angry ranting about procfs here.
+		 */
+		pr_notice_ratelimited(
+		    "ptrace %s of \"%s\"[%d] was attempted by \"%s\"[%d]\n",
+		    access, target->comm, target->pid,
+		    get_task_comm(agent_comm, agent), agent->pid);
+		return;
+	}
+
+	info = kmalloc(sizeof(*info), GFP_ATOMIC);
+	if (!info)
+		return;
+	init_task_work(&info->work, __report_access);
+	get_task_struct(target);
+	get_task_struct(agent);
+	info->access = access;
+	info->target = target;
+	info->agent = agent;
+	if (task_work_add(current, &info->work, true) == 0)
+		return; /* success */
+
+	WARN(1, "report_access called from exiting task");
+	put_task_struct(target);
+	put_task_struct(agent);
+	kfree(info);
+}
+
+/**
+ * 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 = -ENOSYS;
+	struct task_struct *myself = current;
+
+	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;
+
+			tracer = find_get_task_by_vpid(arg2);
+			if (!tracer) {
+				rc = -EINVAL;
+			} else {
+				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 a 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 there's already an active tracing relationship, then make an
+	 * exception for the sake of other accesses, like process_vm_rw().
+	 */
+	parent = ptrace_parent(tracee);
+	if (parent != NULL && same_thread_group(parent, tracer)) {
+		rc = 1;
+		goto unlock;
+	}
+
+	/* Look for a PR_SET_PTRACER relationship. */
+	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;
+
+unlock:
+	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.
+ */
+static int yama_ptrace_access_check(struct task_struct *child,
+				    unsigned int mode)
+{
+	int rc = 0;
+
+	/* 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 (!pid_alive(child))
+				rc = -EPERM;
+			if (!rc && !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 && (mode & PTRACE_MODE_NOAUDIT) == 0)
+		report_access("attach", child, current);
+
+	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 = 0;
+
+	/* 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) {
+		task_lock(current);
+		report_access("traceme", current, parent);
+		task_unlock(current);
+	}
+
+	return rc;
+}
+
+static struct security_hook_list yama_hooks[] __lsm_ro_after_init = {
+	LSM_HOOK_INIT(ptrace_access_check, yama_ptrace_access_check),
+	LSM_HOOK_INIT(ptrace_traceme, yama_ptrace_traceme),
+	LSM_HOOK_INIT(task_prctl, yama_task_prctl),
+	LSM_HOOK_INIT(task_free, yama_task_free),
+};
+
+#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,
+	},
+	{ }
+};
+static void __init yama_init_sysctl(void)
+{
+	if (!register_sysctl_paths(yama_sysctl_path, yama_sysctl_table))
+		panic("Yama: sysctl registration failed.\n");
+}
+#else
+static inline void yama_init_sysctl(void) { }
+#endif /* CONFIG_SYSCTL */
+
+void __init yama_add_hooks(void)
+{
+	pr_info("Yama: becoming mindful.\n");
+	security_add_hooks(yama_hooks, ARRAY_SIZE(yama_hooks), "yama");
+	yama_init_sysctl();
+}