/*
 * 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 (!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();
}