Merge branch 'drm-next-3.9' of git://people.freedesktop.org/~agd5f/linux into drm...

[linux-2.6/libata-dev.git] / kernel / ptrace.c

/*
 * linux/kernel/ptrace.c
 *
 * (C) Copyright 1999 Linus Torvalds
 *
 * Common interfaces for "ptrace()" which we do not want
 * to continually duplicate across every architecture.
 */

#include <linux/capability.h>
#include <linux/export.h>
#include <linux/sched.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/ptrace.h>
#include <linux/security.h>
#include <linux/signal.h>
#include <linux/audit.h>
#include <linux/pid_namespace.h>
#include <linux/syscalls.h>
#include <linux/uaccess.h>
#include <linux/regset.h>
#include <linux/hw_breakpoint.h>
#include <linux/cn_proc.h>


static int ptrace_trapping_sleep_fn(void *flags)
{
        schedule();
        return 0;
}

/*
 * ptrace a task: make the debugger its new parent and
 * move it to the ptrace list.
 *
 * Must be called with the tasklist lock write-held.
 */
void __ptrace_link(struct task_struct *child, struct task_struct *new_parent)
{
        BUG_ON(!list_empty(&child->ptrace_entry));
        list_add(&child->ptrace_entry, &new_parent->ptraced);
        child->parent = new_parent;
}

/**
 * __ptrace_unlink - unlink ptracee and restore its execution state
 * @child: ptracee to be unlinked
 *
 * Remove @child from the ptrace list, move it back to the original parent,
 * and restore the execution state so that it conforms to the group stop
 * state.
 *
 * Unlinking can happen via two paths - explicit PTRACE_DETACH or ptracer
 * exiting.  For PTRACE_DETACH, unless the ptracee has been killed between
 * ptrace_check_attach() and here, it's guaranteed to be in TASK_TRACED.
 * If the ptracer is exiting, the ptracee can be in any state.
 *
 * After detach, the ptracee should be in a state which conforms to the
 * group stop.  If the group is stopped or in the process of stopping, the
 * ptracee should be put into TASK_STOPPED; otherwise, it should be woken
 * up from TASK_TRACED.
 *
 * If the ptracee is in TASK_TRACED and needs to be moved to TASK_STOPPED,
 * it goes through TRACED -> RUNNING -> STOPPED transition which is similar
 * to but in the opposite direction of what happens while attaching to a
 * stopped task.  However, in this direction, the intermediate RUNNING
 * state is not hidden even from the current ptracer and if it immediately
 * re-attaches and performs a WNOHANG wait(2), it may fail.
 *
 * CONTEXT:
 * write_lock_irq(tasklist_lock)
 */
void __ptrace_unlink(struct task_struct *child)
{
        BUG_ON(!child->ptrace);

        child->ptrace = 0;
        child->parent = child->real_parent;
        list_del_init(&child->ptrace_entry);

        spin_lock(&child->sighand->siglock);

        /*
         * Clear all pending traps and TRAPPING.  TRAPPING should be
         * cleared regardless of JOBCTL_STOP_PENDING.  Do it explicitly.
         */
        task_clear_jobctl_pending(child, JOBCTL_TRAP_MASK);
        task_clear_jobctl_trapping(child);

        /*
         * Reinstate JOBCTL_STOP_PENDING if group stop is in effect and
         * @child isn't dead.
         */
        if (!(child->flags & PF_EXITING) &&
            (child->signal->flags & SIGNAL_STOP_STOPPED ||
             child->signal->group_stop_count)) {
                child->jobctl |= JOBCTL_STOP_PENDING;

                /*
                 * This is only possible if this thread was cloned by the
                 * traced task running in the stopped group, set the signal
                 * for the future reports.
                 * FIXME: we should change ptrace_init_task() to handle this
                 * case.
                 */
                if (!(child->jobctl & JOBCTL_STOP_SIGMASK))
                        child->jobctl |= SIGSTOP;
        }

        /*
         * If transition to TASK_STOPPED is pending or in TASK_TRACED, kick
         * @child in the butt.  Note that @resume should be used iff @child
         * is in TASK_TRACED; otherwise, we might unduly disrupt
         * TASK_KILLABLE sleeps.
         */
        if (child->jobctl & JOBCTL_STOP_PENDING || task_is_traced(child))
                ptrace_signal_wake_up(child, true);

        spin_unlock(&child->sighand->siglock);
}

/* Ensure that nothing can wake it up, even SIGKILL */
static bool ptrace_freeze_traced(struct task_struct *task)
{
        bool ret = false;

        /* Lockless, nobody but us can set this flag */
        if (task->jobctl & JOBCTL_LISTENING)
                return ret;

        spin_lock_irq(&task->sighand->siglock);
        if (task_is_traced(task) && !__fatal_signal_pending(task)) {
                task->state = __TASK_TRACED;
                ret = true;
        }
        spin_unlock_irq(&task->sighand->siglock);

        return ret;
}

static void ptrace_unfreeze_traced(struct task_struct *task)
{
        if (task->state != __TASK_TRACED)
                return;

        WARN_ON(!task->ptrace || task->parent != current);

        spin_lock_irq(&task->sighand->siglock);
        if (__fatal_signal_pending(task))
                wake_up_state(task, __TASK_TRACED);
        else
                task->state = TASK_TRACED;
        spin_unlock_irq(&task->sighand->siglock);
}

/**
 * ptrace_check_attach - check whether ptracee is ready for ptrace operation
 * @child: ptracee to check for
 * @ignore_state: don't check whether @child is currently %TASK_TRACED
 *
 * Check whether @child is being ptraced by %current and ready for further
 * ptrace operations.  If @ignore_state is %false, @child also should be in
 * %TASK_TRACED state and on return the child is guaranteed to be traced
 * and not executing.  If @ignore_state is %true, @child can be in any
 * state.
 *
 * CONTEXT:
 * Grabs and releases tasklist_lock and @child->sighand->siglock.
 *
 * RETURNS:
 * 0 on success, -ESRCH if %child is not ready.
 */
static int ptrace_check_attach(struct task_struct *child, bool ignore_state)
{
        int ret = -ESRCH;

        /*
         * We take the read lock around doing both checks to close a
         * possible race where someone else was tracing our child and
         * detached between these two checks.  After this locked check,
         * we are sure that this is our traced child and that can only
         * be changed by us so it's not changing right after this.
         */
        read_lock(&tasklist_lock);
        if (child->ptrace && child->parent == current) {
                WARN_ON(child->state == __TASK_TRACED);
                /*
                 * child->sighand can't be NULL, release_task()
                 * does ptrace_unlink() before __exit_signal().
                 */
                if (ignore_state || ptrace_freeze_traced(child))
                        ret = 0;
        }
        read_unlock(&tasklist_lock);

        if (!ret && !ignore_state) {
                if (!wait_task_inactive(child, __TASK_TRACED)) {
                        /*
                         * This can only happen if may_ptrace_stop() fails and
                         * ptrace_stop() changes ->state back to TASK_RUNNING,
                         * so we should not worry about leaking __TASK_TRACED.
                         */
                        WARN_ON(child->state == __TASK_TRACED);
                        ret = -ESRCH;
                }
        }

        return ret;
}

static int ptrace_has_cap(struct user_namespace *ns, unsigned int mode)
{
        if (mode & PTRACE_MODE_NOAUDIT)
                return has_ns_capability_noaudit(current, ns, CAP_SYS_PTRACE);
        else
                return has_ns_capability(current, ns, CAP_SYS_PTRACE);
}

/* Returns 0 on success, -errno on denial. */
static int __ptrace_may_access(struct task_struct *task, unsigned int mode)
{
        const struct cred *cred = current_cred(), *tcred;

        /* May we inspect the given task?
         * This check is used both for attaching with ptrace
         * and for allowing access to sensitive information in /proc.
         *
         * ptrace_attach denies several cases that /proc allows
         * because setting up the necessary parent/child relationship
         * or halting the specified task is impossible.
         */
        int dumpable = 0;
        /* Don't let security modules deny introspection */
        if (task == current)
                return 0;
        rcu_read_lock();
        tcred = __task_cred(task);
        if (uid_eq(cred->uid, tcred->euid) &&
            uid_eq(cred->uid, tcred->suid) &&
            uid_eq(cred->uid, tcred->uid)  &&
            gid_eq(cred->gid, tcred->egid) &&
            gid_eq(cred->gid, tcred->sgid) &&
            gid_eq(cred->gid, tcred->gid))
                goto ok;
        if (ptrace_has_cap(tcred->user_ns, mode))
                goto ok;
        rcu_read_unlock();
        return -EPERM;
ok:
        rcu_read_unlock();
        smp_rmb();
        if (task->mm)
                dumpable = get_dumpable(task->mm);
        rcu_read_lock();
        if (!dumpable && !ptrace_has_cap(__task_cred(task)->user_ns, mode)) {
                rcu_read_unlock();
                return -EPERM;
        }
        rcu_read_unlock();

        return security_ptrace_access_check(task, mode);
}

bool ptrace_may_access(struct task_struct *task, unsigned int mode)
{
        int err;
        task_lock(task);
        err = __ptrace_may_access(task, mode);
        task_unlock(task);
        return !err;
}

static int ptrace_attach(struct task_struct *task, long request,
                         unsigned long addr,
                         unsigned long flags)
{
        bool seize = (request == PTRACE_SEIZE);
        int retval;

        retval = -EIO;
        if (seize) {
                if (addr != 0)
                        goto out;
                if (flags & ~(unsigned long)PTRACE_O_MASK)
                        goto out;
                flags = PT_PTRACED | PT_SEIZED | (flags << PT_OPT_FLAG_SHIFT);
        } else {
                flags = PT_PTRACED;
        }

        audit_ptrace(task);

        retval = -EPERM;
        if (unlikely(task->flags & PF_KTHREAD))
                goto out;
        if (same_thread_group(task, current))
                goto out;

        /*
         * Protect exec's credential calculations against our interference;
         * SUID, SGID and LSM creds get determined differently
         * under ptrace.
         */
        retval = -ERESTARTNOINTR;
        if (mutex_lock_interruptible(&task->signal->cred_guard_mutex))
                goto out;

        task_lock(task);
        retval = __ptrace_may_access(task, PTRACE_MODE_ATTACH);
        task_unlock(task);
        if (retval)
                goto unlock_creds;

        write_lock_irq(&tasklist_lock);
        retval = -EPERM;
        if (unlikely(task->exit_state))
                goto unlock_tasklist;
        if (task->ptrace)
                goto unlock_tasklist;

        if (seize)
                flags |= PT_SEIZED;
        rcu_read_lock();
        if (ns_capable(__task_cred(task)->user_ns, CAP_SYS_PTRACE))
                flags |= PT_PTRACE_CAP;
        rcu_read_unlock();
        task->ptrace = flags;

        __ptrace_link(task, current);

        /* SEIZE doesn't trap tracee on attach */
        if (!seize)
                send_sig_info(SIGSTOP, SEND_SIG_FORCED, task);

        spin_lock(&task->sighand->siglock);

        /*
         * If the task is already STOPPED, set JOBCTL_TRAP_STOP and
         * TRAPPING, and kick it so that it transits to TRACED.  TRAPPING
         * will be cleared if the child completes the transition or any
         * event which clears the group stop states happens.  We'll wait
         * for the transition to complete before returning from this
         * function.
         *
         * This hides STOPPED -> RUNNING -> TRACED transition from the
         * attaching thread but a different thread in the same group can
         * still observe the transient RUNNING state.  IOW, if another
         * thread's WNOHANG wait(2) on the stopped tracee races against
         * ATTACH, the wait(2) may fail due to the transient RUNNING.
         *
         * The following task_is_stopped() test is safe as both transitions
         * in and out of STOPPED are protected by siglock.
         */
        if (task_is_stopped(task) &&
            task_set_jobctl_pending(task, JOBCTL_TRAP_STOP | JOBCTL_TRAPPING))
                signal_wake_up_state(task, __TASK_STOPPED);

        spin_unlock(&task->sighand->siglock);

        retval = 0;
unlock_tasklist:
        write_unlock_irq(&tasklist_lock);
unlock_creds:
        mutex_unlock(&task->signal->cred_guard_mutex);
out:
        if (!retval) {
                wait_on_bit(&task->jobctl, JOBCTL_TRAPPING_BIT,
                            ptrace_trapping_sleep_fn, TASK_UNINTERRUPTIBLE);
                proc_ptrace_connector(task, PTRACE_ATTACH);
        }

        return retval;
}

/**
 * ptrace_traceme  --  helper for PTRACE_TRACEME
 *
 * Performs checks and sets PT_PTRACED.
 * Should be used by all ptrace implementations for PTRACE_TRACEME.
 */
static int ptrace_traceme(void)
{
        int ret = -EPERM;

        write_lock_irq(&tasklist_lock);
        /* Are we already being traced? */
        if (!current->ptrace) {
                ret = security_ptrace_traceme(current->parent);
                /*
                 * Check PF_EXITING to ensure ->real_parent has not passed
                 * exit_ptrace(). Otherwise we don't report the error but
                 * pretend ->real_parent untraces us right after return.
                 */
                if (!ret && !(current->real_parent->flags & PF_EXITING)) {
                        current->ptrace = PT_PTRACED;
                        __ptrace_link(current, current->real_parent);
                }
        }
        write_unlock_irq(&tasklist_lock);

        return ret;
}

/*
 * Called with irqs disabled, returns true if childs should reap themselves.
 */
static int ignoring_children(struct sighand_struct *sigh)
{
        int ret;
        spin_lock(&sigh->siglock);
        ret = (sigh->action[SIGCHLD-1].sa.sa_handler == SIG_IGN) ||
              (sigh->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT);
        spin_unlock(&sigh->siglock);
        return ret;
}

/*
 * Called with tasklist_lock held for writing.
 * Unlink a traced task, and clean it up if it was a traced zombie.
 * Return true if it needs to be reaped with release_task().
 * (We can't call release_task() here because we already hold tasklist_lock.)
 *
 * If it's a zombie, our attachedness prevented normal parent notification
 * or self-reaping.  Do notification now if it would have happened earlier.
 * If it should reap itself, return true.
 *
 * If it's our own child, there is no notification to do. But if our normal
 * children self-reap, then this child was prevented by ptrace and we must
 * reap it now, in that case we must also wake up sub-threads sleeping in
 * do_wait().
 */
static bool __ptrace_detach(struct task_struct *tracer, struct task_struct *p)
{
        bool dead;

        __ptrace_unlink(p);

        if (p->exit_state != EXIT_ZOMBIE)
                return false;

        dead = !thread_group_leader(p);

        if (!dead && thread_group_empty(p)) {
                if (!same_thread_group(p->real_parent, tracer))
                        dead = do_notify_parent(p, p->exit_signal);
                else if (ignoring_children(tracer->sighand)) {
                        __wake_up_parent(p, tracer);
                        dead = true;
                }
        }
        /* Mark it as in the process of being reaped. */
        if (dead)
                p->exit_state = EXIT_DEAD;
        return dead;
}

static int ptrace_detach(struct task_struct *child, unsigned int data)
{
        bool dead = false;

        if (!valid_signal(data))
                return -EIO;

        /* Architecture-specific hardware disable .. */
        ptrace_disable(child);
        clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);

        write_lock_irq(&tasklist_lock);
        /*
         * This child can be already killed. Make sure de_thread() or
         * our sub-thread doing do_wait() didn't do release_task() yet.
         */
        if (child->ptrace) {
                child->exit_code = data;
                dead = __ptrace_detach(current, child);
        }
        write_unlock_irq(&tasklist_lock);

        proc_ptrace_connector(child, PTRACE_DETACH);
        if (unlikely(dead))
                release_task(child);

        return 0;
}

/*
 * Detach all tasks we were using ptrace on. Called with tasklist held
 * for writing, and returns with it held too. But note it can release
 * and reacquire the lock.
 */
void exit_ptrace(struct task_struct *tracer)
        __releases(&tasklist_lock)
        __acquires(&tasklist_lock)
{
        struct task_struct *p, *n;
        LIST_HEAD(ptrace_dead);

        if (likely(list_empty(&tracer->ptraced)))
                return;

        list_for_each_entry_safe(p, n, &tracer->ptraced, ptrace_entry) {
                if (unlikely(p->ptrace & PT_EXITKILL))
                        send_sig_info(SIGKILL, SEND_SIG_FORCED, p);

                if (__ptrace_detach(tracer, p))
                        list_add(&p->ptrace_entry, &ptrace_dead);
        }

        write_unlock_irq(&tasklist_lock);
        BUG_ON(!list_empty(&tracer->ptraced));

        list_for_each_entry_safe(p, n, &ptrace_dead, ptrace_entry) {
                list_del_init(&p->ptrace_entry);
                release_task(p);
        }

        write_lock_irq(&tasklist_lock);
}

int ptrace_readdata(struct task_struct *tsk, unsigned long src, char __user *dst, int len)
{
        int copied = 0;

        while (len > 0) {
                char buf[128];
                int this_len, retval;

                this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
                retval = access_process_vm(tsk, src, buf, this_len, 0);
                if (!retval) {
                        if (copied)
                                break;
                        return -EIO;
                }
                if (copy_to_user(dst, buf, retval))
                        return -EFAULT;
                copied += retval;
                src += retval;
                dst += retval;
                len -= retval;
        }
        return copied;
}

int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned long dst, int len)
{
        int copied = 0;

        while (len > 0) {
                char buf[128];
                int this_len, retval;

                this_len = (len > sizeof(buf)) ? sizeof(buf) : len;
                if (copy_from_user(buf, src, this_len))
                        return -EFAULT;
                retval = access_process_vm(tsk, dst, buf, this_len, 1);
                if (!retval) {
                        if (copied)
                                break;
                        return -EIO;
                }
                copied += retval;
                src += retval;
                dst += retval;
                len -= retval;
        }
        return copied;
}

static int ptrace_setoptions(struct task_struct *child, unsigned long data)
{
        unsigned flags;

        if (data & ~(unsigned long)PTRACE_O_MASK)
                return -EINVAL;

        /* Avoid intermediate state when all opts are cleared */
        flags = child->ptrace;
        flags &= ~(PTRACE_O_MASK << PT_OPT_FLAG_SHIFT);
        flags |= (data << PT_OPT_FLAG_SHIFT);
        child->ptrace = flags;

        return 0;
}

static int ptrace_getsiginfo(struct task_struct *child, siginfo_t *info)
{
        unsigned long flags;
        int error = -ESRCH;

        if (lock_task_sighand(child, &flags)) {
                error = -EINVAL;
                if (likely(child->last_siginfo != NULL)) {
                        *info = *child->last_siginfo;
                        error = 0;
                }
                unlock_task_sighand(child, &flags);
        }
        return error;
}

static int ptrace_setsiginfo(struct task_struct *child, const siginfo_t *info)
{
        unsigned long flags;
        int error = -ESRCH;

        if (lock_task_sighand(child, &flags)) {
                error = -EINVAL;
                if (likely(child->last_siginfo != NULL)) {
                        *child->last_siginfo = *info;
                        error = 0;
                }
                unlock_task_sighand(child, &flags);
        }
        return error;
}


#ifdef PTRACE_SINGLESTEP
#define is_singlestep(request)          ((request) == PTRACE_SINGLESTEP)
#else
#define is_singlestep(request)          0
#endif

#ifdef PTRACE_SINGLEBLOCK
#define is_singleblock(request)         ((request) == PTRACE_SINGLEBLOCK)
#else
#define is_singleblock(request)         0
#endif

#ifdef PTRACE_SYSEMU
#define is_sysemu_singlestep(request)   ((request) == PTRACE_SYSEMU_SINGLESTEP)
#else
#define is_sysemu_singlestep(request)   0
#endif

static int ptrace_resume(struct task_struct *child, long request,
                         unsigned long data)
{
        if (!valid_signal(data))
                return -EIO;

        if (request == PTRACE_SYSCALL)
                set_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
        else
                clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);

#ifdef TIF_SYSCALL_EMU
        if (request == PTRACE_SYSEMU || request == PTRACE_SYSEMU_SINGLESTEP)
                set_tsk_thread_flag(child, TIF_SYSCALL_EMU);
        else
                clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
#endif

        if (is_singleblock(request)) {
                if (unlikely(!arch_has_block_step()))
                        return -EIO;
                user_enable_block_step(child);
        } else if (is_singlestep(request) || is_sysemu_singlestep(request)) {
                if (unlikely(!arch_has_single_step()))
                        return -EIO;
                user_enable_single_step(child);
        } else {
                user_disable_single_step(child);
        }

        child->exit_code = data;
        wake_up_state(child, __TASK_TRACED);

        return 0;
}

#ifdef CONFIG_HAVE_ARCH_TRACEHOOK

static const struct user_regset *
find_regset(const struct user_regset_view *view, unsigned int type)
{
        const struct user_regset *regset;
        int n;

        for (n = 0; n < view->n; ++n) {
                regset = view->regsets + n;
                if (regset->core_note_type == type)
                        return regset;
        }

        return NULL;
}

static int ptrace_regset(struct task_struct *task, int req, unsigned int type,
                         struct iovec *kiov)
{
        const struct user_regset_view *view = task_user_regset_view(task);
        const struct user_regset *regset = find_regset(view, type);
        int regset_no;

        if (!regset || (kiov->iov_len % regset->size) != 0)
                return -EINVAL;

        regset_no = regset - view->regsets;
        kiov->iov_len = min(kiov->iov_len,
                            (__kernel_size_t) (regset->n * regset->size));

        if (req == PTRACE_GETREGSET)
                return copy_regset_to_user(task, view, regset_no, 0,
                                           kiov->iov_len, kiov->iov_base);
        else
                return copy_regset_from_user(task, view, regset_no, 0,
                                             kiov->iov_len, kiov->iov_base);
}

#endif

int ptrace_request(struct task_struct *child, long request,
                   unsigned long addr, unsigned long data)
{
        bool seized = child->ptrace & PT_SEIZED;
        int ret = -EIO;
        siginfo_t siginfo, *si;
        void __user *datavp = (void __user *) data;
        unsigned long __user *datalp = datavp;
        unsigned long flags;

        switch (request) {
        case PTRACE_PEEKTEXT:
        case PTRACE_PEEKDATA:
                return generic_ptrace_peekdata(child, addr, data);
        case PTRACE_POKETEXT:
        case PTRACE_POKEDATA:
                return generic_ptrace_pokedata(child, addr, data);

#ifdef PTRACE_OLDSETOPTIONS
        case PTRACE_OLDSETOPTIONS:
#endif
        case PTRACE_SETOPTIONS:
                ret = ptrace_setoptions(child, data);
                break;
        case PTRACE_GETEVENTMSG:
                ret = put_user(child->ptrace_message, datalp);
                break;

        case PTRACE_GETSIGINFO:
                ret = ptrace_getsiginfo(child, &siginfo);
                if (!ret)
                        ret = copy_siginfo_to_user(datavp, &siginfo);
                break;

        case PTRACE_SETSIGINFO:
                if (copy_from_user(&siginfo, datavp, sizeof siginfo))
                        ret = -EFAULT;
                else
                        ret = ptrace_setsiginfo(child, &siginfo);
                break;

        case PTRACE_INTERRUPT:
                /*
                 * Stop tracee without any side-effect on signal or job
                 * control.  At least one trap is guaranteed to happen
                 * after this request.  If @child is already trapped, the
                 * current trap is not disturbed and another trap will
                 * happen after the current trap is ended with PTRACE_CONT.
                 *
                 * The actual trap might not be PTRACE_EVENT_STOP trap but
                 * the pending condition is cleared regardless.
                 */
                if (unlikely(!seized || !lock_task_sighand(child, &flags)))
                        break;

                /*
                 * INTERRUPT doesn't disturb existing trap sans one
                 * exception.  If ptracer issued LISTEN for the current
                 * STOP, this INTERRUPT should clear LISTEN and re-trap
                 * tracee into STOP.
                 */
                if (likely(task_set_jobctl_pending(child, JOBCTL_TRAP_STOP)))
                        ptrace_signal_wake_up(child, child->jobctl & JOBCTL_LISTENING);

                unlock_task_sighand(child, &flags);
                ret = 0;
                break;

        case PTRACE_LISTEN:
                /*
                 * Listen for events.  Tracee must be in STOP.  It's not
                 * resumed per-se but is not considered to be in TRACED by
                 * wait(2) or ptrace(2).  If an async event (e.g. group
                 * stop state change) happens, tracee will enter STOP trap
                 * again.  Alternatively, ptracer can issue INTERRUPT to
                 * finish listening and re-trap tracee into STOP.
                 */
                if (unlikely(!seized || !lock_task_sighand(child, &flags)))
                        break;

                si = child->last_siginfo;
                if (likely(si && (si->si_code >> 8) == PTRACE_EVENT_STOP)) {
                        child->jobctl |= JOBCTL_LISTENING;
                        /*
                         * If NOTIFY is set, it means event happened between
                         * start of this trap and now.  Trigger re-trap.
                         */
                        if (child->jobctl & JOBCTL_TRAP_NOTIFY)
                                ptrace_signal_wake_up(child, true);
                        ret = 0;
                }
                unlock_task_sighand(child, &flags);
                break;

        case PTRACE_DETACH:      /* detach a process that was attached. */
                ret = ptrace_detach(child, data);
                break;

#ifdef CONFIG_BINFMT_ELF_FDPIC
        case PTRACE_GETFDPIC: {
                struct mm_struct *mm = get_task_mm(child);
                unsigned long tmp = 0;

                ret = -ESRCH;
                if (!mm)
                        break;

                switch (addr) {
                case PTRACE_GETFDPIC_EXEC:
                        tmp = mm->context.exec_fdpic_loadmap;
                        break;
                case PTRACE_GETFDPIC_INTERP:
                        tmp = mm->context.interp_fdpic_loadmap;
                        break;
                default:
                        break;
                }
                mmput(mm);

                ret = put_user(tmp, datalp);
                break;
        }
#endif

#ifdef PTRACE_SINGLESTEP
        case PTRACE_SINGLESTEP:
#endif
#ifdef PTRACE_SINGLEBLOCK
        case PTRACE_SINGLEBLOCK:
#endif
#ifdef PTRACE_SYSEMU
        case PTRACE_SYSEMU:
        case PTRACE_SYSEMU_SINGLESTEP:
#endif
        case PTRACE_SYSCALL:
        case PTRACE_CONT:
                return ptrace_resume(child, request, data);

        case PTRACE_KILL:
                if (child->exit_state)  /* already dead */
                        return 0;
                return ptrace_resume(child, request, SIGKILL);

#ifdef CONFIG_HAVE_ARCH_TRACEHOOK
        case PTRACE_GETREGSET:
        case PTRACE_SETREGSET:
        {
                struct iovec kiov;
                struct iovec __user *uiov = datavp;

                if (!access_ok(VERIFY_WRITE, uiov, sizeof(*uiov)))
                        return -EFAULT;

                if (__get_user(kiov.iov_base, &uiov->iov_base) ||
                    __get_user(kiov.iov_len, &uiov->iov_len))
                        return -EFAULT;

                ret = ptrace_regset(child, request, addr, &kiov);
                if (!ret)
                        ret = __put_user(kiov.iov_len, &uiov->iov_len);
                break;
        }
#endif
        default:
                break;
        }

        return ret;
}

static struct task_struct *ptrace_get_task_struct(pid_t pid)
{
        struct task_struct *child;

        rcu_read_lock();
        child = find_task_by_vpid(pid);
        if (child)
                get_task_struct(child);
        rcu_read_unlock();

        if (!child)
                return ERR_PTR(-ESRCH);
        return child;
}

#ifndef arch_ptrace_attach
#define arch_ptrace_attach(child)       do { } while (0)
#endif

SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr,
                unsigned long, data)
{
        struct task_struct *child;
        long ret;

        if (request == PTRACE_TRACEME) {
                ret = ptrace_traceme();
                if (!ret)
                        arch_ptrace_attach(current);
                goto out;
        }

        child = ptrace_get_task_struct(pid);
        if (IS_ERR(child)) {
                ret = PTR_ERR(child);
                goto out;
        }

        if (request == PTRACE_ATTACH || request == PTRACE_SEIZE) {
                ret = ptrace_attach(child, request, addr, data);
                /*
                 * Some architectures need to do book-keeping after
                 * a ptrace attach.
                 */
                if (!ret)
                        arch_ptrace_attach(child);
                goto out_put_task_struct;
        }

        ret = ptrace_check_attach(child, request == PTRACE_KILL ||
                                  request == PTRACE_INTERRUPT);
        if (ret < 0)
                goto out_put_task_struct;

        ret = arch_ptrace(child, request, addr, data);
        if (ret || request != PTRACE_DETACH)
                ptrace_unfreeze_traced(child);

 out_put_task_struct:
        put_task_struct(child);
 out:
        return ret;
}

int generic_ptrace_peekdata(struct task_struct *tsk, unsigned long addr,
                            unsigned long data)
{
        unsigned long tmp;
        int copied;

        copied = access_process_vm(tsk, addr, &tmp, sizeof(tmp), 0);
        if (copied != sizeof(tmp))
                return -EIO;
        return put_user(tmp, (unsigned long __user *)data);
}

int generic_ptrace_pokedata(struct task_struct *tsk, unsigned long addr,
                            unsigned long data)
{
        int copied;

        copied = access_process_vm(tsk, addr, &data, sizeof(data), 1);
        return (copied == sizeof(data)) ? 0 : -EIO;
}

#if defined CONFIG_COMPAT
#include <linux/compat.h>

int compat_ptrace_request(struct task_struct *child, compat_long_t request,
                          compat_ulong_t addr, compat_ulong_t data)
{
        compat_ulong_t __user *datap = compat_ptr(data);
        compat_ulong_t word;
        siginfo_t siginfo;
        int ret;

        switch (request) {
        case PTRACE_PEEKTEXT:
        case PTRACE_PEEKDATA:
                ret = access_process_vm(child, addr, &word, sizeof(word), 0);
                if (ret != sizeof(word))
                        ret = -EIO;
                else
                        ret = put_user(word, datap);
                break;

        case PTRACE_POKETEXT:
        case PTRACE_POKEDATA:
                ret = access_process_vm(child, addr, &data, sizeof(data), 1);
                ret = (ret != sizeof(data) ? -EIO : 0);
                break;

        case PTRACE_GETEVENTMSG:
                ret = put_user((compat_ulong_t) child->ptrace_message, datap);
                break;

        case PTRACE_GETSIGINFO:
                ret = ptrace_getsiginfo(child, &siginfo);
                if (!ret)
                        ret = copy_siginfo_to_user32(
                                (struct compat_siginfo __user *) datap,
                                &siginfo);
                break;

        case PTRACE_SETSIGINFO:
                memset(&siginfo, 0, sizeof siginfo);
                if (copy_siginfo_from_user32(
                            &siginfo, (struct compat_siginfo __user *) datap))
                        ret = -EFAULT;
                else
                        ret = ptrace_setsiginfo(child, &siginfo);
                break;
#ifdef CONFIG_HAVE_ARCH_TRACEHOOK
        case PTRACE_GETREGSET:
        case PTRACE_SETREGSET:
        {
                struct iovec kiov;
                struct compat_iovec __user *uiov =
                        (struct compat_iovec __user *) datap;
                compat_uptr_t ptr;
                compat_size_t len;

                if (!access_ok(VERIFY_WRITE, uiov, sizeof(*uiov)))
                        return -EFAULT;

                if (__get_user(ptr, &uiov->iov_base) ||
                    __get_user(len, &uiov->iov_len))
                        return -EFAULT;

                kiov.iov_base = compat_ptr(ptr);
                kiov.iov_len = len;

                ret = ptrace_regset(child, request, addr, &kiov);
                if (!ret)
                        ret = __put_user(kiov.iov_len, &uiov->iov_len);
                break;
        }
#endif

        default:
                ret = ptrace_request(child, request, addr, data);
        }

        return ret;
}

asmlinkage long compat_sys_ptrace(compat_long_t request, compat_long_t pid,
                                  compat_long_t addr, compat_long_t data)
{
        struct task_struct *child;
        long ret;

        if (request == PTRACE_TRACEME) {
                ret = ptrace_traceme();
                goto out;
        }

        child = ptrace_get_task_struct(pid);
        if (IS_ERR(child)) {
                ret = PTR_ERR(child);
                goto out;
        }

        if (request == PTRACE_ATTACH || request == PTRACE_SEIZE) {
                ret = ptrace_attach(child, request, addr, data);
                /*
                 * Some architectures need to do book-keeping after
                 * a ptrace attach.
                 */
                if (!ret)
                        arch_ptrace_attach(child);
                goto out_put_task_struct;
        }

        ret = ptrace_check_attach(child, request == PTRACE_KILL ||
                                  request == PTRACE_INTERRUPT);
        if (!ret) {
                ret = compat_arch_ptrace(child, request, addr, data);
                if (ret || request != PTRACE_DETACH)
                        ptrace_unfreeze_traced(child);
        }

 out_put_task_struct:
        put_task_struct(child);
 out:
        return ret;
}
#endif  /* CONFIG_COMPAT */

#ifdef CONFIG_HAVE_HW_BREAKPOINT
int ptrace_get_breakpoints(struct task_struct *tsk)
{
        if (atomic_inc_not_zero(&tsk->ptrace_bp_refcnt))
                return 0;

        return -1;
}

void ptrace_put_breakpoints(struct task_struct *tsk)
{
        if (atomic_dec_and_test(&tsk->ptrace_bp_refcnt))
                flush_ptrace_hw_breakpoint(tsk);
}
#endif /* CONFIG_HAVE_HW_BREAKPOINT */