/*
 * 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/module.h>
#include <linux/sched.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/smp_lock.h>
#include <linux/ptrace.h>
#include <linux/security.h>
#include <linux/signal.h>

#include <asm/pgtable.h>
#include <asm/uaccess.h>

/*
 * 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_list));
        if (child->parent == new_parent)
                return;
        list_add(&child->ptrace_list, &child->parent->ptrace_children);
        remove_parent(child);
        child->parent = new_parent;
        add_parent(child);
}
 
/*
 * Turn a tracing stop into a normal stop now, since with no tracer there
 * would be no way to wake it up with SIGCONT or SIGKILL.  If there was a
 * signal sent that would resume the child, but didn't because it was in
 * TASK_TRACED, resume it now.
 * Requires that irqs be disabled.
 */
void ptrace_untrace(struct task_struct *child)
{
        spin_lock(&child->sighand->siglock);
        if (child->state == TASK_TRACED) {
                if (child->signal->flags & SIGNAL_STOP_STOPPED) {
                        child->state = TASK_STOPPED;
                } else {
                        signal_wake_up(child, 1);
                }
        }
        spin_unlock(&child->sighand->siglock);
}

/*
 * unptrace a task: move it back to its original parent and
 * remove it from the ptrace list.
 *
 * Must be called with the tasklist lock write-held.
 */
void __ptrace_unlink(struct task_struct *child)
{
        BUG_ON(!child->ptrace);

        child->ptrace = 0;
        if (!list_empty(&child->ptrace_list)) {
                list_del_init(&child->ptrace_list);
                remove_parent(child);
                child->parent = child->real_parent;
                add_parent(child);
        }

        if (child->state == TASK_TRACED)
                ptrace_untrace(child);
}

/*
 * Check that we have indeed attached to the thing..
 */
int ptrace_check_attach(struct task_struct *child, int kill)
{
        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 & PT_PTRACED) && child->parent == current &&
            (!(child->ptrace & PT_ATTACHED) || child->real_parent != current)
            && child->signal != NULL) {
                ret = 0;
                spin_lock_irq(&child->sighand->siglock);
                if (child->state == TASK_STOPPED) {
                        child->state = TASK_TRACED;
                } else if (child->state != TASK_TRACED && !kill) {
                        ret = -ESRCH;
                }
                spin_unlock_irq(&child->sighand->siglock);
        }
        read_unlock(&tasklist_lock);

        if (!ret && !kill) {
                wait_task_inactive(child);
        }

        /* All systems go.. */
        return ret;
}

static int may_attach(struct task_struct *task)
{
        /* 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;
        if (((current->uid != task->euid) ||
             (current->uid != task->suid) ||
             (current->uid != task->uid) ||
             (current->gid != task->egid) ||
             (current->gid != task->sgid) ||
             (current->gid != task->gid)) && !capable(CAP_SYS_PTRACE))
                return -EPERM;
        smp_rmb();
        if (task->mm)
                dumpable = task->mm->dumpable;
        if (!dumpable && !capable(CAP_SYS_PTRACE))
                return -EPERM;

        return security_ptrace(current, task);
}

int ptrace_may_attach(struct task_struct *task)
{
        int err;
        task_lock(task);
        err = may_attach(task);
        task_unlock(task);
        return !err;
}

int ptrace_attach(struct task_struct *task)
{
        int retval;

        retval = -EPERM;
        if (task->pid <= 1)
                goto out;
        if (task->tgid == current->tgid)
                goto out;

repeat:
        /*
         * Nasty, nasty.
         *
         * We want to hold both the task-lock and the
         * tasklist_lock for writing at the same time.
         * But that's against the rules (tasklist_lock
         * is taken for reading by interrupts on other
         * cpu's that may have task_lock).
         */
        task_lock(task);
        local_irq_disable();
        if (!write_trylock(&tasklist_lock)) {
                local_irq_enable();
                task_unlock(task);
                do {
                        cpu_relax();
                } while (!write_can_lock(&tasklist_lock));
                goto repeat;
        }

        if (!task->mm)
                goto bad;
        /* the same process cannot be attached many times */
        if (task->ptrace & PT_PTRACED)
                goto bad;
        retval = may_attach(task);
        if (retval)
                goto bad;

        /* Go */
        task->ptrace |= PT_PTRACED | ((task->real_parent != current)
                                      ? PT_ATTACHED : 0);
        if (capable(CAP_SYS_PTRACE))
                task->ptrace |= PT_PTRACE_CAP;

        __ptrace_link(task, current);

        force_sig_specific(SIGSTOP, task);

bad:
        write_unlock_irq(&tasklist_lock);
        task_unlock(task);
out:
        return retval;
}

static inline void __ptrace_detach(struct task_struct *child, unsigned int data)
{
        child->exit_code = data;
        /* .. re-parent .. */
        __ptrace_unlink(child);
        /* .. and wake it up. */
        if (child->exit_state != EXIT_ZOMBIE)
                wake_up_process(child);
}

int ptrace_detach(struct task_struct *child, unsigned int data)
{
        if (!valid_signal(data))
                return -EIO;

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

        write_lock_irq(&tasklist_lock);
        /* protect against de_thread()->release_task() */
        if (child->ptrace)
                __ptrace_detach(child, data);
        write_unlock_irq(&tasklist_lock);

        return 0;
}

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, long data)
{
        child->ptrace &= ~PT_TRACE_MASK;

        if (data & PTRACE_O_TRACESYSGOOD)
                child->ptrace |= PT_TRACESYSGOOD;

        if (data & PTRACE_O_TRACEFORK)
                child->ptrace |= PT_TRACE_FORK;

        if (data & PTRACE_O_TRACEVFORK)
                child->ptrace |= PT_TRACE_VFORK;

        if (data & PTRACE_O_TRACECLONE)
                child->ptrace |= PT_TRACE_CLONE;

        if (data & PTRACE_O_TRACEEXEC)
                child->ptrace |= PT_TRACE_EXEC;

        if (data & PTRACE_O_TRACEVFORKDONE)
                child->ptrace |= PT_TRACE_VFORK_DONE;

        if (data & PTRACE_O_TRACEEXIT)
                child->ptrace |= PT_TRACE_EXIT;

        return (data & ~PTRACE_O_MASK) ? -EINVAL : 0;
}

static int ptrace_getsiginfo(struct task_struct *child, siginfo_t __user * data)
{
        siginfo_t lastinfo;
        int error = -ESRCH;

        read_lock(&tasklist_lock);
        if (likely(child->sighand != NULL)) {
                error = -EINVAL;
                spin_lock_irq(&child->sighand->siglock);
                if (likely(child->last_siginfo != NULL)) {
                        lastinfo = *child->last_siginfo;
                        error = 0;
                }
                spin_unlock_irq(&child->sighand->siglock);
        }
        read_unlock(&tasklist_lock);
        if (!error)
                return copy_siginfo_to_user(data, &lastinfo);
        return error;
}

static int ptrace_setsiginfo(struct task_struct *child, siginfo_t __user * data)
{
        siginfo_t newinfo;
        int error = -ESRCH;

        if (copy_from_user(&newinfo, data, sizeof (siginfo_t)))
                return -EFAULT;

        read_lock(&tasklist_lock);
        if (likely(child->sighand != NULL)) {
                error = -EINVAL;
                spin_lock_irq(&child->sighand->siglock);
                if (likely(child->last_siginfo != NULL)) {
                        *child->last_siginfo = newinfo;
                        error = 0;
                }
                spin_unlock_irq(&child->sighand->siglock);
        }
        read_unlock(&tasklist_lock);
        return error;
}

int ptrace_request(struct task_struct *child, long request,
                   long addr, long data)
{
        int ret = -EIO;

        switch (request) {
#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, (unsigned long __user *) data);
                break;
        case PTRACE_GETSIGINFO:
                ret = ptrace_getsiginfo(child, (siginfo_t __user *) data);
                break;
        case PTRACE_SETSIGINFO:
                ret = ptrace_setsiginfo(child, (siginfo_t __user *) data);
                break;
        default:
                break;
        }

        return ret;
}

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

        /*
         * Are we already being traced?
         */
        task_lock(current);
        if (!(current->ptrace & PT_PTRACED)) {
                ret = security_ptrace(current->parent, current);
                /*
                 * Set the ptrace bit in the process ptrace flags.
                 */
                if (!ret)
                        current->ptrace |= PT_PTRACED;
        }
        task_unlock(current);
        return ret;
}

/**
 * ptrace_get_task_struct  --  grab a task struct reference for ptrace
 * @pid:       process id to grab a task_struct reference of
 *
 * This function is a helper for ptrace implementations.  It checks
 * permissions and then grabs a task struct for use of the actual
 * ptrace implementation.
 *
 * Returns the task_struct for @pid or an ERR_PTR() on failure.
 */
struct task_struct *ptrace_get_task_struct(pid_t pid)
{
        struct task_struct *child;

        /*
         * Tracing init is not allowed.
         */
        if (pid == 1)
                return ERR_PTR(-EPERM);

        read_lock(&tasklist_lock);
        child = find_task_by_pid(pid);
        if (child)
                get_task_struct(child);

        read_unlock(&tasklist_lock);
        if (!child)
                return ERR_PTR(-ESRCH);
        return child;
}

#ifndef __ARCH_SYS_PTRACE
asmlinkage long sys_ptrace(long request, long pid, long addr, long data)
{
        struct task_struct *child;
        long ret;

        /*
         * This lock_kernel fixes a subtle race with suid exec
         */
        lock_kernel();
        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) {
                ret = ptrace_attach(child);
                goto out_put_task_struct;
        }

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

        ret = arch_ptrace(child, request, addr, data);
        if (ret < 0)
                goto out_put_task_struct;

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