signal.c 69.3 KB
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/*
 *  linux/kernel/signal.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 *
 *  1997-11-02  Modified for POSIX.1b signals by Richard Henderson
 *
 *  2003-06-02  Jim Houston - Concurrent Computer Corp.
 *		Changes to use preallocated sigqueue structures
 *		to allow signals to be sent reliably.
 */

#include <linux/config.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/smp_lock.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/tty.h>
#include <linux/binfmts.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/ptrace.h>
#include <linux/posix-timers.h>
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#include <linux/signal.h>
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#include <linux/audit.h>
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#include <asm/param.h>
#include <asm/uaccess.h>
#include <asm/unistd.h>
#include <asm/siginfo.h>

/*
 * SLAB caches for signal bits.
 */

static kmem_cache_t *sigqueue_cachep;

/*
 * In POSIX a signal is sent either to a specific thread (Linux task)
 * or to the process as a whole (Linux thread group).  How the signal
 * is sent determines whether it's to one thread or the whole group,
 * which determines which signal mask(s) are involved in blocking it
 * from being delivered until later.  When the signal is delivered,
 * either it's caught or ignored by a user handler or it has a default
 * effect that applies to the whole thread group (POSIX process).
 *
 * The possible effects an unblocked signal set to SIG_DFL can have are:
 *   ignore	- Nothing Happens
 *   terminate	- kill the process, i.e. all threads in the group,
 * 		  similar to exit_group.  The group leader (only) reports
 *		  WIFSIGNALED status to its parent.
 *   coredump	- write a core dump file describing all threads using
 *		  the same mm and then kill all those threads
 *   stop 	- stop all the threads in the group, i.e. TASK_STOPPED state
 *
 * SIGKILL and SIGSTOP cannot be caught, blocked, or ignored.
 * Other signals when not blocked and set to SIG_DFL behaves as follows.
 * The job control signals also have other special effects.
 *
 *	+--------------------+------------------+
 *	|  POSIX signal      |  default action  |
 *	+--------------------+------------------+
 *	|  SIGHUP            |  terminate	|
 *	|  SIGINT            |	terminate	|
 *	|  SIGQUIT           |	coredump 	|
 *	|  SIGILL            |	coredump 	|
 *	|  SIGTRAP           |	coredump 	|
 *	|  SIGABRT/SIGIOT    |	coredump 	|
 *	|  SIGBUS            |	coredump 	|
 *	|  SIGFPE            |	coredump 	|
 *	|  SIGKILL           |	terminate(+)	|
 *	|  SIGUSR1           |	terminate	|
 *	|  SIGSEGV           |	coredump 	|
 *	|  SIGUSR2           |	terminate	|
 *	|  SIGPIPE           |	terminate	|
 *	|  SIGALRM           |	terminate	|
 *	|  SIGTERM           |	terminate	|
 *	|  SIGCHLD           |	ignore   	|
 *	|  SIGCONT           |	ignore(*)	|
 *	|  SIGSTOP           |	stop(*)(+)  	|
 *	|  SIGTSTP           |	stop(*)  	|
 *	|  SIGTTIN           |	stop(*)  	|
 *	|  SIGTTOU           |	stop(*)  	|
 *	|  SIGURG            |	ignore   	|
 *	|  SIGXCPU           |	coredump 	|
 *	|  SIGXFSZ           |	coredump 	|
 *	|  SIGVTALRM         |	terminate	|
 *	|  SIGPROF           |	terminate	|
 *	|  SIGPOLL/SIGIO     |	terminate	|
 *	|  SIGSYS/SIGUNUSED  |	coredump 	|
 *	|  SIGSTKFLT         |	terminate	|
 *	|  SIGWINCH          |	ignore   	|
 *	|  SIGPWR            |	terminate	|
 *	|  SIGRTMIN-SIGRTMAX |	terminate       |
 *	+--------------------+------------------+
 *	|  non-POSIX signal  |  default action  |
 *	+--------------------+------------------+
 *	|  SIGEMT            |  coredump	|
 *	+--------------------+------------------+
 *
 * (+) For SIGKILL and SIGSTOP the action is "always", not just "default".
 * (*) Special job control effects:
 * When SIGCONT is sent, it resumes the process (all threads in the group)
 * from TASK_STOPPED state and also clears any pending/queued stop signals
 * (any of those marked with "stop(*)").  This happens regardless of blocking,
 * catching, or ignoring SIGCONT.  When any stop signal is sent, it clears
 * any pending/queued SIGCONT signals; this happens regardless of blocking,
 * catching, or ignored the stop signal, though (except for SIGSTOP) the
 * default action of stopping the process may happen later or never.
 */

#ifdef SIGEMT
#define M_SIGEMT	M(SIGEMT)
#else
#define M_SIGEMT	0
#endif

#if SIGRTMIN > BITS_PER_LONG
#define M(sig) (1ULL << ((sig)-1))
#else
#define M(sig) (1UL << ((sig)-1))
#endif
#define T(sig, mask) (M(sig) & (mask))

#define SIG_KERNEL_ONLY_MASK (\
	M(SIGKILL)   |  M(SIGSTOP)                                   )

#define SIG_KERNEL_STOP_MASK (\
	M(SIGSTOP)   |  M(SIGTSTP)   |  M(SIGTTIN)   |  M(SIGTTOU)   )

#define SIG_KERNEL_COREDUMP_MASK (\
        M(SIGQUIT)   |  M(SIGILL)    |  M(SIGTRAP)   |  M(SIGABRT)   | \
        M(SIGFPE)    |  M(SIGSEGV)   |  M(SIGBUS)    |  M(SIGSYS)    | \
        M(SIGXCPU)   |  M(SIGXFSZ)   |  M_SIGEMT                     )

#define SIG_KERNEL_IGNORE_MASK (\
        M(SIGCONT)   |  M(SIGCHLD)   |  M(SIGWINCH)  |  M(SIGURG)    )

#define sig_kernel_only(sig) \
		(((sig) < SIGRTMIN)  && T(sig, SIG_KERNEL_ONLY_MASK))
#define sig_kernel_coredump(sig) \
		(((sig) < SIGRTMIN)  && T(sig, SIG_KERNEL_COREDUMP_MASK))
#define sig_kernel_ignore(sig) \
		(((sig) < SIGRTMIN)  && T(sig, SIG_KERNEL_IGNORE_MASK))
#define sig_kernel_stop(sig) \
		(((sig) < SIGRTMIN)  && T(sig, SIG_KERNEL_STOP_MASK))

#define sig_user_defined(t, signr) \
	(((t)->sighand->action[(signr)-1].sa.sa_handler != SIG_DFL) &&	\
	 ((t)->sighand->action[(signr)-1].sa.sa_handler != SIG_IGN))

#define sig_fatal(t, signr) \
	(!T(signr, SIG_KERNEL_IGNORE_MASK|SIG_KERNEL_STOP_MASK) && \
	 (t)->sighand->action[(signr)-1].sa.sa_handler == SIG_DFL)

static int sig_ignored(struct task_struct *t, int sig)
{
	void __user * handler;

	/*
	 * Tracers always want to know about signals..
	 */
	if (t->ptrace & PT_PTRACED)
		return 0;

	/*
	 * Blocked signals are never ignored, since the
	 * signal handler may change by the time it is
	 * unblocked.
	 */
	if (sigismember(&t->blocked, sig))
		return 0;

	/* Is it explicitly or implicitly ignored? */
	handler = t->sighand->action[sig-1].sa.sa_handler;
	return   handler == SIG_IGN ||
		(handler == SIG_DFL && sig_kernel_ignore(sig));
}

/*
 * Re-calculate pending state from the set of locally pending
 * signals, globally pending signals, and blocked signals.
 */
static inline int has_pending_signals(sigset_t *signal, sigset_t *blocked)
{
	unsigned long ready;
	long i;

	switch (_NSIG_WORDS) {
	default:
		for (i = _NSIG_WORDS, ready = 0; --i >= 0 ;)
			ready |= signal->sig[i] &~ blocked->sig[i];
		break;

	case 4: ready  = signal->sig[3] &~ blocked->sig[3];
		ready |= signal->sig[2] &~ blocked->sig[2];
		ready |= signal->sig[1] &~ blocked->sig[1];
		ready |= signal->sig[0] &~ blocked->sig[0];
		break;

	case 2: ready  = signal->sig[1] &~ blocked->sig[1];
		ready |= signal->sig[0] &~ blocked->sig[0];
		break;

	case 1: ready  = signal->sig[0] &~ blocked->sig[0];
	}
	return ready !=	0;
}

#define PENDING(p,b) has_pending_signals(&(p)->signal, (b))

fastcall void recalc_sigpending_tsk(struct task_struct *t)
{
	if (t->signal->group_stop_count > 0 ||
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	    (freezing(t)) ||
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	    PENDING(&t->pending, &t->blocked) ||
	    PENDING(&t->signal->shared_pending, &t->blocked))
		set_tsk_thread_flag(t, TIF_SIGPENDING);
	else
		clear_tsk_thread_flag(t, TIF_SIGPENDING);
}

void recalc_sigpending(void)
{
	recalc_sigpending_tsk(current);
}

/* Given the mask, find the first available signal that should be serviced. */

static int
next_signal(struct sigpending *pending, sigset_t *mask)
{
	unsigned long i, *s, *m, x;
	int sig = 0;
	
	s = pending->signal.sig;
	m = mask->sig;
	switch (_NSIG_WORDS) {
	default:
		for (i = 0; i < _NSIG_WORDS; ++i, ++s, ++m)
			if ((x = *s &~ *m) != 0) {
				sig = ffz(~x) + i*_NSIG_BPW + 1;
				break;
			}
		break;

	case 2: if ((x = s[0] &~ m[0]) != 0)
			sig = 1;
		else if ((x = s[1] &~ m[1]) != 0)
			sig = _NSIG_BPW + 1;
		else
			break;
		sig += ffz(~x);
		break;

	case 1: if ((x = *s &~ *m) != 0)
			sig = ffz(~x) + 1;
		break;
	}
	
	return sig;
}

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static struct sigqueue *__sigqueue_alloc(struct task_struct *t, gfp_t flags,
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					 int override_rlimit)
{
	struct sigqueue *q = NULL;

	atomic_inc(&t->user->sigpending);
	if (override_rlimit ||
	    atomic_read(&t->user->sigpending) <=
			t->signal->rlim[RLIMIT_SIGPENDING].rlim_cur)
		q = kmem_cache_alloc(sigqueue_cachep, flags);
	if (unlikely(q == NULL)) {
		atomic_dec(&t->user->sigpending);
	} else {
		INIT_LIST_HEAD(&q->list);
		q->flags = 0;
		q->user = get_uid(t->user);
	}
	return(q);
}

static inline void __sigqueue_free(struct sigqueue *q)
{
	if (q->flags & SIGQUEUE_PREALLOC)
		return;
	atomic_dec(&q->user->sigpending);
	free_uid(q->user);
	kmem_cache_free(sigqueue_cachep, q);
}

static void flush_sigqueue(struct sigpending *queue)
{
	struct sigqueue *q;

	sigemptyset(&queue->signal);
	while (!list_empty(&queue->list)) {
		q = list_entry(queue->list.next, struct sigqueue , list);
		list_del_init(&q->list);
		__sigqueue_free(q);
	}
}

/*
 * Flush all pending signals for a task.
 */

void
flush_signals(struct task_struct *t)
{
	unsigned long flags;

	spin_lock_irqsave(&t->sighand->siglock, flags);
	clear_tsk_thread_flag(t,TIF_SIGPENDING);
	flush_sigqueue(&t->pending);
	flush_sigqueue(&t->signal->shared_pending);
	spin_unlock_irqrestore(&t->sighand->siglock, flags);
}

/*
 * This function expects the tasklist_lock write-locked.
 */
void __exit_sighand(struct task_struct *tsk)
{
	struct sighand_struct * sighand = tsk->sighand;

	/* Ok, we're done with the signal handlers */
	tsk->sighand = NULL;
	if (atomic_dec_and_test(&sighand->count))
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		sighand_free(sighand);
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}

void exit_sighand(struct task_struct *tsk)
{
	write_lock_irq(&tasklist_lock);
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	rcu_read_lock();
	if (tsk->sighand != NULL) {
		struct sighand_struct *sighand = rcu_dereference(tsk->sighand);
		spin_lock(&sighand->siglock);
		__exit_sighand(tsk);
		spin_unlock(&sighand->siglock);
	}
	rcu_read_unlock();
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	write_unlock_irq(&tasklist_lock);
}

/*
 * This function expects the tasklist_lock write-locked.
 */
void __exit_signal(struct task_struct *tsk)
{
	struct signal_struct * sig = tsk->signal;
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	struct sighand_struct * sighand;
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	if (!sig)
		BUG();
	if (!atomic_read(&sig->count))
		BUG();
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	rcu_read_lock();
	sighand = rcu_dereference(tsk->sighand);
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	spin_lock(&sighand->siglock);
	posix_cpu_timers_exit(tsk);
	if (atomic_dec_and_test(&sig->count)) {
		posix_cpu_timers_exit_group(tsk);
		if (tsk == sig->curr_target)
			sig->curr_target = next_thread(tsk);
		tsk->signal = NULL;
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		__exit_sighand(tsk);
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		spin_unlock(&sighand->siglock);
		flush_sigqueue(&sig->shared_pending);
	} else {
		/*
		 * If there is any task waiting for the group exit
		 * then notify it:
		 */
		if (sig->group_exit_task && atomic_read(&sig->count) == sig->notify_count) {
			wake_up_process(sig->group_exit_task);
			sig->group_exit_task = NULL;
		}
		if (tsk == sig->curr_target)
			sig->curr_target = next_thread(tsk);
		tsk->signal = NULL;
		/*
		 * Accumulate here the counters for all threads but the
		 * group leader as they die, so they can be added into
		 * the process-wide totals when those are taken.
		 * The group leader stays around as a zombie as long
		 * as there are other threads.  When it gets reaped,
		 * the exit.c code will add its counts into these totals.
		 * We won't ever get here for the group leader, since it
		 * will have been the last reference on the signal_struct.
		 */
		sig->utime = cputime_add(sig->utime, tsk->utime);
		sig->stime = cputime_add(sig->stime, tsk->stime);
		sig->min_flt += tsk->min_flt;
		sig->maj_flt += tsk->maj_flt;
		sig->nvcsw += tsk->nvcsw;
		sig->nivcsw += tsk->nivcsw;
		sig->sched_time += tsk->sched_time;
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		__exit_sighand(tsk);
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		spin_unlock(&sighand->siglock);
		sig = NULL;	/* Marker for below.  */
	}
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	rcu_read_unlock();
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	clear_tsk_thread_flag(tsk,TIF_SIGPENDING);
	flush_sigqueue(&tsk->pending);
	if (sig) {
		/*
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		 * We are cleaning up the signal_struct here.
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		 */
		exit_thread_group_keys(sig);
		kmem_cache_free(signal_cachep, sig);
	}
}

void exit_signal(struct task_struct *tsk)
{
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	atomic_dec(&tsk->signal->live);

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	write_lock_irq(&tasklist_lock);
	__exit_signal(tsk);
	write_unlock_irq(&tasklist_lock);
}

/*
 * Flush all handlers for a task.
 */

void
flush_signal_handlers(struct task_struct *t, int force_default)
{
	int i;
	struct k_sigaction *ka = &t->sighand->action[0];
	for (i = _NSIG ; i != 0 ; i--) {
		if (force_default || ka->sa.sa_handler != SIG_IGN)
			ka->sa.sa_handler = SIG_DFL;
		ka->sa.sa_flags = 0;
		sigemptyset(&ka->sa.sa_mask);
		ka++;
	}
}


/* Notify the system that a driver wants to block all signals for this
 * process, and wants to be notified if any signals at all were to be
 * sent/acted upon.  If the notifier routine returns non-zero, then the
 * signal will be acted upon after all.  If the notifier routine returns 0,
 * then then signal will be blocked.  Only one block per process is
 * allowed.  priv is a pointer to private data that the notifier routine
 * can use to determine if the signal should be blocked or not.  */

void
block_all_signals(int (*notifier)(void *priv), void *priv, sigset_t *mask)
{
	unsigned long flags;

	spin_lock_irqsave(&current->sighand->siglock, flags);
	current->notifier_mask = mask;
	current->notifier_data = priv;
	current->notifier = notifier;
	spin_unlock_irqrestore(&current->sighand->siglock, flags);
}

/* Notify the system that blocking has ended. */

void
unblock_all_signals(void)
{
	unsigned long flags;

	spin_lock_irqsave(&current->sighand->siglock, flags);
	current->notifier = NULL;
	current->notifier_data = NULL;
	recalc_sigpending();
	spin_unlock_irqrestore(&current->sighand->siglock, flags);
}

static inline int collect_signal(int sig, struct sigpending *list, siginfo_t *info)
{
	struct sigqueue *q, *first = NULL;
	int still_pending = 0;

	if (unlikely(!sigismember(&list->signal, sig)))
		return 0;

	/*
	 * Collect the siginfo appropriate to this signal.  Check if
	 * there is another siginfo for the same signal.
	*/
	list_for_each_entry(q, &list->list, list) {
		if (q->info.si_signo == sig) {
			if (first) {
				still_pending = 1;
				break;
			}
			first = q;
		}
	}
	if (first) {
		list_del_init(&first->list);
		copy_siginfo(info, &first->info);
		__sigqueue_free(first);
		if (!still_pending)
			sigdelset(&list->signal, sig);
	} else {

		/* Ok, it wasn't in the queue.  This must be
		   a fast-pathed signal or we must have been
		   out of queue space.  So zero out the info.
		 */
		sigdelset(&list->signal, sig);
		info->si_signo = sig;
		info->si_errno = 0;
		info->si_code = 0;
		info->si_pid = 0;
		info->si_uid = 0;
	}
	return 1;
}

static int __dequeue_signal(struct sigpending *pending, sigset_t *mask,
			siginfo_t *info)
{
	int sig = 0;

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	sig = next_signal(pending, mask);
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	if (sig) {
		if (current->notifier) {
			if (sigismember(current->notifier_mask, sig)) {
				if (!(current->notifier)(current->notifier_data)) {
					clear_thread_flag(TIF_SIGPENDING);
					return 0;
				}
			}
		}

		if (!collect_signal(sig, pending, info))
			sig = 0;
				
	}
	recalc_sigpending();

	return sig;
}

/*
 * Dequeue a signal and return the element to the caller, which is 
 * expected to free it.
 *
 * All callers have to hold the siglock.
 */
int dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info)
{
	int signr = __dequeue_signal(&tsk->pending, mask, info);
	if (!signr)
		signr = __dequeue_signal(&tsk->signal->shared_pending,
					 mask, info);
 	if (signr && unlikely(sig_kernel_stop(signr))) {
 		/*
 		 * Set a marker that we have dequeued a stop signal.  Our
 		 * caller might release the siglock and then the pending
 		 * stop signal it is about to process is no longer in the
 		 * pending bitmasks, but must still be cleared by a SIGCONT
 		 * (and overruled by a SIGKILL).  So those cases clear this
 		 * shared flag after we've set it.  Note that this flag may
 		 * remain set after the signal we return is ignored or
 		 * handled.  That doesn't matter because its only purpose
 		 * is to alert stop-signal processing code when another
 		 * processor has come along and cleared the flag.
 		 */
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 		if (!(tsk->signal->flags & SIGNAL_GROUP_EXIT))
 			tsk->signal->flags |= SIGNAL_STOP_DEQUEUED;
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 	}
	if ( signr &&
	     ((info->si_code & __SI_MASK) == __SI_TIMER) &&
	     info->si_sys_private){
		/*
		 * Release the siglock to ensure proper locking order
		 * of timer locks outside of siglocks.  Note, we leave
		 * irqs disabled here, since the posix-timers code is
		 * about to disable them again anyway.
		 */
		spin_unlock(&tsk->sighand->siglock);
		do_schedule_next_timer(info);
		spin_lock(&tsk->sighand->siglock);
	}
	return signr;
}

/*
 * Tell a process that it has a new active signal..
 *
 * NOTE! we rely on the previous spin_lock to
 * lock interrupts for us! We can only be called with
 * "siglock" held, and the local interrupt must
 * have been disabled when that got acquired!
 *
 * No need to set need_resched since signal event passing
 * goes through ->blocked
 */
void signal_wake_up(struct task_struct *t, int resume)
{
	unsigned int mask;

	set_tsk_thread_flag(t, TIF_SIGPENDING);

	/*
	 * For SIGKILL, we want to wake it up in the stopped/traced case.
	 * We don't check t->state here because there is a race with it
	 * executing another processor and just now entering stopped state.
	 * By using wake_up_state, we ensure the process will wake up and
	 * handle its death signal.
	 */
	mask = TASK_INTERRUPTIBLE;
	if (resume)
		mask |= TASK_STOPPED | TASK_TRACED;
	if (!wake_up_state(t, mask))
		kick_process(t);
}

/*
 * Remove signals in mask from the pending set and queue.
 * Returns 1 if any signals were found.
 *
 * All callers must be holding the siglock.
 */
static int rm_from_queue(unsigned long mask, struct sigpending *s)
{
	struct sigqueue *q, *n;

	if (!sigtestsetmask(&s->signal, mask))
		return 0;

	sigdelsetmask(&s->signal, mask);
	list_for_each_entry_safe(q, n, &s->list, list) {
		if (q->info.si_signo < SIGRTMIN &&
		    (mask & sigmask(q->info.si_signo))) {
			list_del_init(&q->list);
			__sigqueue_free(q);
		}
	}
	return 1;
}

/*
 * Bad permissions for sending the signal
 */
static int check_kill_permission(int sig, struct siginfo *info,
				 struct task_struct *t)
{
	int error = -EINVAL;
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	if (!valid_signal(sig))
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		return error;
	error = -EPERM;
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	if ((info == SEND_SIG_NOINFO || (!is_si_special(info) && SI_FROMUSER(info)))
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	    && ((sig != SIGCONT) ||
		(current->signal->session != t->signal->session))
	    && (current->euid ^ t->suid) && (current->euid ^ t->uid)
	    && (current->uid ^ t->suid) && (current->uid ^ t->uid)
	    && !capable(CAP_KILL))
		return error;
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	error = security_task_kill(t, info, sig);
	if (!error)
		audit_signal_info(sig, t); /* Let audit system see the signal */
	return error;
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}

/* forward decl */
static void do_notify_parent_cldstop(struct task_struct *tsk,
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				     int to_self,
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				     int why);

/*
 * Handle magic process-wide effects of stop/continue signals.
 * Unlike the signal actions, these happen immediately at signal-generation
 * time regardless of blocking, ignoring, or handling.  This does the
 * actual continuing for SIGCONT, but not the actual stopping for stop
 * signals.  The process stop is done as a signal action for SIG_DFL.
 */
static void handle_stop_signal(int sig, struct task_struct *p)
{
	struct task_struct *t;

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	if (p->signal->flags & SIGNAL_GROUP_EXIT)
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		/*
		 * The process is in the middle of dying already.
		 */
		return;

	if (sig_kernel_stop(sig)) {
		/*
		 * This is a stop signal.  Remove SIGCONT from all queues.
		 */
		rm_from_queue(sigmask(SIGCONT), &p->signal->shared_pending);
		t = p;
		do {
			rm_from_queue(sigmask(SIGCONT), &t->pending);
			t = next_thread(t);
		} while (t != p);
	} else if (sig == SIGCONT) {
		/*
		 * Remove all stop signals from all queues,
		 * and wake all threads.
		 */
		if (unlikely(p->signal->group_stop_count > 0)) {
			/*
			 * There was a group stop in progress.  We'll
			 * pretend it finished before we got here.  We are
			 * obliged to report it to the parent: if the
			 * SIGSTOP happened "after" this SIGCONT, then it
			 * would have cleared this pending SIGCONT.  If it
			 * happened "before" this SIGCONT, then the parent
			 * got the SIGCHLD about the stop finishing before
			 * the continue happened.  We do the notification
			 * now, and it's as if the stop had finished and
			 * the SIGCHLD was pending on entry to this kill.
			 */
			p->signal->group_stop_count = 0;
			p->signal->flags = SIGNAL_STOP_CONTINUED;
			spin_unlock(&p->sighand->siglock);
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			do_notify_parent_cldstop(p, (p->ptrace & PT_PTRACED), CLD_STOPPED);
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			spin_lock(&p->sighand->siglock);
		}
		rm_from_queue(SIG_KERNEL_STOP_MASK, &p->signal->shared_pending);
		t = p;
		do {
			unsigned int state;
			rm_from_queue(SIG_KERNEL_STOP_MASK, &t->pending);
			
			/*
			 * If there is a handler for SIGCONT, we must make
			 * sure that no thread returns to user mode before
			 * we post the signal, in case it was the only
			 * thread eligible to run the signal handler--then
			 * it must not do anything between resuming and
			 * running the handler.  With the TIF_SIGPENDING
			 * flag set, the thread will pause and acquire the
			 * siglock that we hold now and until we've queued
			 * the pending signal. 
			 *
			 * Wake up the stopped thread _after_ setting
			 * TIF_SIGPENDING
			 */
			state = TASK_STOPPED;
			if (sig_user_defined(t, SIGCONT) && !sigismember(&t->blocked, SIGCONT)) {
				set_tsk_thread_flag(t, TIF_SIGPENDING);
				state |= TASK_INTERRUPTIBLE;
			}
			wake_up_state(t, state);

			t = next_thread(t);
		} while (t != p);

		if (p->signal->flags & SIGNAL_STOP_STOPPED) {
			/*
			 * We were in fact stopped, and are now continued.
			 * Notify the parent with CLD_CONTINUED.
			 */
			p->signal->flags = SIGNAL_STOP_CONTINUED;
			p->signal->group_exit_code = 0;
			spin_unlock(&p->sighand->siglock);
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			do_notify_parent_cldstop(p, (p->ptrace & PT_PTRACED), CLD_CONTINUED);
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			spin_lock(&p->sighand->siglock);
		} else {
			/*
			 * We are not stopped, but there could be a stop
			 * signal in the middle of being processed after
			 * being removed from the queue.  Clear that too.
			 */
			p->signal->flags = 0;
		}
	} else if (sig == SIGKILL) {
		/*
		 * Make sure that any pending stop signal already dequeued
		 * is undone by the wakeup for SIGKILL.
		 */
		p->signal->flags = 0;
	}
}

static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
			struct sigpending *signals)
{
	struct sigqueue * q = NULL;
	int ret = 0;

	/*
	 * fast-pathed signals for kernel-internal things like SIGSTOP
	 * or SIGKILL.
	 */
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	if (info == SEND_SIG_FORCED)
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		goto out_set;

	/* Real-time signals must be queued if sent by sigqueue, or
	   some other real-time mechanism.  It is implementation
	   defined whether kill() does so.  We attempt to do so, on
	   the principle of least surprise, but since kill is not
	   allowed to fail with EAGAIN when low on memory we just
	   make sure at least one signal gets delivered and don't
	   pass on the info struct.  */

	q = __sigqueue_alloc(t, GFP_ATOMIC, (sig < SIGRTMIN &&
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					     (is_si_special(info) ||
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					      info->si_code >= 0)));
	if (q) {
		list_add_tail(&q->list, &signals->list);
		switch ((unsigned long) info) {
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		case (unsigned long) SEND_SIG_NOINFO:
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			q->info.si_signo = sig;
			q->info.si_errno = 0;
			q->info.si_code = SI_USER;
			q->info.si_pid = current->pid;
			q->info.si_uid = current->uid;
			break;
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		case (unsigned long) SEND_SIG_PRIV:
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			q->info.si_signo = sig;
			q->info.si_errno = 0;
			q->info.si_code = SI_KERNEL;
			q->info.si_pid = 0;
			q->info.si_uid = 0;
			break;
		default:
			copy_siginfo(&q->info, info);
			break;
		}
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	} else if (!is_si_special(info)) {
		if (sig >= SIGRTMIN && info->si_code != SI_USER)
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		/*
		 * Queue overflow, abort.  We may abort if the signal was rt
		 * and sent by user using something other than kill().
		 */
			return -EAGAIN;
	}

out_set:
	sigaddset(&signals->signal, sig);
	return ret;
}

#define LEGACY_QUEUE(sigptr, sig) \
	(((sig) < SIGRTMIN) && sigismember(&(sigptr)->signal, (sig)))


static int
specific_send_sig_info(int sig, struct siginfo *info, struct task_struct *t)
{
	int ret = 0;

	if (!irqs_disabled())
		BUG();
	assert_spin_locked(&t->sighand->siglock);

	/* Short-circuit ignored signals.  */
	if (sig_ignored(t, sig))
		goto out;

	/* Support queueing exactly one non-rt signal, so that we
	   can get more detailed information about the cause of
	   the signal. */
	if (LEGACY_QUEUE(&t->pending, sig))
		goto out;

	ret = send_signal(sig, info, t, &t->pending);
	if (!ret && !sigismember(&t->blocked, sig))
		signal_wake_up(t, sig == SIGKILL);
out:
	return ret;
}

/*
 * Force a signal that the process can't ignore: if necessary
 * we unblock the signal and change any SIG_IGN to SIG_DFL.
 */

int
force_sig_info(int sig, struct siginfo *info, struct task_struct *t)
{
	unsigned long int flags;
	int ret;

	spin_lock_irqsave(&t->sighand->siglock, flags);
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	if (t->sighand->action[sig-1].sa.sa_handler == SIG_IGN) {
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		t->sighand->action[sig-1].sa.sa_handler = SIG_DFL;
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	}
	if (sigismember(&t->blocked, sig)) {
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		sigdelset(&t->blocked, sig);
	}
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	recalc_sigpending_tsk(t);
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	ret = specific_send_sig_info(sig, info, t);
	spin_unlock_irqrestore(&t->sighand->siglock, flags);

	return ret;
}

void
force_sig_specific(int sig, struct task_struct *t)
{
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	force_sig_info(sig, SEND_SIG_FORCED, t);
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}

/*
 * Test if P wants to take SIG.  After we've checked all threads with this,
 * it's equivalent to finding no threads not blocking SIG.  Any threads not
 * blocking SIG were ruled out because they are not running and already
 * have pending signals.  Such threads will dequeue from the shared queue
 * as soon as they're available, so putting the signal on the shared queue
 * will be equivalent to sending it to one such thread.
 */
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static inline int wants_signal(int sig, struct task_struct *p)
{
	if (sigismember(&p->blocked, sig))
		return 0;
	if (p->flags & PF_EXITING)
		return 0;
	if (sig == SIGKILL)
		return 1;
	if (p->state & (TASK_STOPPED | TASK_TRACED))
		return 0;
	return task_curr(p) || !signal_pending(p);
}
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static void
__group_complete_signal(int sig, struct task_struct *p)
{
	struct task_struct *t;

	/*
	 * Now find a thread we can wake up to take the signal off the queue.
	 *
	 * If the main thread wants the signal, it gets first crack.
	 * Probably the least surprising to the average bear.
	 */
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	if (wants_signal(sig, p))
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		t = p;
	else if (thread_group_empty(p))
		/*
		 * There is just one thread and it does not need to be woken.
		 * It will dequeue unblocked signals before it runs again.
		 */
		return;
	else {
		/*
		 * Otherwise try to find a suitable thread.
		 */
		t = p->signal->curr_target;
		if (t == NULL)
			/* restart balancing at this thread */
			t = p->signal->curr_target = p;
		BUG_ON(t->tgid != p->tgid);

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		while (!wants_signal(sig, t)) {
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			t = next_thread(t);
			if (t == p->signal->curr_target)
				/*
				 * No thread needs to be woken.
				 * Any eligible threads will see
				 * the signal in the queue soon.
				 */
				return;
		}
		p->signal->curr_target = t;
	}

	/*
	 * Found a killable thread.  If the signal will be fatal,
	 * then start taking the whole group down immediately.
	 */
	if (sig_fatal(p, sig) && !(p->signal->flags & SIGNAL_GROUP_EXIT) &&
	    !sigismember(&t->real_blocked, sig) &&
	    (sig == SIGKILL || !(t->ptrace & PT_PTRACED))) {
		/*
		 * This signal will be fatal to the whole group.
		 */
		if (!sig_kernel_coredump(sig)) {
			/*
			 * Start a group exit and wake everybody up.
			 * This way we don't have other threads
			 * running and doing things after a slower
			 * thread has the fatal signal pending.
			 */
			p->signal->flags = SIGNAL_GROUP_EXIT;
			p->signal->group_exit_code = sig;
			p->signal->group_stop_count = 0;
			t = p;
			do {
				sigaddset(&t->pending.signal, SIGKILL);
				signal_wake_up(t, 1);
				t = next_thread(t);
			} while (t != p);
			return;
		}

		/*
		 * There will be a core dump.  We make all threads other
		 * than the chosen one go into a group stop so that nothing
		 * happens until it gets scheduled, takes the signal off
		 * the shared queue, and does the core dump.  This is a