xref: /src/bin/ksh/trap.c

/*	$NetBSD: trap.c,v 1.14.2.2 2020/04/21 19:37:32 martin Exp $	*/

/*
 * signal handling
 */
#include <sys/cdefs.h>

#ifndef lint
__RCSID("$NetBSD: trap.c,v 1.14.2.2 2020/04/21 19:37:32 martin Exp $");
#endif

#include "sh.h"

/* Table is indexed by signal number
 *
 * The script siglist.sh generates siglist.out, which is a sorted, complete
 * list of signals
 */
Trap sigtraps[SIGNALS+1] = {
	{ .signal = SIGEXIT_, .name = "EXIT", .mess = "Signal 0" },
#include "siglist.out"	/* generated by siglist.sh */
	{ .signal = SIGERR_,  .name = "ERR",  .mess = "Error handler" },
    };

static struct sigaction Sigact_ign, Sigact_trap;

void
inittraps()
{
#ifdef HAVE_SYS_SIGLIST
# ifndef SYS_SIGLIST_DECLARED
	extern char	*sys_siglist[];
# endif
	int	i;

	/* Use system description, if available, for unknown signals... */
	for (i = 0; i < NSIG; i++)
		if (!sigtraps[i].name && sys_siglist[i] && sys_siglist[i][0])
			sigtraps[i].mess = sys_siglist[i];
#endif	/* HAVE_SYS_SIGLIST */

	sigemptyset(&Sigact_ign.sa_mask);
	Sigact_ign.sa_flags = KSH_SA_FLAGS;
	Sigact_ign.sa_handler = SIG_IGN;
	Sigact_trap = Sigact_ign;
	Sigact_trap.sa_handler = trapsig;

	sigtraps[SIGINT].flags |= TF_DFL_INTR | TF_TTY_INTR;
	sigtraps[SIGQUIT].flags |= TF_DFL_INTR | TF_TTY_INTR;
	sigtraps[SIGTERM].flags |= TF_DFL_INTR;/* not fatal for interactive */
	sigtraps[SIGHUP].flags |= TF_FATAL;
	sigtraps[SIGCHLD].flags |= TF_SHELL_USES;

	/* these are always caught so we can clean up any temporary files. */
	setsig(&sigtraps[SIGINT], trapsig, SS_RESTORE_ORIG);
	setsig(&sigtraps[SIGQUIT], trapsig, SS_RESTORE_ORIG);
	setsig(&sigtraps[SIGTERM], trapsig, SS_RESTORE_ORIG);
	setsig(&sigtraps[SIGHUP], trapsig, SS_RESTORE_ORIG);
}

#ifdef KSH
static RETSIGTYPE alarm_catcher ARGS((int sig));

void
alarm_init()
{
	sigtraps[SIGALRM].flags |= TF_SHELL_USES;
	setsig(&sigtraps[SIGALRM], alarm_catcher,
		SS_RESTORE_ORIG|SS_FORCE|SS_SHTRAP);
}

static RETSIGTYPE
alarm_catcher(sig)
	int sig;
{
	int errno_ = errno;

	if (ksh_tmout_state == TMOUT_READING) {
		int left = alarm(0);

		if (left == 0) {
			ksh_tmout_state = TMOUT_LEAVING;
			intrsig = 1;
		} else
			alarm(left);
	}
	errno = errno_;
	return RETSIGVAL;
}
#endif /* KSH */

Trap *
gettrap(name, igncase)
	const char *name;
	int igncase;
{
	int i;
	Trap *p;

	if (digit(*name)) {
		int n;

		if (getn(name, &n) && 0 <= n && n < SIGNALS)
			return &sigtraps[n];
		return NULL;
	}
	for (p = sigtraps, i = SIGNALS+1; --i >= 0; p++)
		if (p->name) {
			if (igncase) {
				if (p->name && (!strcasecmp(p->name, name) ||
				    (strlen(name) > 3 && !strncasecmp("SIG",
				    p->name, 3) &&
				    !strcasecmp(p->name, name + 3))))
					return p;
			} else {
				if (p->name && (!strcmp(p->name, name) ||
				    (strlen(name) > 3 && !strncmp("SIG",
				    p->name, 3) && !strcmp(p->name, name + 3))))
					return p;
			}
		}
	return NULL;
}

/*
 * trap signal handler
 */
RETSIGTYPE
trapsig(i)
	int i;
{
	Trap *p = &sigtraps[i];
	int errno_ = errno;

	trap = p->set = 1;
	if (p->flags & TF_DFL_INTR)
		intrsig = 1;
	if ((p->flags & TF_FATAL) && !p->trap) {
		fatal_trap = 1;
		intrsig = 1;
	}
	if (p->shtrap)
		(*p->shtrap)(i);

	errno = errno_;
	return RETSIGVAL;
}

/* called when we want to allow the user to ^C out of something - won't
 * work if user has trapped SIGINT.
 */
void
intrcheck()
{
	if (intrsig)
		runtraps(TF_DFL_INTR|TF_FATAL);
}

/* called after EINTR to check if a signal with normally causes process
 * termination has been received.
 */
int
fatal_trap_check()
{
	int i;
	Trap *p;

	/* todo: should check if signal is fatal, not the TF_DFL_INTR flag */
	for (p = sigtraps, i = SIGNALS+1; --i >= 0; p++)
		if (p->set && (p->flags & (TF_DFL_INTR|TF_FATAL)))
			/* return value is used as an exit code */
			return 128 + p->signal;
	return 0;
}

/* Returns the signal number of any pending traps: ie, a signal which has
 * occurred for which a trap has been set or for which the TF_DFL_INTR flag
 * is set.
 */
int
trap_pending()
{
	int i;
	Trap *p;

	for (p = sigtraps, i = SIGNALS+1; --i >= 0; p++)
		if (p->set && ((p->trap && p->trap[0])
			       || ((p->flags & (TF_DFL_INTR|TF_FATAL))
				   && !p->trap)))
			return p->signal;
	return 0;
}

/*
 * run any pending traps.  If intr is set, only run traps that
 * can interrupt commands.
 */
void
runtraps(flag)
	int flag;
{
	int i;
	Trap *p;

#ifdef KSH
	if (ksh_tmout_state == TMOUT_LEAVING) {
		ksh_tmout_state = TMOUT_EXECUTING;
		warningf(false, "timed out waiting for input");
		unwind(LEXIT);
	} else
		/* XXX: this means the alarm will have no effect if a trap
		 * is caught after the alarm() was started...not good.
		 */
		ksh_tmout_state = TMOUT_EXECUTING;
#endif /* KSH */
	if (!flag)
		trap = 0;
	if (flag & TF_DFL_INTR)
		intrsig = 0;
	if (flag & TF_FATAL)
		fatal_trap = 0;
	for (p = sigtraps, i = SIGNALS+1; --i >= 0; p++)
		if (p->set && (!flag
			       || ((p->flags & flag) && p->trap == (char *) 0)))
			runtrap(p);
}

void
runtrap(p)
	Trap *p;
{
	int	i = p->signal;
	char	*trapstr = p->trap;
	int	oexstat;
	int	UNINITIALIZED(old_changed);

	p->set = 0;
	if (trapstr == (char *) 0) { /* SIG_DFL */
		if (p->flags & TF_FATAL) {
			/* eg, SIGHUP */
			exstat = 128 + i;
			unwind(LLEAVE);
		}
		if (p->flags & TF_DFL_INTR) {
			/* eg, SIGINT, SIGQUIT, SIGTERM, etc. */
			exstat = 128 + i;
			unwind(LINTR);
		}
		return;
	}
	if (trapstr[0] == '\0') /* SIG_IGN */
		return;
	if (i == SIGEXIT_ || i == SIGERR_) {	/* avoid recursion on these */
		old_changed = p->flags & TF_CHANGED;
		p->flags &= ~TF_CHANGED;
		p->trap = (char *) 0;
	}
	oexstat = exstat;
	/* Note: trapstr is fully parsed before anything is executed, thus
	 * no problem with afree(p->trap) in settrap() while still in use.
	 */
	command(trapstr);
	exstat = oexstat;
	if (i == SIGEXIT_ || i == SIGERR_) {
		if (p->flags & TF_CHANGED)
			/* don't clear TF_CHANGED */
			afree(trapstr, APERM);
		else
			p->trap = trapstr;
		p->flags |= old_changed;
	}
}

/* clear pending traps and reset user's trap handlers; used after fork(2) */
void
cleartraps()
{
	int i;
	Trap *p;

	trap = 0;
	intrsig = 0;
	fatal_trap = 0;
	for (i = SIGNALS+1, p = sigtraps; --i >= 0; p++) {
		p->set = 0;
		if ((p->flags & TF_USER_SET) && (p->trap && p->trap[0]))
			settrap(p, (char *) 0);
	}
}

/* restore signals just before an exec(2) */
void
restoresigs()
{
	int i;
	Trap *p;

	for (i = SIGNALS+1, p = sigtraps; --i >= 0; p++)
		if (p->flags & (TF_EXEC_IGN|TF_EXEC_DFL))
			setsig(p, (p->flags & TF_EXEC_IGN) ? SIG_IGN : SIG_DFL,
				SS_RESTORE_CURR|SS_FORCE);
}

void
settrap(p, s)
	Trap *p;
	char *s;
{
	handler_t f;

	if (p->trap)
		afree(p->trap, APERM);
	p->flags |= TF_CHANGED|TF_USER_SET;
	if (s) {
		p->trap = str_save(s, APERM);
		f = s[0] ? trapsig : SIG_IGN;
	} else {
		p->trap = NULL;
		f = SIG_DFL;
	}
	if ((p->flags & (TF_DFL_INTR|TF_FATAL)) && f == SIG_DFL)
		f = trapsig;
	else if (p->flags & TF_SHELL_USES) {
		if (!(p->flags & TF_ORIG_IGN) || Flag(FTALKING)) {
			/* do what user wants at exec time */
			p->flags &= ~(TF_EXEC_IGN|TF_EXEC_DFL);
			if (f == SIG_IGN)
				p->flags |= TF_EXEC_IGN;
			else
				p->flags |= TF_EXEC_DFL;
		}
		/* assumes handler already set to what shell wants it
		 * (normally trapsig, but could be j_sigchld() or SIG_IGN)
		 */
		return;
	}

	/* todo: should we let user know signal is ignored? how? */
	setsig(p, f, SS_RESTORE_CURR|SS_USER);
}

/* Called by c_print() when writing to a co-process to ensure SIGPIPE won't
 * kill shell (unless user catches it and exits)
 */
int
block_pipe()
{
	int restore_dfl = 0;
	Trap *p = &sigtraps[SIGPIPE];

	if (!(p->flags & (TF_ORIG_IGN|TF_ORIG_DFL))) {
		setsig(p, SIG_IGN, SS_RESTORE_CURR);
		if (p->flags & TF_ORIG_DFL)
			restore_dfl = 1;
	} else if (p->cursig == SIG_DFL) {
		setsig(p, SIG_IGN, SS_RESTORE_CURR);
		restore_dfl = 1; /* restore to SIG_DFL */
	}
	return restore_dfl;
}

/* Called by c_print() to undo whatever block_pipe() did */
void
restore_pipe(restore_dfl)
	int restore_dfl;
{
	if (restore_dfl)
		setsig(&sigtraps[SIGPIPE], SIG_DFL, SS_RESTORE_CURR);
}

/* Set action for a signal.  Action may not be set if original
 * action was SIG_IGN, depending on the value of flags and
 * FTALKING.
 */
int
setsig(p, f, flags)
	Trap *p;
	handler_t f;
	int flags;
{
	struct sigaction sigact;

	if (p->signal == SIGEXIT_ || p->signal == SIGERR_)
		return 1;

	/* First time setting this signal?  If so, get and note the current
	 * setting.
	 */
	if (!(p->flags & (TF_ORIG_IGN|TF_ORIG_DFL))) {
		sigaction(p->signal, &Sigact_ign, &sigact);
		p->flags |= sigact.sa_handler == SIG_IGN ?
					TF_ORIG_IGN : TF_ORIG_DFL;
		p->cursig = SIG_IGN;
	}

	/* Generally, an ignored signal stays ignored, except if
	 *	- the user of an interactive shell wants to change it
	 *	- the shell wants for force a change
	 */
	if ((p->flags & TF_ORIG_IGN) && !(flags & SS_FORCE)
	    && (!(flags & SS_USER) || !Flag(FTALKING)))
		return 0;

	setexecsig(p, flags & SS_RESTORE_MASK);

	/* This is here 'cause there should be a way of clearing shtraps, but
	 * don't know if this is a sane way of doing it.  At the moment,
	 * all users of shtrap are lifetime users (SIGCHLD, SIGALRM, SIGWINCH).
	 */
	if (!(flags & SS_USER))
		p->shtrap = (handler_t) 0;
	if (flags & SS_SHTRAP) {
		p->shtrap = f;
		f = trapsig;
	}

	if (p->cursig != f) {
		p->cursig = f;
		sigemptyset(&sigact.sa_mask);
		sigact.sa_flags = KSH_SA_FLAGS;
		sigact.sa_handler = f;
		sigaction(p->signal, &sigact, (struct sigaction *) 0);
	}

	return 1;
}

/* control what signal is set to before an exec() */
void
setexecsig(p, restore)
	Trap *p;
	int restore;
{
	/* XXX debugging */
	if (!(p->flags & (TF_ORIG_IGN|TF_ORIG_DFL)))
		internal_errorf(1, "setexecsig: unset signal %d(%s)",
			p->signal, p->name);

	/* restore original value for exec'd kids */
	p->flags &= ~(TF_EXEC_IGN|TF_EXEC_DFL);
	switch (restore & SS_RESTORE_MASK) {
	  case SS_RESTORE_CURR: /* leave things as they currently are */
		break;
	  case SS_RESTORE_ORIG:
		p->flags |= p->flags & TF_ORIG_IGN ? TF_EXEC_IGN : TF_EXEC_DFL;
		break;
	  case SS_RESTORE_DFL:
		p->flags |= TF_EXEC_DFL;
		break;
	  case SS_RESTORE_IGN:
		p->flags |= TF_EXEC_IGN;
		break;
	}
}