Avoid the user-visible effect of setting SA_NOCLDWAIT when the

SIGCHLD handler is SIG_IGN. This is a reimplementation of the
problematic revision 1.131 of kern_exit.c. To avoid accessing process
UPAGES, we set a new procsig flag when the SIGCHLD handler is SIG_IGN
and use that instead.

sys/kern/kern_exit.c

@@ -368,10 +368,10 @@ exit1(td, rv)
 
 	/*
 	 * Notify parent that we're gone.  If parent has the PS_NOCLDWAIT
-	 * flag set, notify process 1 instead (and hope it will handle
-	 * this situation).
+	 * flag set, or if the handler is set to SIG_IGN, notify process
+	 * 1 instead (and hope it will handle this situation).
 	 */
-	if (p->p_pptr->p_procsig->ps_flag & PS_NOCLDWAIT) {
+	if (p->p_pptr->p_procsig->ps_flag & (PS_NOCLDWAIT | PS_CLDSIGIGN)) {
 		struct proc *pp = p->p_pptr;
 		PROC_UNLOCK(pp);
 		proc_reparent(p, initproc);

sys/kern/kern_sig.c

@@ -304,8 +304,7 @@ do_sigaction(p, sig, act, oact, old)
 				p->p_procsig->ps_flag |= PS_NOCLDSTOP;
 			else
 				p->p_procsig->ps_flag &= ~PS_NOCLDSTOP;
-			if ((act->sa_flags & SA_NOCLDWAIT) ||
-			    ps->ps_sigact[_SIG_IDX(SIGCHLD)] == SIG_IGN) {
+			if (act->sa_flags & SA_NOCLDWAIT) {
 				/*
 				 * Paranoia: since SA_NOCLDWAIT is implemented
 				 * by reparenting the dying child to PID 1 (and
@@ -318,6 +317,10 @@ do_sigaction(p, sig, act, oact, old)
 					p->p_procsig->ps_flag |= PS_NOCLDWAIT;
 			} else
 				p->p_procsig->ps_flag &= ~PS_NOCLDWAIT;
+			if (ps->ps_sigact[_SIG_IDX(SIGCHLD)] == SIG_IGN)
+				p->p_procsig->ps_flag |= PS_CLDSIGIGN;
+			else
+				p->p_procsig->ps_flag &= ~PS_CLDSIGIGN;
 		}
 		/*
 		 * Set bit in p_sigignore for signals that are set to SIG_IGN,
@@ -499,7 +502,7 @@ execsigs(p)
 	/*
 	 * Reset no zombies if child dies flag as Solaris does.
 	 */
-	p->p_procsig->ps_flag &= ~PS_NOCLDWAIT;
+	p->p_procsig->ps_flag &= ~(PS_NOCLDWAIT | PS_CLDSIGIGN);
 	if (ps->ps_sigact[_SIG_IDX(SIGCHLD)] == SIG_IGN)
 		ps->ps_sigact[_SIG_IDX(SIGCHLD)] = SIG_DFL;
 	PROC_UNLOCK(p);

sys/sys/proc.h

@@ -106,6 +106,7 @@ struct procsig {
 
 #define	PS_NOCLDWAIT	0x0001	/* No zombies if child dies */
 #define	PS_NOCLDSTOP	0x0002	/* No SIGCHLD when children stop. */
+#define	PS_CLDSIGIGN	0x0004	/* The SIGCHLD handler is SIG_IGN. */
 
 /*
  * pargs, used to hold a copy of the command line, if it had a sane length.