From 22e3c1c9a1ccc65f02eb873b70178e8e7df74a3f Mon Sep 17 00:00:00 2001
From: claudio <claudio@openbsd.org>
Date: Fri, 11 Mar 2022 10:05:38 +0000
Subject: [PATCH] Revert part of rev 1.293. Using cursig() to deliver masked
 signals to the debugger can cause a loop between the debugger and cursig() if
 the signal is masked. cursig() has no way to know which signal was already
 delivered to the debugger and so it delivers the same signal over and over
 again.

Instead handle traps to masked signals directly in trapsignal. This
is what rev 1.293 was mostly about. If SIGTRAP was masked by the
process breakpoints no longer worked since the signal deliver to
the debugger did not happen. Doing this case in trapsignal solves
both the problem with the loop and the delivery of masked traps.

Problem reported and fix tested by matthieu@
OK kettenis@ mpi@
---
 sys/kern/kern_sig.c | 43 ++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 38 insertions(+), 5 deletions(-)

diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
index 9109b65847b..f9bd8b74e1b 100644
--- a/sys/kern/kern_sig.c
+++ b/sys/kern/kern_sig.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_sig.c,v 1.294 2022/02/14 11:26:05 claudio Exp $	*/
+/*	$OpenBSD: kern_sig.c,v 1.295 2022/03/11 10:05:38 claudio Exp $	*/
 /*	$NetBSD: kern_sig.c,v 1.54 1996/04/22 01:38:32 christos Exp $	*/
 
 /*
@@ -845,6 +845,41 @@ trapsignal(struct proc *p, int signum, u_long trapno, int code,
 		p->p_sicode = code;
 		p->p_sigval = sigval;
 
+		/*
+		 * If traced, stop if signal is masked, and stay stopped
+		 * until released by the debugger.  If our parent process
+		 * is waiting for us, don't hang as we could deadlock.
+		 */
+		if (((pr->ps_flags & (PS_TRACED | PS_PPWAIT)) == PS_TRACED) &&
+		    signum != SIGKILL && (p->p_sigmask & mask) != 0) {
+			int s;
+
+			pr->ps_xsig = signum;
+
+			single_thread_set(p, SINGLE_SUSPEND, 0);
+
+			SCHED_LOCK(s);
+			proc_stop(p, 1);
+			SCHED_UNLOCK(s);
+
+			single_thread_clear(p, 0);
+
+			/*
+			 * If we are no longer being traced, or the parent
+			 * didn't give us a signal, skip sending the signal.
+			 */
+			if ((pr->ps_flags & PS_TRACED) == 0 ||
+			    pr->ps_xsig == 0) {
+				KERNEL_UNLOCK();
+				return;
+			}
+
+			/* update signal info */
+			signum = pr->ps_xsig;
+			p->p_sisig = signum;
+			mask = sigmask(signum);
+		}
+
 		/*
 		 * Signals like SIGBUS and SIGSEGV should not, when
 		 * generated by the kernel, be ignorable or blockable.
@@ -1217,9 +1252,7 @@ cursig(struct proc *p, struct sigctx *sctx)
 	KASSERT(p == curproc);
 
 	for (;;) {
-		mask = (p->p_siglist | pr->ps_siglist);
-		if (!ISSET(pr->ps_flags, PS_TRACED))
-			mask &= ~p->p_sigmask;
+		mask = SIGPENDING(p);
 		if (pr->ps_flags & PS_PPWAIT)
 			mask &= ~STOPSIGMASK;
 		if (mask == 0)	 	/* no signal to send */
@@ -1924,7 +1957,7 @@ userret(struct proc *p)
 		KERNEL_UNLOCK();
 	}
 
-	if (SIGPENDING(p) != 0 || ISSET(p->p_p->ps_flags, PS_TRACED)) {
+	if (SIGPENDING(p) != 0) {
 		KERNEL_LOCK();
 		while ((signum = cursig(p, &ctx)) != 0)
 			postsig(p, signum, &ctx);
-- 
2.20.1