From 57f22c828ec01e0d92bc8858f61df06b4d81ea5c Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Mon, 11 Jan 2021 03:22:44 +0200
Subject: [PATCH] sigfastblock: do not skip cursig/postsig loop in ast()

Even if sigfastblock block is non-zero, non-blockable signals must be
checked on ast and delivered now.  This also affects debugger ability
to attach, because issignal() also calls ptracestop() if there is
a pending stop for debugee.

Instead of checking for sigfastblock, and either setting PENDING flag
for usermode or doing signal delivery loop, always do the loop after
checking, and then handle PENDING bit. issignal() already does the right
thing for fast-blocked case, allowing only STOPs and SIGKILL delivery to
happen.

Reported by:	Vasily Postnicov <shamaz.mazum@gmail.com>, markj
Reviewed by:	markj
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D28089
---
 sys/kern/subr_trap.c | 26 ++++++++++++--------------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/sys/kern/subr_trap.c b/sys/kern/subr_trap.c
index 0c7e43c40ea2..8981091b50ed 100644
--- a/sys/kern/subr_trap.c
+++ b/sys/kern/subr_trap.c
@@ -204,6 +204,7 @@ ast(struct trapframe *framep)
 	struct thread *td;
 	struct proc *p;
 	int flags, sig;
+	bool resched_sigs;
 
 	td = curthread;
 	p = td->td_proc;
@@ -316,27 +317,24 @@ ast(struct trapframe *framep)
 	if (flags & TDF_NEEDSIGCHK || p->p_pendingcnt > 0 ||
 	    !SIGISEMPTY(p->p_siglist)) {
 		sigfastblock_fetch(td);
-		if ((td->td_pflags & TDP_SIGFASTBLOCK) != 0 &&
-		    td->td_sigblock_val != 0) {
-			sigfastblock_setpend(td, true);
-		} else {
-			PROC_LOCK(p);
-			mtx_lock(&p->p_sigacts->ps_mtx);
-			while ((sig = cursig(td)) != 0) {
-				KASSERT(sig >= 0, ("sig %d", sig));
-				postsig(sig);
-			}
-			mtx_unlock(&p->p_sigacts->ps_mtx);
-			PROC_UNLOCK(p);
+		PROC_LOCK(p);
+		mtx_lock(&p->p_sigacts->ps_mtx);
+		while ((sig = cursig(td)) != 0) {
+			KASSERT(sig >= 0, ("sig %d", sig));
+			postsig(sig);
 		}
+		mtx_unlock(&p->p_sigacts->ps_mtx);
+		PROC_UNLOCK(p);
+		resched_sigs = true;
+	} else {
+		resched_sigs = false;
 	}
 
 	/*
 	 * Handle deferred update of the fast sigblock value, after
 	 * the postsig() loop was performed.
 	 */
-	if (td->td_pflags & TDP_SIGFASTPENDING)
-		sigfastblock_setpend(td, false);
+	sigfastblock_setpend(td, resched_sigs);
 
 #ifdef KTRACE
 	KTRUSERRET(td);