Use the self-pipe trick to fix the signal handling bug.

Closes:#850079.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

4 files changed, 111 insertions, 6 deletions

diff --git a/debian/changelog b/debian/changelog
index a41b500..f404585 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,6 +1,8 @@
 vtwm (5.4.7-5~) unstable; urgency=medium
 
-  * 
+  Bugfix:
+  * Use the self-pipe trick to fix the signal handling bug, instead
+    of sigprocmask.  Closes:#850079.
 
  -- Ian Jackson <ijackson@chiark.greenend.org.uk>  Tue, 03 Jan 2017 23:19:00 +0000
 
diff --git a/events.c b/events.c
index 28e1e29..beeb2e8 100644
--- a/events.c
+++ b/events.c
@@ -38,6 +38,9 @@
 
 #include <stdio.h>
 #include <string.h>
+#include <signal.h>
+#include <poll.h>
+#include <errno.h>
 #include "twm.h"
 #include <X11/Xatom.h>
 #include "add_window.h"
@@ -63,6 +66,9 @@
 #include <sys/types.h>	/* RAISEDELAY */
 #include <unistd.h>
 #endif
+#include <unistd.h>
+#include <assert.h>
+#include <sys/fcntl.h>
 
 extern void IconDown();
 /* djhjr - 4/26/99 */
@@ -362,6 +368,68 @@ Bool DispatchEvent ()
 
 /***********************************************************************
  *
+ *  Procedures:
+ *      HandleSignal   use instead of signal
+ *
+ ***********************************************************************
+ */
+
+#define HANDLE_SIG_MAX 256 /* increase means changing type written to pipe */
+
+static SigProc signaltable[HANDLE_SIG_MAX];
+static int sigselfpipe[2] = { -1, -1 };
+
+static void
+SelfPipeHandler(sig)
+	int sig;
+{
+	unsigned char sigchar = sig;
+	int esave;
+
+	esave = errno;
+	write(sigselfpipe[1], &sigchar, 1);
+	errno = esave;
+}
+
+void
+HandleSignal(sig, func)
+	int sig;
+	SigProc func;
+{
+	struct sigaction sa;
+	int r, i;
+
+	if (sigselfpipe[0] == -1) {
+		r = pipe(sigselfpipe);
+		if (r) { perror("pipe for signals"); exit(-1); }
+		for (i = 0; i < 2; i++) {
+			r = fcntl(sigselfpipe[i], F_GETFL);
+			if (r<0) { perror("fcntl get for pipe"); exit(-1); }
+			r |= O_NONBLOCK;
+			r = fcntl(sigselfpipe[i], F_SETFL, r);
+			if (r<0) { perror("fcntl get for pipe"); exit(-1); }
+		}
+	}
+
+	assert(sig < HANDLE_SIG_MAX);
+
+	r = sigaction(sig, NULL, &sa);
+	if (r) { perror("sigaction get"); exit(-1); }
+
+	if (sa.sa_handler != SIG_DFL)
+		return;
+
+	signaltable[sig] = func;
+	memset(&sa, 0, sizeof(sa));
+	sa.sa_handler = SelfPipeHandler;
+	sigemptyset(&sa.sa_mask);
+	sa.sa_flags = SA_RESTART;
+	r = sigaction(sig, &sa, NULL);
+	if (r) { perror("sigaction set"); exit(-1); }
+}
+
+/***********************************************************************
+ *
  *  Procedure:
  *	HandleEvents - handle X events
  *
@@ -371,6 +439,14 @@ Bool DispatchEvent ()
 void
 HandleEvents()
 {
+	struct pollfd pfds[2];
+	pfds[0].fd = ConnectionNumber(dpy);
+	pfds[0].events = POLLIN|POLLPRI;
+	pfds[1].fd = sigselfpipe[0];
+	pfds[1].events = POLLIN|POLLPRI;
+	sigset_t emptyset;
+	sigemptyset(&emptyset);
+
 	while (TRUE)
 	{
 	if (enter_flag && !QLength(dpy)) {
@@ -384,7 +460,32 @@ HandleEvents()
 	    InstallWindowColormaps(ColormapNotify, (TwmWindow *) NULL);
 	}
 	WindowMoved = FALSE;
-	XNextEvent(dpy, &Event);
+	while (!XCheckMaskEvent(dpy, -1 /* wot no AllEventMask */, &Event)) {
+		int r;
+		unsigned char signum;
+		r = poll(pfds, 2, -1);
+		if (r<0 && errno!=EINTR) {
+			perror("vtwm: poll failed");
+			exit(-1);
+		}
+		for (;;) {
+			r = read(sigselfpipe[0], &signum, 1);
+			if (r < 0) {
+				if (errno == EINTR) continue;
+				if (errno == EAGAIN) break;
+				if (errno == EWOULDBLOCK) break;
+				perror("vtwm: read signal self-pipe");
+				exit(-1);
+			}
+			if (!r) {
+				fputs("signal self-pipe read EOF!",stderr);
+				exit(-1);
+			}
+			assert(signum < HANDLE_SIG_MAX);
+			assert(signaltable[signum]);
+			signaltable[signum](signum);
+		}
+	}
 	(void) DispatchEvent ();
 	}
 }
diff --git a/events.h b/events.h
index 8d42304..498ef1e 100644
--- a/events.h
+++ b/events.h
@@ -77,6 +77,8 @@ extern void InstallWindowColormaps();
 extern void RedoDoorName(); /* djhjr - 2/28/99 */
 extern void RedoListWindow(); /* djhjr - 3/1/99 */
 
+extern void HandleSignal();
+
 extern event_proc EventHandler[];
 extern Window DragWindow;
 extern int origDragX;
diff --git a/twm.c b/twm.c
index 1402eee..54b8957 100644
--- a/twm.c
+++ b/twm.c
@@ -258,13 +258,13 @@ main(argc, argv, environ)
 /* djhjr - 6/22/01 */
 #ifndef NO_SOUND_SUPPORT
 #define sounddonehandler(sig) \
-    if (signal (sig, SIG_IGN) != SIG_IGN) (void) signal (sig, PlaySoundDone)
+    HandleSignal (sig, PlaySoundDone)
 #else
 #define sounddonehandler(sig) \
-    if (signal (sig, SIG_IGN) != SIG_IGN) (void) signal (sig, Done)
+    HandleSignal (sig, Done)
 #endif
 #define donehandler(sig) \
-    if (signal (sig, SIG_IGN) != SIG_IGN) (void) signal (sig, Done)
+    HandleSignal (sig, Done)
 
     sounddonehandler (SIGINT);
     sounddonehandler (SIGHUP);
@@ -282,7 +282,7 @@ main(argc, argv, environ)
 #undef donehandler
 
     /* djhjr - 7/31/98 */
-    signal (SIGUSR1, QueueRestartVtwm);
+    HandleSignal (SIGUSR1, QueueRestartVtwm);
 
     Home = getenv("HOME");
     if (Home == NULL)