From 6c6072ba8b079e6f5caa38b011a6f4570c14ed38 Mon Sep 17 00:00:00 2001
From: Darren Tucker <dtucker@dtucker.net>
Date: Fri, 1 May 2020 15:09:26 +1000
Subject: See if SA_RESTART signals will interrupt select().

On some platforms (at least older HP-UXes such as 11.11, possibly others)
setting SA_RESTART on signal handers will cause it to not interrupt
select(), at least for calls that do not specify a timeout.  Try to
detect this and if found, don't use SA_RESTART.

POSIX says "If SA_RESTART has been set for the interrupting signal, it
is implementation-dependent whether select() restarts or returns with
[EINTR]" so this behaviour is within spec.
---
 configure.ac | 37 +++++++++++++++++++++++++++++++++++++
 misc.c       |  2 ++
 2 files changed, 39 insertions(+)

diff --git a/configure.ac b/configure.ac
index 8adfcb347..e696ac751 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2500,6 +2500,43 @@ static void sighandler(int sig) { _exit(1); }
 	)
 fi
 
+AC_MSG_CHECKING([if SA_RESTARTed signals interrupt select()])
+AC_RUN_IFELSE(
+	[AC_LANG_PROGRAM([[
+#ifdef HAVE_SYS_SELECT
+# include <sys/select.h>
+#endif
+#include <sys/types.h>
+#include <sys/time.h>
+#include <stdlib.h>
+#include <signal.h>
+static void sighandler(int sig) { }
+		]], [[
+	int r;
+	pid_t pid;
+	struct sigaction sa;
+
+	sa.sa_handler = sighandler;
+	sa.sa_flags = SA_RESTART;
+	(void)sigaction(SIGTERM, &sa, NULL);
+	if ((pid = fork()) == 0) { /* child */
+		sleep(1);
+		kill(getppid(), SIGTERM);
+		sleep(1);
+		kill(getppid(), SIGKILL);
+		exit(0);
+	} else { /* parent */
+		r = select(0, NULL, NULL, NULL, NULL);
+	}
+	exit(r == -1 ? 0 : 1);
+	]])],
+	[AC_MSG_RESULT([yes])],
+	[AC_MSG_RESULT([no])
+	 AC_DEFINE([NO_SA_RESTART], [1],
+	    [SA_RESTARTed signals do no interrupt select])],
+	[AC_MSG_WARN([cross compiling: assuming yes])]
+)
+
 AC_CHECK_FUNCS([getpgrp],[
 	AC_MSG_CHECKING([if getpgrp accepts zero args])
 	AC_COMPILE_IFELSE(
diff --git a/misc.c b/misc.c
index 506507226..554ceb0b1 100644
--- a/misc.c
+++ b/misc.c
@@ -2258,8 +2258,10 @@ ssh_signal(int signum, sshsig_t handler)
 	memset(&sa, 0, sizeof(sa));
 	sa.sa_handler = handler;
 	sigfillset(&sa.sa_mask);
+#if defined(SA_RESTART) && !defined(NO_SA_RESTART)
 	if (signum != SIGALRM)
 		sa.sa_flags = SA_RESTART;
+#endif
 	if (sigaction(signum, &sa, &osa) == -1) {
 		debug3("sigaction(%s): %s", strsignal(signum), strerror(errno));
 		return SIG_ERR;
-- 
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