[PATCH for-4.19 3/3] tools/libxs: Fix CLOEXEC handling in xs_fileno()

[Andrew Cooper <andrew.cooper3@citrix.com>]

xs_fileno() opens a pipe on first use to communicate between the watch thread
and the main thread.  Nothing ever sets CLOEXEC on the file descriptors.

Check for the availability of the pipe2() function with configure.  Despite
starting life as Linux-only, FreeBSD and NetBSD have gained it.

When pipe2() isn't available, try our best with pipe() and set_cloexec().

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Anthony PERARD <anthony@xenproject.org>
CC: Juergen Gross <jgross@suse.com>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Frediano Ziglio <frediano.ziglio@cloud.com>
CC: Oleksii Kurochko <oleksii.kurochko@gmail.com>
---
 tools/config.h.in     |  3 +++
 tools/configure       | 12 ++++++++++++
 tools/configure.ac    |  2 ++
 tools/libs/store/xs.c | 16 +++++++++++++++-
 4 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/tools/config.h.in b/tools/config.h.in
index 0bb2fe08a143..50ad60fcb091 100644
--- a/tools/config.h.in
+++ b/tools/config.h.in
@@ -39,6 +39,9 @@
 /* Define to 1 if you have the <memory.h> header file. */
 #undef HAVE_MEMORY_H
 
+/* Define to 1 if you have the `pipe2' function. */
+#undef HAVE_PIPE2
+
 /* pygrub enabled */
 #undef HAVE_PYGRUB
 
diff --git a/tools/configure b/tools/configure
index 459bfb56520e..a6b43bfc6064 100755
--- a/tools/configure
+++ b/tools/configure
@@ -9751,6 +9751,18 @@ if test "$ax_found" = "0"; then :
 fi
 
 
+for ac_func in pipe2
+do :
+  ac_fn_c_check_func "$LINENO" "pipe2" "ac_cv_func_pipe2"
+if test "x$ac_cv_func_pipe2" = xyes; then :
+  cat >>confdefs.h <<_ACEOF
+#define HAVE_PIPE2 1
+_ACEOF
+
+fi
+done
+
+
 cat >confcache <<\_ACEOF
 # This file is a shell script that caches the results of configure
 # tests run on this system so they can be shared between configure
diff --git a/tools/configure.ac b/tools/configure.ac
index 851887080c5e..ac0fdc4314c4 100644
--- a/tools/configure.ac
+++ b/tools/configure.ac
@@ -543,4 +543,6 @@ AS_IF([test "x$pvshim" = "xy"], [
 
 AX_FIND_HEADER([INCLUDE_ENDIAN_H], [endian.h sys/endian.h])
 
+AC_CHECK_FUNCS([pipe2])
+
 AC_OUTPUT()
diff --git a/tools/libs/store/xs.c b/tools/libs/store/xs.c
index 11a766c50887..27bd20933efd 100644
--- a/tools/libs/store/xs.c
+++ b/tools/libs/store/xs.c
@@ -190,13 +190,27 @@ static bool set_cloexec(int fd)
 	return fcntl(fd, flags | FD_CLOEXEC) >= 0;
 }
 
+static int pipe_cloexec(int fds[2])
+{
+#if HAVE_PIPE2
+	return pipe2(fds, O_CLOEXEC);
+#else
+	if (pipe(fds) < 0)
+		return -1;
+	/* Best effort to set CLOEXEC. Racy. */
+	set_cloexec(fds[0]);
+	set_cloexec(fds[1]);
+	return 0;
+#endif
+}
+
 int xs_fileno(struct xs_handle *h)
 {
 	char c = 0;
 
 	mutex_lock(&h->watch_mutex);
 
-	if ((h->watch_pipe[0] == -1) && (pipe(h->watch_pipe) != -1)) {
+	if ((h->watch_pipe[0] == -1) && (pipe_cloexec(h->watch_pipe) != -1)) {
 		/* Kick things off if the watch list is already non-empty. */
 		if (!XEN_TAILQ_EMPTY(&h->watch_list))
 			while (write(h->watch_pipe[1], &c, 1) != 1)
-- 
2.39.2