wet_process: Use fdstr when executing clients

This doesn't actually stop us from calling setenv() in between fork()
and exec() when starting clients, but gets us closer to Xwayland's safe
implementation by reusing one of the helpers it added.

Signed-off-by: Daniel Stone <daniels@collabora.com>

compositor/main.c

@@ -51,6 +51,7 @@
 #include <libweston/libweston.h>
 #include "shared/os-compatibility.h"
 #include "shared/helpers.h"
+#include "shared/process-util.h"
 #include "shared/string-helpers.h"
 #include "git-version.h"
 #include <libweston/version.h>
@@ -368,10 +369,8 @@ sigchld_handler(int signal_number, void *data)
 }
 
 static void
-child_client_exec(int sockfd, const char *path)
+child_client_exec(struct fdstr *wayland_socket, const char *path)
 {
-	int clientfd;
-	char s[32];
 	sigset_t allsigs;
 
 	/* do not give our signal mask to the new process */
@@ -384,16 +383,7 @@ child_client_exec(int sockfd, const char *path)
 		return;
 	}
 
-	/* SOCK_CLOEXEC closes both ends, so we dup the fd to get a
-	 * non-CLOEXEC fd to pass through exec. */
-	clientfd = dup(sockfd);
-	if (clientfd == -1) {
-		weston_log("compositor: dup failed: %s\n", strerror(errno));
-		return;
-	}
-
-	snprintf(s, sizeof s, "%d", clientfd);
-	setenv("WAYLAND_SOCKET", s, 1);
+	setenv("WAYLAND_SOCKET", wayland_socket->str1, 1);
 
 	if (execl(path, path, NULL) < 0)
 		weston_log("compositor: executing '%s' failed: %s\n",
@@ -406,18 +396,21 @@ weston_client_launch(struct weston_compositor *compositor,
 		     const char *path,
 		     weston_process_cleanup_func_t cleanup)
 {
-	int sv[2];
-	pid_t pid;
 	struct wl_client *client = NULL;
+	struct fdstr wayland_socket;
+	pid_t pid;
+	bool ret;
 
 	weston_log("launching '%s'\n", path);
 
-	if (os_socketpair_cloexec(AF_UNIX, SOCK_STREAM, 0, sv) < 0) {
+	if (os_socketpair_cloexec(AF_UNIX, SOCK_STREAM, 0,
+				  wayland_socket.fds) < 0) {
 		weston_log("weston_client_launch: "
 			   "socketpair failed while launching '%s': %s\n",
 			   path, strerror(errno));
 		return NULL;
 	}
+	fdstr_update_str1(&wayland_socket);
 
 	pid = fork();
 	switch (pid) {
@@ -429,14 +422,23 @@ weston_client_launch(struct weston_compositor *compositor,
 		 * will cleanly shut down when the child exits.
 		 */
 		setsid();
-		child_client_exec(sv[1], path);
+
+		ret = fdstr_clear_cloexec_fd1(&wayland_socket);
+		if (!ret) {
+			weston_log("compositor: clearing CLOEXEC failed: %s\n",
+				   strerror(errno));
+			_exit(EXIT_FAILURE);
+		}
+
+		child_client_exec(&wayland_socket, path);
 		_exit(-1);
 
 	default:
-		close(sv[1]);
-		client = wl_client_create(compositor->wl_display, sv[0]);
+		close(wayland_socket.fds[1]);
+		client = wl_client_create(compositor->wl_display,
+					  wayland_socket.fds[0]);
 		if (!client) {
-			close(sv[0]);
+			close(wayland_socket.fds[0]);
 			weston_log("weston_client_launch: "
 				"wl_client_create failed while launching '%s'.\n",
 				path);
@@ -449,8 +451,7 @@ weston_client_launch(struct weston_compositor *compositor,
 		break;
 
 	case -1:
-		close(sv[0]);
-		close(sv[1]);
+		fdstr_close_all(&wayland_socket);
 		weston_log("weston_client_launch: "
 			   "fork failed while launching '%s': %s\n", path,
 			   strerror(errno));