backend: use fcntl(F_DUPFD_CLOEXEC) instead of dup

This makes sure the CLOEXEC flag is set on the dup'ed FD.

backend/headless/backend.c

@@ -1,6 +1,7 @@
 #define _POSIX_C_SOURCE 200809L
 #include <assert.h>
 #include <drm_fourcc.h>
+#include <fcntl.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <wlr/interfaces/wlr_input_device.h>
@@ -113,19 +114,19 @@ static bool backend_init(struct wlr_headless_backend *backend,
 	backend->renderer = renderer;
 	backend->egl = wlr_gles2_renderer_get_egl(renderer);
 
-	int fd = wlr_renderer_get_drm_fd(renderer);
-	if (fd < 0) {
+	int drm_fd = wlr_renderer_get_drm_fd(renderer);
+	if (drm_fd < 0) {
 		wlr_log(WLR_ERROR, "Failed to get DRM device FD from renderer");
 		return false;
 	}
 
-	fd = dup(fd);
-	if (fd < 0) {
-		wlr_log_errno(WLR_ERROR, "dup failed");
+	drm_fd = fcntl(drm_fd, F_DUPFD_CLOEXEC, 0);
+	if (drm_fd < 0) {
+		wlr_log_errno(WLR_ERROR, "fcntl(F_DUPFD_CLOEXEC) failed");
 		return false;
 	}
 
-	struct wlr_gbm_allocator *alloc = wlr_gbm_allocator_create(fd);
+	struct wlr_gbm_allocator *alloc = wlr_gbm_allocator_create(drm_fd);
 	if (alloc == NULL) {
 		wlr_log(WLR_ERROR, "Failed to create GBM allocator");
 		return false;

backend/wayland/backend.c

@@ -1,4 +1,6 @@
+#define _POSIX_C_SOURCE 200809L
 #include <assert.h>
+#include <fcntl.h>
 #include <limits.h>
 #include <stdint.h>
 #include <stdlib.h>
@@ -335,9 +337,9 @@ struct wlr_backend *wlr_wl_backend_create(struct wl_display *display,
 		goto error_event;
 	}
 
-	drm_fd = dup(drm_fd);
+	drm_fd = fcntl(drm_fd, F_DUPFD_CLOEXEC, 0);
 	if (drm_fd < 0) {
-		wlr_log_errno(WLR_ERROR, "dup failed");
+		wlr_log_errno(WLR_ERROR, "fcntl(F_DUPFD_CLOEXEC) failed");
 		goto error_event;
 	}
 

backend/x11/backend.c

@@ -1,6 +1,6 @@
-#define _POSIX_C_SOURCE 200112L
-
+#define _POSIX_C_SOURCE 200809L
 #include <assert.h>
+#include <fcntl.h>
 #include <limits.h>
 #include <stdbool.h>
 #include <stdio.h>
@@ -490,9 +490,9 @@ struct wlr_backend *wlr_x11_backend_create(struct wl_display *display,
 		return false;
 	}
 
-	drm_fd = dup(drm_fd);
-	if (fd < 0) {
-		wlr_log_errno(WLR_ERROR, "dup failed");
+	drm_fd = fcntl(drm_fd, F_DUPFD_CLOEXEC, 0);
+	if (drm_fd < 0) {
+		wlr_log_errno(WLR_ERROR, "fcntl(F_DUPFD_CLOEXEC) failed");
 		return false;
 	}