Fix invalid uses of wl_array_for_each

[1] and [2] have introduced new wl_array usage in wlroots, but
contains a mistake: wl_array_for_each iterates over pointers to
the wl_array entries, not over entries themselves.

Fix all wl_array_for_each call sites. Name the variables "ptr"
to avoid confusion.

Found via ASan:

    ==148752==ERROR: AddressSanitizer: attempting free on address which was not malloc()-ed: 0x602000214111 in thread T0
        #0 0x7f6ff2235f19 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cpp:127
        #1 0x7f6ff1c04004 in wlr_tablet_destroy ../subprojects/wlroots/types/wlr_tablet_tool.c:24
        #2 0x7f6ff1b8463c in wlr_input_device_destroy ../subprojects/wlroots/types/wlr_input_device.c:51
        #3 0x7f6ff1ab9941 in backend_destroy ../subprojects/wlroots/backend/wayland/backend.c:306
        #4 0x7f6ff1a68323 in wlr_backend_destroy ../subprojects/wlroots/backend/backend.c:57
        #5 0x7f6ff1ab36b4 in multi_backend_destroy ../subprojects/wlroots/backend/multi/backend.c:57
        #6 0x7f6ff1ab417c in handle_display_destroy ../subprojects/wlroots/backend/multi/backend.c:124
        #7 0x7f6ff106184e in wl_display_destroy (/usr/lib/libwayland-server.so.0+0x884e)
        #8 0x55cd1a77c9e5 in server_fini ../sway/server.c:218
        #9 0x55cd1a77893f in main ../sway/main.c:400
        #10 0x7f6ff04bdb24 in __libc_start_main (/usr/lib/libc.so.6+0x27b24)
        #11 0x55cd1a73a7ad in _start (/home/simon/src/sway/build/sway/sway+0x33a7ad)

    0x602000214111 is located 1 bytes inside of 16-byte region [0x602000214110,0x602000214120)
    freed by thread T0 here:
        #0 0x7f6ff2235f19 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cpp:127
        #1 0x7f6ff1c04004 in wlr_tablet_destroy ../subprojects/wlroots/types/wlr_tablet_tool.c:24
        #2 0x7f6ff1b8463c in wlr_input_device_destroy ../subprojects/wlroots/types/wlr_input_device.c:51
        #3 0x7f6ff1ab9941 in backend_destroy ../subprojects/wlroots/backend/wayland/backend.c:306
        #4 0x7f6ff1a68323 in wlr_backend_destroy ../subprojects/wlroots/backend/backend.c:57
        #5 0x7f6ff1ab36b4 in multi_backend_destroy ../subprojects/wlroots/backend/multi/backend.c:57
        #6 0x7f6ff1ab417c in handle_display_destroy ../subprojects/wlroots/backend/multi/backend.c:124
        #7 0x7f6ff106184e in wl_display_destroy (/usr/lib/libwayland-server.so.0+0x884e)

    previously allocated by thread T0 here:
        #0 0x7f6ff2236279 in __interceptor_malloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cpp:145
        #1 0x7f6ff1066d03 in wl_array_add (/usr/lib/libwayland-server.so.0+0xdd03)

[1]: https://github.com/swaywm/wlroots/pull/3002
[2]: https://github.com/swaywm/wlroots/pull/3004

3 files changed, 13 insertions, 11 deletions

diff --git a/backend/libinput/backend.c b/backend/libinput/backend.c
index a9595df2..c7bde4a9 100644
--- a/backend/libinput/backend.c
+++ b/backend/libinput/backend.c
@@ -141,13 +141,13 @@ static void backend_destroy(struct wlr_backend *wlr_backend) {
 	struct wlr_libinput_backend *backend =
 		get_libinput_backend_from_backend(wlr_backend);
 
-	struct wl_list *wlr_devices;
-	wl_array_for_each(wlr_devices, &backend->wlr_device_lists) {
+	struct wl_list **wlr_devices_ptr;
+	wl_array_for_each(wlr_devices_ptr, &backend->wlr_device_lists) {
 		struct wlr_input_device *wlr_dev, *next;
-		wl_list_for_each_safe(wlr_dev, next, wlr_devices, link) {
+		wl_list_for_each_safe(wlr_dev, next, *wlr_devices_ptr, link) {
 			wlr_input_device_destroy(wlr_dev);
 		}
-		free(wlr_devices);
+		free(*wlr_devices_ptr);
 	}
 
 	wlr_backend_finish(wlr_backend);
diff --git a/backend/libinput/events.c b/backend/libinput/events.c
index 1fc8cc09..f149b2f1 100644
--- a/backend/libinput/events.c
+++ b/backend/libinput/events.c
@@ -220,8 +220,9 @@ static void handle_device_removed(struct wlr_libinput_backend *backend,
 		wlr_input_device_destroy(dev);
 	}
 	size_t i = 0;
-	struct wl_list *iter;
-	wl_array_for_each(iter, &backend->wlr_device_lists) {
+	struct wl_list **ptr;
+	wl_array_for_each(ptr, &backend->wlr_device_lists) {
+		struct wl_list *iter = *ptr;
 		if (iter == wlr_devices) {
 			array_remove_at(&backend->wlr_device_lists,
 				i * sizeof(struct wl_list *), sizeof(struct wl_list *));
diff --git a/backend/libinput/tablet_tool.c b/backend/libinput/tablet_tool.c
index 8b143e7f..b0427e5f 100644
--- a/backend/libinput/tablet_tool.c
+++ b/backend/libinput/tablet_tool.c
@@ -48,8 +48,9 @@ static void destroy_tablet(struct wlr_tablet *wlr_tablet) {
 	struct wlr_libinput_tablet *tablet =
 		wl_container_of(wlr_tablet, tablet, wlr_tablet);
 
-	struct wlr_libinput_tablet_tool *tool;
-	wl_array_for_each(tool, &tablet->tools) {
+	struct wlr_libinput_tablet_tool **tool_ptr;
+	wl_array_for_each(tool_ptr, &tablet->tools) {
+		struct wlr_libinput_tablet_tool *tool = *tool_ptr;
 		if (--tool->pad_refs == 0) {
 			destroy_tool(tool);
 		}
@@ -151,9 +152,9 @@ static void ensure_tool_reference(struct wlr_libinput_tablet_tool *tool,
 	struct wlr_libinput_tablet *tablet =
 		wl_container_of(wlr_dev, tablet, wlr_tablet);
 
-	struct wlr_libinput_tablet_tool *iter;
-	wl_array_for_each(iter, &tablet->tools) {
-		if (iter == tool) { // We already have a ref
+	struct wlr_libinput_tablet_tool **tool_ptr;
+	wl_array_for_each(tool_ptr, &tablet->tools) {
+		if (*tool_ptr == tool) { // We already have a ref
 			// XXX: We *could* optimize the tool to the front of
 			// the list here, since we will probably get the next
 			// couple of events from the same tool.