[PATCH] watch_queue: Annotate struct watch_filter with __counted_by

[Kees Cook]

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct watch_filter.

[1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Siddh Raman Pant <code@xxxxxxxx>
Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
Cc: Qian Cai <cai@xxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 include/linux/watch_queue.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/watch_queue.h b/include/linux/watch_queue.h
index 45cd42f55d49..429c7b6afead 100644
--- a/include/linux/watch_queue.h
+++ b/include/linux/watch_queue.h
@@ -32,7 +32,7 @@ struct watch_filter {
 		DECLARE_BITMAP(type_filter, WATCH_TYPE__NR);
 	};
 	u32			nr_filters;	/* Number of filters */
-	struct watch_type_filter filters[];
+	struct watch_type_filter filters[] __counted_by(nr_filters);
 };
 
 struct watch_queue {
-- 
2.34.1