[PATCH] Input: Annotate struct ff_device 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 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 ff_device.

Cc: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
Cc: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx>
Cc: linux-input@xxxxxxxxxxxxxxx
Cc: linux-hardening@xxxxxxxxxxxxxxx
Link: https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci [1]
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 include/linux/input.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/input.h b/include/linux/input.h
index 49790c1bd2c4..de6503c0edb8 100644
--- a/include/linux/input.h
+++ b/include/linux/input.h
@@ -562,7 +562,7 @@ struct ff_device {
 
 	int max_effects;
 	struct ff_effect *effects;
-	struct file *effect_owners[];
+	struct file *effect_owners[] __counted_by(max_effects);
 };
 
 int input_ff_create(struct input_dev *dev, unsigned int max_effects);
-- 
2.34.1