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 input_mt.

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

Cc: Dmitry Torokhov <[email protected]>
Cc: [email protected]
Signed-off-by: Kees Cook <[email protected]>
---
 include/linux/input/mt.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/input/mt.h b/include/linux/input/mt.h
index 3b8580bd33c1..2cf89a538b18 100644
--- a/include/linux/input/mt.h
+++ b/include/linux/input/mt.h
@@ -47,7 +47,7 @@ struct input_mt {
        unsigned int flags;
        unsigned int frame;
        int *red;
-       struct input_mt_slot slots[];
+       struct input_mt_slot slots[] __counted_by(num_slots);
 };
 
 static inline void input_mt_set_value(struct input_mt_slot *slot,
-- 
2.34.1


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