linux-hardening - [PATCH] input: mt: Annotate struct input_mt with __counted

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Date: Fri, 22 Sep 2023 10:50:37 -0700
From: Kees Cook <keescook@...omium.org>
To: Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: Kees Cook <keescook@...omium.org>,
	linux-input@...r.kernel.org,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Tom Rix <trix@...hat.com>,
	linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev,
	linux-hardening@...r.kernel.org
Subject: [PATCH] input: mt: Annotate struct input_mt with __counted_by

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 <dmitry.torokhov@...il.com>
Cc: linux-input@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 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