linux-hardening - [PATCH] reset: Annotate struct reset_control_array with __counted

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Message-Id: <20230922175229.work.838-kees@kernel.org>
Date: Fri, 22 Sep 2023 10:52:29 -0700
From: Kees Cook <keescook@...omium.org>
To: Philipp Zabel <p.zabel@...gutronix.de>
Cc: Kees Cook <keescook@...omium.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] reset: Annotate struct reset_control_array 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 reset_control_array.
Additionally, since the element count member must be set before accessing
the annotated flexible array member, move its initialization earlier.

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

Cc: Philipp Zabel <p.zabel@...gutronix.de>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/reset/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/reset/core.c b/drivers/reset/core.c
index f0a076e94118..7ece6a8e9858 100644
--- a/drivers/reset/core.c
+++ b/drivers/reset/core.c
@@ -60,7 +60,7 @@ struct reset_control {
 struct reset_control_array {
 	struct reset_control base;
 	unsigned int num_rstcs;
-	struct reset_control *rstc[];
+	struct reset_control *rstc[] __counted_by(num_rstcs);
 };
 
 static const char *rcdev_name(struct reset_controller_dev *rcdev)
@@ -1185,6 +1185,7 @@ of_reset_control_array_get(struct device_node *np, bool shared, bool optional,
 	resets = kzalloc(struct_size(resets, rstc, num), GFP_KERNEL);
 	if (!resets)
 		return ERR_PTR(-ENOMEM);
+	resets->num_rstcs = num;
 
 	for (i = 0; i < num; i++) {
 		rstc = __of_reset_control_get(np, NULL, i, shared, optional,
@@ -1193,7 +1194,6 @@ of_reset_control_array_get(struct device_node *np, bool shared, bool optional,
 			goto err_rst;
 		resets->rstc[i] = rstc;
 	}
-	resets->num_rstcs = num;
 	resets->base.array = true;
 
 	return &resets->base;
-- 
2.34.1