linux-hardening - [PATCH][next] ASoC: sigmadsp: Add __counted_by for struct sigmadsp_data and use struct

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Message-ID: <ZSRvh1j2MVVhuOUv@work>
Date: Mon, 9 Oct 2023 15:24:23 -0600
From: "Gustavo A. R. Silva" <gustavoars@...nel.org>
To: Lars-Peter Clausen <lars@...afoo.de>,
	Nuno Sá <nuno.sa@...log.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>, Jaroslav Kysela <perex@...ex.cz>,
	Takashi Iwai <tiwai@...e.com>
Cc: alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	linux-hardening@...r.kernel.org
Subject: [PATCH][next] ASoC: sigmadsp: Add __counted_by for struct
 sigmadsp_data and use struct_size()

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).

While there, use struct_size() and size_sub() helpers, instead of the
open-coded version, to calculate the size for the allocation of the
whole flexible structure, including of course, the flexible-array
member.

This code was found with the help of Coccinelle, and audited and
fixed manually.

Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
 sound/soc/codecs/sigmadsp.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/sound/soc/codecs/sigmadsp.c b/sound/soc/codecs/sigmadsp.c
index b93c078a8040..56546e2394ab 100644
--- a/sound/soc/codecs/sigmadsp.c
+++ b/sound/soc/codecs/sigmadsp.c
@@ -43,7 +43,7 @@ struct sigmadsp_data {
 	uint32_t samplerates;
 	unsigned int addr;
 	unsigned int length;
-	uint8_t data[];
+	uint8_t data[] __counted_by(length);
 };
 
 struct sigma_fw_chunk {
@@ -270,7 +270,7 @@ static int sigma_fw_load_data(struct sigmadsp *sigmadsp,
 
 	length -= sizeof(*data_chunk);
 
-	data = kzalloc(sizeof(*data) + length, GFP_KERNEL);
+	data = kzalloc(struct_size(data, data, length), GFP_KERNEL);
 	if (!data)
 		return -ENOMEM;
 
@@ -413,7 +413,8 @@ static int process_sigma_action(struct sigmadsp *sigmadsp,
 		if (len < 3)
 			return -EINVAL;
 
-		data = kzalloc(sizeof(*data) + len - 2, GFP_KERNEL);
+		data = kzalloc(struct_size(data, data, size_sub(len, 2)),
+			       GFP_KERNEL);
 		if (!data)
 			return -ENOMEM;
 
-- 
2.34.1