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Date: Mon, 9 Oct 2023 15:03:56 -0700
From: Kees Cook <keescook@...omium.org>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: 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>, alsa-devel@...a-project.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] ASoC: sigmadsp: Add __counted_by for struct
 sigmadsp_data and use struct_size()

On Mon, Oct 09, 2023 at 03:24:23PM -0600, Gustavo A. R. Silva wrote:
> 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);

Since len was just size-checked before the alloc, size_sub() is a bit of
overkill, but it's not technically wrong. :P

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook

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