linux-hardening - Re: [PATCH] crypto: Use struct

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Date:   Tue, 17 May 2022 14:26:44 -0700
From:   Kees Cook <keescook@...omium.org>
To:     GUO Zihua <guozihua@...wei.com>
Cc:     keyrings@...r.kernel.org, linux-crypto@...r.kernel.org,
        davem@...emloft.net, dhowells@...hat.com,
        herbert@...dor.apana.org.au, gustavoars@...nel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] crypto: Use struct_size() helper in kmalloc()

On Tue, May 17, 2022 at 04:05:32PM +0800, GUO Zihua wrote:
> Make use of struct_size() heler for structures containing flexible array
> member instead of sizeof() which prevents potential issues as well as
> addressing the following sparse warning:
> 
> crypto/asymmetric_keys/asymmetric_type.c:155:23: warning: using sizeof
> on a flexible structure
> crypto/asymmetric_keys/asymmetric_type.c:247:28: warning: using sizeof
> on a flexible structure
> 
> Reference: https://github.com/KSPP/linux/issues/174
> 
> Signed-off-by: GUO Zihua <guozihua@...wei.com>
> ---
>  crypto/asymmetric_keys/asymmetric_type.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/crypto/asymmetric_keys/asymmetric_type.c b/crypto/asymmetric_keys/asymmetric_type.c
> index 41a2f0eb4ce4..96a99a91bf17 100644
> --- a/crypto/asymmetric_keys/asymmetric_type.c
> +++ b/crypto/asymmetric_keys/asymmetric_type.c
> @@ -152,7 +152,7 @@ struct asymmetric_key_id *asymmetric_key_generate_id(const void *val_1,
>  {
>  	struct asymmetric_key_id *kid;
>  
> -	kid = kmalloc(sizeof(struct asymmetric_key_id) + len_1 + len_2,
> +	kid = kmalloc(struct_size(kid, data, len_1 + len_2),

Please use the size_add() helper for this open-coded add here.

>  		      GFP_KERNEL);
>  	if (!kid)
>  		return ERR_PTR(-ENOMEM);
> @@ -244,7 +244,7 @@ struct asymmetric_key_id *asymmetric_key_hex_to_key_id(const char *id)
>  	if (asciihexlen & 1)
>  		return ERR_PTR(-EINVAL);
>  
> -	match_id = kmalloc(sizeof(struct asymmetric_key_id) + asciihexlen / 2,
> +	match_id = kmalloc(struct_size(match_id, data, asciihexlen / 2),

There is no size_div(), but that's ok here because the denominator is an
constant expression.

>  			   GFP_KERNEL);
>  	if (!match_id)
>  		return ERR_PTR(-ENOMEM);
> -- 
> 2.36.0
> 

-- 
Kees Cook