[PATCH] ima: dynamically allocate shash_desc

[Mimi Zohar]

On Mon, 2019-06-17 at 13:20 +0200, Arnd Bergmann wrote:
> On 32-bit ARM, we get a warning about excessive stack usage when
> building with clang.
> 
> security/integrity/ima/ima_crypto.c:504:5: error: stack frame size
> of 1152 bytes in function 'ima_calc_field_array_hash' [-Werror,-
> Wframe-larger-than=]

I'm definitely not seeing this.  Is this problem a result of non
upstreamed patches?  For sha1, currently the only possible hash
algorithm, I'm seeing 664.

Mimi

> 
> Using kmalloc to get the descriptor reduces this to 320 bytes.
> 
> Signed-off-by: Arnd Bergmann <arnd at arndb.de>
> ---
>  security/integrity/ima/ima_crypto.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/security/integrity/ima/ima_crypto.c b/security/integrity/ima/ima_crypto.c
> index d4c7b8e1b083..8a66bab4c435 100644
> --- a/security/integrity/ima/ima_crypto.c
> +++ b/security/integrity/ima/ima_crypto.c
> @@ -461,16 +461,21 @@ static int ima_calc_field_array_hash_tfm(struct ima_field_data *field_data,
>  					 struct ima_digest_data *hash,
>  					 struct crypto_shash *tfm)
>  {
> -	SHASH_DESC_ON_STACK(shash, tfm);
> +	struct shash_desc *shash;
>  	int rc, i;
>  
> +	shash = kmalloc(sizeof(struct shash_desc) + crypto_shash_descsize(tfm),
> +			GFP_KERNEL);
> +	if (!shash)
> +		return -ENOMEM;
> +
>  	shash->tfm = tfm;
>  
>  	hash->length = crypto_shash_digestsize(tfm);
>  
>  	rc = crypto_shash_init(shash);
>  	if (rc != 0)
> -		return rc;
> +		goto out;
>  
>  	for (i = 0; i < num_fields; i++) {
>  		u8 buffer[IMA_EVENT_NAME_LEN_MAX + 1] = { 0 };
> @@ -497,7 +502,8 @@ static int ima_calc_field_array_hash_tfm(struct ima_field_data *field_data,
>  
>  	if (!rc)
>  		rc = crypto_shash_final(shash, hash->digest);
> -
> +out:
> +	kfree(shash);
>  	return rc;
>  }
>