linux-kernel - Re: [PATCH v2 2/2] crypto: aead,cipher

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Date: Mon, 15 Apr 2024 15:49:42 -0700
From: Eric Biggers <ebiggers@...nel.org>
To: Hailey Mothershead <hailmo@...zon.com>
Cc: herbert@...dor.apana.org.au, davem@...emloft.net,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] crypto: aead,cipher - zeroize key buffer after use

On Mon, Apr 15, 2024 at 10:19:15PM +0000, Hailey Mothershead wrote:
> I.G 9.7.B for FIPS 140-3 specifies that variables temporarily holding
> cryptographic information should be zeroized once they are no longer
> needed. Accomplish this by using kfree_sensitive for buffers that
> previously held the private key.
> 
> Signed-off-by: Hailey Mothershead <hailmo@...zon.com>
> ---
>  crypto/aead.c   | 3 +--
>  crypto/cipher.c | 3 +--
>  2 files changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/crypto/aead.c b/crypto/aead.c
> index 16991095270d..c4ece86c45bc 100644
> --- a/crypto/aead.c
> +++ b/crypto/aead.c
> @@ -35,8 +35,7 @@ static int setkey_unaligned(struct crypto_aead *tfm, const u8 *key,
>  	alignbuffer = (u8 *)ALIGN((unsigned long)buffer, alignmask + 1);
>  	memcpy(alignbuffer, key, keylen);
>  	ret = crypto_aead_alg(tfm)->setkey(tfm, alignbuffer, keylen);
> -	memset(alignbuffer, 0, keylen);
> -	kfree(buffer);
> +	kfree_sensitive(buffer);
>  	return ret;
>  }
>  
> diff --git a/crypto/cipher.c b/crypto/cipher.c
> index b47141ed4a9f..395f0c2fbb9f 100644
> --- a/crypto/cipher.c
> +++ b/crypto/cipher.c
> @@ -34,8 +34,7 @@ static int setkey_unaligned(struct crypto_cipher *tfm, const u8 *key,
>  	alignbuffer = (u8 *)ALIGN((unsigned long)buffer, alignmask + 1);
>  	memcpy(alignbuffer, key, keylen);
>  	ret = cia->cia_setkey(crypto_cipher_tfm(tfm), alignbuffer, keylen);
> -	memset(alignbuffer, 0, keylen);
> -	kfree(buffer);
> +	kfree_sensitive(buffer);
>  	return ret;

Well, the memset()s that you're removing already did the zeroization.  This
patch seems worthwhile as a code simplification, but please don't characterize
it as a bug fix, because it's not.

- Eric