Re: [PATCH v3 1/2] crypto: ecdh - Pass private key in proper byte order to check valid key

[Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>]

On Thu, Apr 18, 2024 at 11:24:44AM -0400, Stefan Berger wrote:
> ecc_is_key_valid expects a key with the most significant digit in the last
> entry of the digit array. Currently ecdh_set_secret passes a reversed key
> to ecc_is_key_valid that then passes the rather simple test checking
> whether the private key is in range [2, n-3]. For all current ecdh-
> supported curves (NIST P192/256/384) the 'n' parameter is a rather large
> number, therefore easily passing this test.
> 
> Throughout the ecdh and ecc codebase the variable 'priv' is used for a
> private_key holding the bytes in proper byte order. Therefore, introduce
> priv in ecdh_set_secret and copy the bytes from ctx->private_key into
> priv in proper byte order by using ecc_swap_digits. Pass priv to
> ecc_is_valid_key.
> 
> Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
> Cc: Salvatore Benedetto <salvatore.benedetto@xxxxxxxxx>
> Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
> Acked-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
> ---
>  crypto/ecdh.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/crypto/ecdh.c b/crypto/ecdh.c
> index 3049f147e011..c02c9a2b9682 100644
> --- a/crypto/ecdh.c
> +++ b/crypto/ecdh.c
> @@ -27,7 +27,9 @@ static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
>  			   unsigned int len)
>  {
>  	struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
> +	u64 priv[ECC_MAX_DIGITS];
>  	struct ecdh params;
> +	int ret = 0;
>  
>  	if (crypto_ecdh_decode_key(buf, len, &params) < 0 ||
>  	    params.key_size > sizeof(u64) * ctx->ndigits)
> @@ -40,13 +42,16 @@ static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
>  				       ctx->private_key);
>  
>  	memcpy(ctx->private_key, params.key, params.key_size);
> +	ecc_swap_digits(ctx->private_key, priv, ctx->ndigits);

These functions need to use our sparse marking mechanism correctly
to prevent future occurences of such errors.  They should not be
passing around void * pointers or worse, treating u64 * arrays as
big-endian.

Cheers,
-- 
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt