Commit 14de5211 authored by Kees Cook's avatar Kees Cook Committed by Herbert Xu
Browse files

crypto: ecc - Remove stack VLA usage 

On the quest to remove all VLAs from the kernel[1], this switches to
a pair of kmalloc regions instead of using the stack. This also moves
the get_random_bytes() after all allocations (and drops the needless
"nbytes" variable).

[1] https://lkml.org/lkml/2018/3/7/621



Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarTudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent b698a9f4

crypto/ecc.c

+17 −6
Original line number Diff line number Diff line
@@ -1025,9 +1025,7 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits, 
{

	int ret = 0;

	struct ecc_point *product, *pk;

	u64 priv[ndigits];

	u64 rand_z[ndigits];

	unsigned int nbytes;

	u64 *priv, *rand_z;

	const struct ecc_curve *curve = ecc_get_curve(curve_id);



	if (!private_key || !public_key || !curve) {
@@ -1035,14 +1033,22 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits, 
		goto out;

	}



	nbytes = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;

	priv = kmalloc_array(ndigits, sizeof(*priv), GFP_KERNEL);

	if (!priv) {

		ret = -ENOMEM;

		goto out;

	}



	get_random_bytes(rand_z, nbytes);

	rand_z = kmalloc_array(ndigits, sizeof(*rand_z), GFP_KERNEL);

	if (!rand_z) {

		ret = -ENOMEM;

		goto kfree_out;

	}



	pk = ecc_alloc_point(ndigits);

	if (!pk) {

		ret = -ENOMEM;

		goto out;

		goto kfree_out;

	}



	product = ecc_alloc_point(ndigits);
@@ -1051,6 +1057,8 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits, 
		goto err_alloc_product;

	}



	get_random_bytes(rand_z, ndigits << ECC_DIGITS_TO_BYTES_SHIFT);



	ecc_swap_digits(public_key, pk->x, ndigits);

	ecc_swap_digits(&public_key[ndigits], pk->y, ndigits);

	ecc_swap_digits(private_key, priv, ndigits);
@@ -1065,6 +1073,9 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits, 
	ecc_free_point(product);

err_alloc_product:

	ecc_free_point(pk);

kfree_out:

	kzfree(priv);

	kzfree(rand_z);

out:

	return ret;

}

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