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Subject[PATCH] Revert "crypto/ecc: Remove stack VLA usage"
This reverts commit 14de52112ee70ca289fa77bf2d9cbc79fd2c811f.

The solution was incomplete and inefficient. This will be fixed
correctly in the next patch.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
crypto/ecc.c | 23 ++++++-----------------
1 file changed, 6 insertions(+), 17 deletions(-)

diff --git a/crypto/ecc.c b/crypto/ecc.c
index 9c066b5ac12d..18f32f2a5e1c 100644
--- a/crypto/ecc.c
+++ b/crypto/ecc.c
@@ -1025,7 +1025,9 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
{
int ret = 0;
struct ecc_point *product, *pk;
- u64 *priv, *rand_z;
+ u64 priv[ndigits];
+ u64 rand_z[ndigits];
+ unsigned int nbytes;
const struct ecc_curve *curve = ecc_get_curve(curve_id);

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

- priv = kmalloc_array(ndigits, sizeof(*priv), GFP_KERNEL);
- if (!priv) {
- ret = -ENOMEM;
- goto out;
- }
+ nbytes = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;

- rand_z = kmalloc_array(ndigits, sizeof(*rand_z), GFP_KERNEL);
- if (!rand_z) {
- ret = -ENOMEM;
- goto kfree_out;
- }
+ get_random_bytes(rand_z, nbytes);

pk = ecc_alloc_point(ndigits);
if (!pk) {
ret = -ENOMEM;
- goto kfree_out;
+ goto out;
}

product = ecc_alloc_point(ndigits);
@@ -1057,8 +1051,6 @@ 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);
@@ -1073,9 +1065,6 @@ 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;
}
--
2.7.4

--
Kees Cook
Pixel Security

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