[PATCH] Revert "crypto/ecc: Remove stack VLA usage"

[Kees Cook]

This reverts commit 14de52112ee70ca289fa77bf2d9cbc79fd2c811f.

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

Signed-off-by: Kees Cook <keesc...@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