Re: [PATCH] crypto/ecc: Remove stack VLA usage

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Hi, Kees,

On 03/07/2018 11:56 PM, Kees Cook wrote:
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: Kees Cook <keescook@xxxxxxxxxxxx>
---
  crypto/ecc.c | 23 +++++++++++++++++------
  1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/crypto/ecc.c b/crypto/ecc.c
index 18f32f2a5e1c..5bfa63603da0 100644
--- a/crypto/ecc.c
+++ b/crypto/ecc.c
@@ -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:
+	kfree(priv);

I think we should use kzfree here.

+	kfree(rand_z);

Probably here too. Looks like there are few intermediate buffers in ecc
that should be zeroized as well.

Best,
ta
  out:
  	return ret;
  }




[Index of Archives]     [Kernel]     [Gnu Classpath]     [Gnu Crypto]     [DM Crypt]     [Netfilter]     [Bugtraq]

  Powered by Linux