Hi Tycho,
On Mon, Apr 23, 2018 at 07:03:19PM -0600, Tycho Andersen wrote:
> We're interested in getting rid of all of the stack allocated arrays in the
> kernel [1]. This patch simply hardcodes the iv length to match that of the
> hardcoded cipher.
>
> [1]: https://lkml.org/lkml/2018/3/7/621
>
> v2: hardcode the length of the nonce to be the GCM AES IV length, and do a
> sanity check in init(), Eric Biggers
>
> Signed-off-by: Tycho Andersen <[email protected]>
> CC: David Howells <[email protected]>
> CC: James Morris <[email protected]>
> CC: "Serge E. Hallyn" <[email protected]>
> CC: Jason A. Donenfeld <[email protected]>
> CC: Eric Biggers <[email protected]>
> ---
> security/keys/big_key.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/security/keys/big_key.c b/security/keys/big_key.c
> index 933623784ccd..75c46786a166 100644
> --- a/security/keys/big_key.c
> +++ b/security/keys/big_key.c
> @@ -22,6 +22,7 @@
> #include <keys/user-type.h>
> #include <keys/big_key-type.h>
> #include <crypto/aead.h>
> +#include <crypto/gcm.h>
>
> struct big_key_buf {
> unsigned int nr_pages;
> @@ -109,7 +110,7 @@ static int big_key_crypt(enum big_key_op op, struct
> big_key_buf *buf, size_t dat
> * an .update function, so there's no chance we'll wind up reusing the
> * key to encrypt updated data. Simply put: one key, one encryption.
> */
> - u8 zero_nonce[crypto_aead_ivsize(big_key_aead)];
> + u8 zero_nonce[GCM_AES_IV_SIZE];
>
> aead_req = aead_request_alloc(big_key_aead, GFP_KERNEL);
> if (!aead_req)
> @@ -425,6 +426,12 @@ static int __init big_key_init(void)
> pr_err("Can't alloc crypto: %d\n", ret);
> return ret;
> }
> +
> + if (unlikely(crypto_aead_ivsize(big_key_aead) != GCM_AES_IV_SIZE)) {
> + WARN(1, "big key algorithm changed?");
> + return -EINVAL;
> + }
> +
'big_key_aead' needs to be freed on error.
err = -EINVAL;
goto free_aead;
Also how about defining the IV size next to the algorithm name?
Then all the algorithm details would be on adjacent lines:
static const char big_key_alg_name[] = "gcm(aes)";
#define BIG_KEY_IV_SIZE GCM_AES_IV_SIZE
- Eric
