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Date: Mon, 23 Apr 2018 21:50:15 -0700
From: Eric Biggers <ebiggers3@...il.com>
To: Tycho Andersen <tycho@...ho.ws>
Cc: David Howells <dhowells@...hat.com>, keyrings@...r.kernel.org,
linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel-hardening@...ts.openwall.com,
James Morris <jmorris@...ei.org>,
"Serge E. Hallyn" <serge@...lyn.com>,
"Jason A . Donenfeld" <Jason@...c4.com>
Subject: Re: [PATCH 1/3] big key: get rid of stack array allocation
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 <tycho@...ho.ws>
> CC: David Howells <dhowells@...hat.com>
> CC: James Morris <jmorris@...ei.org>
> CC: "Serge E. Hallyn" <serge@...lyn.com>
> CC: Jason A. Donenfeld <Jason@...c4.com>
> CC: Eric Biggers <ebiggers3@...il.com>
> ---
> 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
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