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Date: Tue, 8 May 2018 16:14:25 -0700
From: Kees Cook <keescook@...omium.org>
To: Tycho Andersen <tycho@...ho.ws>
Cc: David Howells <dhowells@...hat.com>, keyrings@...r.kernel.org,
linux-security-module <linux-security-module@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>, James Morris <jmorris@...ei.org>,
"Serge E. Hallyn" <serge@...lyn.com>, "Jason A . Donenfeld" <Jason@...c4.com>, Eric Biggers <ebiggers3@...il.com>
Subject: Re: [PATCH v3 1/3] big key: get rid of stack array allocation
On Tue, Apr 24, 2018 at 1:26 PM, Tycho Andersen <tycho@...ho.ws> 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
> v3: * remember to free big_key_aead when sanity check fails
> * define a constant for big key IV size so it can be changed along side
> the algorithm in the code
>
> 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>
Please consider this and patches 2 and 3:
Reviewed-by: Kees Cook <keescook@...omium.org>
James, are these something you can take into your tree?
Thanks!
-Kees
> ---
> security/keys/big_key.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/security/keys/big_key.c b/security/keys/big_key.c
> index 933623784ccd..2806e70d7f8f 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;
> @@ -85,6 +86,7 @@ struct key_type key_type_big_key = {
> * Crypto names for big_key data authenticated encryption
> */
> static const char big_key_alg_name[] = "gcm(aes)";
> +#define BIG_KEY_IV_SIZE GCM_AES_IV_SIZE
>
> /*
> * Crypto algorithms for big_key data authenticated encryption
> @@ -109,7 +111,7 @@ 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[BIG_KEY_IV_SIZE];
>
> aead_req = aead_request_alloc(big_key_aead, GFP_KERNEL);
> if (!aead_req)
> @@ -425,6 +427,13 @@ 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) != BIG_KEY_IV_SIZE)) {
> + WARN(1, "big key algorithm changed?");
> + ret = -EINVAL;
> + goto free_aead;
> + }
> +
> ret = crypto_aead_setauthsize(big_key_aead, ENC_AUTHTAG_SIZE);
> if (ret < 0) {
> pr_err("Can't set crypto auth tag len: %d\n", ret);
> --
> 2.17.0
>
--
Kees Cook
Pixel Security
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