[PATCH v2 01/11] crypto: xcbc: Remove VLA usage

Kees Cook
2018-06-25T21:10:47Z

In the quest to remove all stack VLA usage from the kernel[1], this uses
the maximum blocksize and adds a sanity check. For xcbc, the blocksize
must always be 16, so use that, since it's already being enforced during
instantiation.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: linux-crypto@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
crypto/xcbc.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/crypto/xcbc.c b/crypto/xcbc.c
index 25c75af50d3f..7aa03beed795 100644
--- a/crypto/xcbc.c
+++ b/crypto/xcbc.c
@@ -57,6 +57,8 @@ struct xcbc_desc_ctx {
u8 ctx[];
};

+#define XCBC_BLOCKSIZE 16
+
static int crypto_xcbc_digest_setkey(struct crypto_shash *parent,
const u8 *inkey, unsigned int keylen)
{
@@ -65,7 +67,10 @@ static int crypto_xcbc_digest_setkey(struct crypto_shash *parent,
int bs = crypto_shash_blocksize(parent);
u8 *consts = PTR_ALIGN(&ctx->ctx[0], alignmask + 1);
int err = 0;
- u8 key1[bs];
+ u8 key1[XCBC_BLOCKSIZE];
+
+ if (WARN_ON(bs > sizeof(key1)))
+ return -EINVAL;

if ((err = crypto_cipher_setkey(ctx->child, inkey, keylen)))
return err;
@@ -212,7 +217,7 @@ static int xcbc_create(struct crypto_template *tmpl, struct rtattr **tb)
return PTR_ERR(alg);

switch(alg->cra_blocksize) {
- case 16:
+ case XCBC_BLOCKSIZE:
break;
default:
goto out_put_alg;
--
2.17.1