[PATCH 5/6] crypto: cts - avoid VLA use

From: Salvatore Mesoraca
Date: Mon Apr 09 2018 - 09:54:31 EST


We avoid 2 VLAs[1] by always allocating MAX_BLOCKSIZE*2 bytes.
We also check the selected cipher at instance creation time, if
it doesn't comply with these limits, the creation will fail.

[1] http://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@xxxxxxxxxxxxxx

Signed-off-by: Salvatore Mesoraca <s.mesoraca16@xxxxxxxxx>
---
crypto/cts.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/crypto/cts.c b/crypto/cts.c
index 4773c18..12e6bd3 100644
--- a/crypto/cts.c
+++ b/crypto/cts.c
@@ -50,6 +50,7 @@
#include <crypto/scatterwalk.h>
#include <linux/slab.h>
#include <linux/compiler.h>
+#include "internal.h"

struct crypto_cts_ctx {
struct crypto_skcipher *child;
@@ -104,7 +105,7 @@ static int cts_cbc_encrypt(struct skcipher_request *req)
struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
struct skcipher_request *subreq = &rctx->subreq;
int bsize = crypto_skcipher_blocksize(tfm);
- u8 d[bsize * 2] __aligned(__alignof__(u32));
+ u8 d[MAX_BLOCKSIZE * 2] __aligned(__alignof__(u32));
struct scatterlist *sg;
unsigned int offset;
int lastn;
@@ -183,7 +184,7 @@ static int cts_cbc_decrypt(struct skcipher_request *req)
struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
struct skcipher_request *subreq = &rctx->subreq;
int bsize = crypto_skcipher_blocksize(tfm);
- u8 d[bsize * 2] __aligned(__alignof__(u32));
+ u8 d[MAX_BLOCKSIZE * 2] __aligned(__alignof__(u32));
struct scatterlist *sg;
unsigned int offset;
u8 *space;
@@ -359,6 +360,9 @@ static int crypto_cts_create(struct crypto_template *tmpl, struct rtattr **tb)
if (crypto_skcipher_alg_ivsize(alg) != alg->base.cra_blocksize)
goto err_drop_spawn;

+ if (alg->base.cra_blocksize > MAX_BLOCKSIZE)
+ goto err_drop_spawn;
+
if (strncmp(alg->base.cra_name, "cbc(", 4))
goto err_drop_spawn;

--
1.9.1