crypto: xcbc - Remove VLA usage

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

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/crypto/xcbc.c b/crypto/xcbc.c
index 25c75af..c055f57 100644 (file)
--- a/crypto/xcbc.c
+++ b/crypto/xcbc.c
@@ -57,15 +57,17 @@ 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)
 {
        unsigned long alignmask = crypto_shash_alignmask(parent);
        struct xcbc_tfm_ctx *ctx = crypto_shash_ctx(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];
+       int bs = sizeof(key1);
 
        if ((err = crypto_cipher_setkey(ctx->child, inkey, keylen)))
                return err;
@@ -212,7 +214,7 @@ 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;