crypto: skcipher - Introduce crypto_sync_skcipher

In preparation for removal of VLAs due to skcipher requests on the stack
via SKCIPHER_REQUEST_ON_STACK() usage, this introduces the infrastructure
for the "sync skcipher" tfm, which is for handling the on-stack cases of
skcipher, which are always non-ASYNC and have a known limited request
size.

The crypto API additions:

	struct crypto_sync_skcipher (wrapper for struct crypto_skcipher)
	crypto_alloc_sync_skcipher()
	crypto_free_sync_skcipher()
	crypto_sync_skcipher_setkey()
	crypto_sync_skcipher_get_flags()
	crypto_sync_skcipher_set_flags()
	crypto_sync_skcipher_clear_flags()
	crypto_sync_skcipher_blocksize()
	crypto_sync_skcipher_ivsize()
	crypto_sync_skcipher_reqtfm()
	skcipher_request_set_sync_tfm()
	SYNC_SKCIPHER_REQUEST_ON_STACK() (with tfm type check)

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 24 insertions, 0 deletions

diff --git a/crypto/skcipher.c b/crypto/skcipher.c
index 0bd8c6caa498..4caab81d2d02 100644
--- a/crypto/skcipher.c
+++ b/crypto/skcipher.c
@@ -949,6 +949,30 @@ struct crypto_skcipher *crypto_alloc_skcipher(const char *alg_name,
 }
 EXPORT_SYMBOL_GPL(crypto_alloc_skcipher);
 
+struct crypto_sync_skcipher *crypto_alloc_sync_skcipher(
+				const char *alg_name, u32 type, u32 mask)
+{
+	struct crypto_skcipher *tfm;
+
+	/* Only sync algorithms allowed. */
+	mask |= CRYPTO_ALG_ASYNC;
+
+	tfm = crypto_alloc_tfm(alg_name, &crypto_skcipher_type2, type, mask);
+
+	/*
+	 * Make sure we do not allocate something that might get used with
+	 * an on-stack request: check the request size.
+	 */
+	if (!IS_ERR(tfm) && WARN_ON(crypto_skcipher_reqsize(tfm) >
+				    MAX_SYNC_SKCIPHER_REQSIZE)) {
+		crypto_free_skcipher(tfm);
+		return ERR_PTR(-EINVAL);
+	}
+
+	return (struct crypto_sync_skcipher *)tfm;
+}
+EXPORT_SYMBOL_GPL(crypto_alloc_sync_skcipher);
+
 int crypto_has_skcipher2(const char *alg_name, u32 type, u32 mask)
 {
 	return crypto_type_has_alg(alg_name, &crypto_skcipher_type2,