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)

Change-Id: I9e6df0b1b97a9fde1ca8407793bdc9f4008db1c1
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>
Git-Repo: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Git-Commit: b350bee5ea0f4db75d4c6191a2e95db16f40c278
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>