libceph: Remove VLA usage of skcipher

In the quest to remove all stack VLA usage from the kernel[1], this
replaces struct crypto_skcipher and SKCIPHER_REQUEST_ON_STACK() usage
with struct crypto_sync_skcipher and SYNC_SKCIPHER_REQUEST_ON_STACK(),
which uses a fixed stack size.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=[e-mail]

Cc: Ilya Dryomov <[e-mail]>
Cc: "Yan, Zheng" <[e-mail]>
Cc: Sage Weil <[e-mail]>
Cc: [e-mail]
Signed-off-by: Kees Cook <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

net/ceph/crypto.c

···
 		goto fail;
 	}
 
-	/* crypto_alloc_skcipher() allocates with GFP_KERNEL */
+	/* crypto_alloc_sync_skcipher() allocates with GFP_KERNEL */
 	noio_flag = memalloc_noio_save();
-	key->tfm = crypto_alloc_skcipher("cbc(aes)", 0, CRYPTO_ALG_ASYNC);
+	key->tfm = crypto_alloc_sync_skcipher("cbc(aes)", 0, 0);
 	memalloc_noio_restore(noio_flag);
 	if (IS_ERR(key->tfm)) {
 		ret = PTR_ERR(key->tfm);
···
 		goto fail;
 	}
 
-	ret = crypto_skcipher_setkey(key->tfm, key->key, key->len);
+	ret = crypto_sync_skcipher_setkey(key->tfm, key->key, key->len);
 	if (ret)
 		goto fail;
 
···
 	if (key) {
 		kfree(key->key);
 		key->key = NULL;
-		crypto_free_skcipher(key->tfm);
+		crypto_free_sync_skcipher(key->tfm);
 		key->tfm = NULL;
 	}
 }
···
 static int ceph_aes_crypt(const struct ceph_crypto_key *key, bool encrypt,
 			  void *buf, int buf_len, int in_len, int *pout_len)
 {
-	SKCIPHER_REQUEST_ON_STACK(req, key->tfm);
+	SYNC_SKCIPHER_REQUEST_ON_STACK(req, key->tfm);
 	struct sg_table sgt;
 	struct scatterlist prealloc_sg;
 	char iv[AES_BLOCK_SIZE] __aligned(8);
···
 		return ret;
 
 	memcpy(iv, aes_iv, AES_BLOCK_SIZE);
-	skcipher_request_set_tfm(req, key->tfm);
+	skcipher_request_set_sync_tfm(req, key->tfm);
 	skcipher_request_set_callback(req, 0, NULL, NULL);
 	skcipher_request_set_crypt(req, sgt.sgl, sgt.sgl, crypt_len, iv);
 

net/ceph/crypto.h

···
 	struct ceph_timespec created;
 	int len;
 	void *key;
-	struct crypto_skcipher *tfm;
+	struct crypto_sync_skcipher *tfm;
 };
 
 int ceph_crypto_key_clone(struct ceph_crypto_key *dst,