bcachefs: use library APIs for ChaCha20 and Poly1305

Just use the ChaCha20 and Poly1305 libraries instead of the clunky
crypto API.  This is much simpler.  It is also slightly faster, since
the libraries provide more direct access to the same
architecture-optimized ChaCha20 and Poly1305 code.

I've tested that existing encrypted bcachefs filesystems can be continue
to be accessed with this patch applied.

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Author: ebiggers

fs/bcachefs/Kconfig

@@ -15,10 +15,9 @@ config BCACHEFS_FS
 	select ZLIB_INFLATE
 	select ZSTD_COMPRESS
 	select ZSTD_DECOMPRESS
-	select CRYPTO
 	select CRYPTO_LIB_SHA256
-	select CRYPTO_CHACHA20
-	select CRYPTO_POLY1305
+	select CRYPTO_LIB_CHACHA
+	select CRYPTO_LIB_POLY1305
 	select KEYS
 	select RAID6_PQ
 	select XOR_BLOCKS

fs/bcachefs/bcachefs.h

@@ -981,8 +981,8 @@ struct bch_fs {
 	mempool_t		compress_workspace[BCH_COMPRESSION_OPT_NR];
 	size_t			zstd_workspace_size;
 
-	struct crypto_sync_skcipher *chacha20;
-	struct crypto_shash	*poly1305;
+	struct bch_key		chacha20_key;
+	bool			chacha20_key_set;
 
 	atomic64_t		key_version;
 

fs/bcachefs/btree_node_scan.c

@@ -183,7 +183,7 @@ static void try_read_btree_node(struct find_btree_nodes *f, struct bch_dev *ca,
 		return;
 
 	if (bch2_csum_type_is_encryption(BSET_CSUM_TYPE(&bn->keys))) {
-		if (!c->chacha20)
+		if (!c->chacha20_key_set)
 			return;
 
 		struct nonce nonce = btree_nonce(&bn->keys, 0);