crypto: lib/chachapoly - Drop dependency on CRYPTO_ALGAPI

The ChaCha20-Poly1305 library code uses the sg_miter API to process
input presented via scatterlists, except for the special case where the
digest buffer is not covered entirely by the same scatterlist entry as
the last byte of input. In that case, it uses scatterwalk_map_and_copy()
to access the memory in the input scatterlist where the digest is stored.

This results in a dependency on crypto/scatterwalk.c and therefore on
CONFIG_CRYPTO_ALGAPI, which is unnecessary, as the sg_miter API already
provides this functionality via sg_copy_to_buffer(). So use that
instead, and drop the dependencies on CONFIG_CRYPTO_ALGAPI and
CONFIG_CRYPTO.

Reported-by: Arnd Bergmann <[e-mail]>
Acked-by: Eric Biggers <[e-mail]>
Signed-off-by: Ard Biesheuvel <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

lib/crypto/Kconfig

···
 
 config CRYPTO_LIB_CHACHA20POLY1305
 	tristate "ChaCha20-Poly1305 AEAD support (8-byte nonce library version)"
-	select CRYPTO
 	select CRYPTO_LIB_CHACHA
 	select CRYPTO_LIB_POLY1305
 	select CRYPTO_LIB_UTILS
-	select CRYPTO_ALGAPI
 
 config CRYPTO_LIB_SHA1
 	tristate

lib/crypto/chacha20poly1305.c

···
  * Information: https://tools.ietf.org/html/rfc8439
  */
 
-#include <crypto/algapi.h>
 #include <crypto/chacha20poly1305.h>
 #include <crypto/chacha.h>
 #include <crypto/poly1305.h>
-#include <crypto/scatterwalk.h>
+#include <crypto/utils.h>
 
 #include <linux/unaligned.h>
 #include <linux/kernel.h>
···
 
 	if (unlikely(sl > -POLY1305_DIGEST_SIZE)) {
 		poly1305_final(&poly1305_state, b.mac[1]);
-		scatterwalk_map_and_copy(b.mac[encrypt], src, src_len,
-					 sizeof(b.mac[1]), encrypt);
+		sg_copy_buffer(src, sg_nents(src), b.mac[encrypt],
+			       sizeof(b.mac[1]), src_len, !encrypt);
 		ret = encrypt ||
 		      !crypto_memneq(b.mac[0], b.mac[1], POLY1305_DIGEST_SIZE);
 	}