crypto: morus640 - Fix out-of-bounds access

We must load the block from the temporary variable here, not directly
from the input.

Also add forgotten zeroing-out of the uninitialized part of the
temporary block (as is done correctly in morus1280.c).

Fixes: 396be41f ("crypto: morus - Add generic MORUS AEAD implementations")
Reported-by: syzbot+1fafa9c4cf42df33f716@syzkaller.appspotmail.com
Reported-by: syzbot+d82643ba80bf6937cd44@syzkaller.appspotmail.com
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/morus640.c

@@ -274,8 +274,9 @@ static void crypto_morus640_decrypt_chunk(struct morus640_state *state, u8 *dst,
 		union morus640_block_in tail;
 
 		memcpy(tail.bytes, src, size);
+		memset(tail.bytes + size, 0, MORUS640_BLOCK_SIZE - size);
 
-		crypto_morus640_load_a(&m, src);
+		crypto_morus640_load_a(&m, tail.bytes);
 		crypto_morus640_core(state, &m);
 		crypto_morus640_store_a(tail.bytes, &m);
 		memset(tail.bytes + size, 0, MORUS640_BLOCK_SIZE - size);