siphash: Properly set mac size in sipcopy

Also fully duplicate the context on dup

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/18142)

providers/implementations/macs/siphash_prov.c

diff --git a/providers/implementations/macs/siphash_prov.c b/providers/implementations/macs/siphash_prov.c
index 2a291d7..35265e5 100644
--- a/providers/implementations/macs/siphash_prov.c
+++ b/providers/implementations/macs/siphash_prov.c
@@ -77,11 +77,11 @@
 
     if (!ossl_prov_is_running())
         return NULL;
-    sdst = siphash_new(ssrc->provctx);
+    sdst = OPENSSL_malloc(sizeof(*sdst));
     if (sdst == NULL)
         return NULL;
 
-    sdst->siphash = ssrc->siphash;
+    *sdst = *ssrc;
     return sdst;
 }
 
@@ -112,7 +112,8 @@
 
     if (!ossl_prov_is_running() || !siphash_set_params(ctx, params))
         return 0;
-    /* Without a key, there is not much to do here,
+    /*
+     * Without a key, there is not much to do here,
      * The actual initialization happens through controls.
      */
     if (key == NULL) {
@@ -202,7 +203,8 @@
 
     if ((p = OSSL_PARAM_locate_const(params, OSSL_MAC_PARAM_SIZE)) != NULL) {
         if (!OSSL_PARAM_get_size_t(p, &size)
-            || !SipHash_set_hash_size(&ctx->siphash, size))
+            || !SipHash_set_hash_size(&ctx->siphash, size)
+            || !SipHash_set_hash_size(&ctx->sipcopy, size))
             return 0;
     }
     if ((p = OSSL_PARAM_locate_const(params, OSSL_MAC_PARAM_C_ROUNDS)) != NULL