Remove lh_new's default hash and comparator.

This is a memory error for anything other than LHASH_OF(char), which
does not exist.

No code outside the library creates (or even queries) an LHASH, so we
can change this module freely.

Change-Id: Ifbc7a1c69a859e07650fcfaa067bdfc68d83fbbc
Reviewed-on: https://boringssl-review.googlesource.com/12978
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>

crypto/lhash/lhash.c

@@ -74,9 +74,7 @@ static const size_t kMaxAverageChainLength = 2;
 static const size_t kMinAverageChainLength = 1;
 
 _LHASH *lh_new(lhash_hash_func hash, lhash_cmp_func comp) {
-  _LHASH *ret;
-
-  ret = OPENSSL_malloc(sizeof(_LHASH));
+  _LHASH *ret = OPENSSL_malloc(sizeof(_LHASH));
   if (ret == NULL) {
     return NULL;
   }
@@ -91,14 +89,7 @@ _LHASH *lh_new(lhash_hash_func hash, lhash_cmp_func comp) {
   OPENSSL_memset(ret->buckets, 0, sizeof(LHASH_ITEM *) * ret->num_buckets);
 
   ret->comp = comp;
-  if (ret->comp == NULL) {
-    ret->comp = (lhash_cmp_func) strcmp;
-  }
   ret->hash = hash;
-  if (ret->hash == NULL) {
-    ret->hash = (lhash_hash_func) lh_strhash;
-  }
-
   return ret;
 }
 

crypto/lhash/lhash_test.cc

@@ -60,7 +60,8 @@ static const char *Lookup(
 int main(int argc, char **argv) {
   CRYPTO_library_init();
 
-  std::unique_ptr<_LHASH, FreeLHASH> lh(lh_new(NULL, NULL));
+  std::unique_ptr<_LHASH, FreeLHASH> lh(
+      lh_new((lhash_hash_func)lh_strhash, (lhash_cmp_func)strcmp));
   if (!lh) {
     return 1;
   }

include/openssl/lhash.h

@@ -144,9 +144,7 @@ typedef struct lhash_st {
   lhash_hash_func hash;
 } _LHASH;
 
-/* lh_new returns a new, empty hash table or NULL on error. If |comp| is NULL,
- * |strcmp| will be used. If |hash| is NULL, a generic hash function will be
- * used. */
+/* lh_new returns a new, empty hash table or NULL on error. */
 OPENSSL_EXPORT _LHASH *lh_new(lhash_hash_func hash, lhash_cmp_func comp);
 
 /* lh_free frees the hash table itself but none of the elements. See