ensure no NULL is passed to memcpy

NULL is valid when size is 0, but memcpy uses nonnull attributes,
so let's not poke the bear

contrib/epee/src/buffer.cpp

@@ -64,6 +64,7 @@ void buffer::append(const void *data, size_t sz)
       size_t reserve = (((size() + sz) * 3 / 2) + 4095) & ~4095;
       new_storage.reserve(reserve);
       new_storage.resize(size());
+      if (size() > 0)
         memcpy(new_storage.data(), storage.data() + offset, storage.size() - offset);
       offset = 0;
       std::swap(storage, new_storage);

contrib/epee/src/wipeable_string.cpp

@@ -62,12 +62,14 @@ wipeable_string::wipeable_string(wipeable_string &&other)
 wipeable_string::wipeable_string(const std::string &other)
 {
   grow(other.size());
+  if (size() > 0)
     memcpy(buffer.data(), other.c_str(), size());
 }
 
 wipeable_string::wipeable_string(std::string &&other)
 {
   grow(other.size());
+  if (size() > 0)
     memcpy(buffer.data(), other.c_str(), size());
   if (!other.empty())
   {
@@ -79,6 +81,7 @@ wipeable_string::wipeable_string(std::string &&other)
 wipeable_string::wipeable_string(const char *s)
 {
   grow(strlen(s));
+  if (size() > 0)
     memcpy(buffer.data(), s, size());
 }
 
@@ -112,15 +115,19 @@ void wipeable_string::grow(size_t sz, size_t reserved)
   }
   size_t old_sz = buffer.size();
   std::unique_ptr<char[]> tmp{new char[old_sz]};
-  memcpy(tmp.get(), buffer.data(), old_sz * sizeof(char));
   if (old_sz > 0)
+  {
+    memcpy(tmp.get(), buffer.data(), old_sz * sizeof(char));
     memwipe(buffer.data(), old_sz * sizeof(char));
+  }
   buffer.reserve(reserved);
   buffer.resize(sz);
-  memcpy(buffer.data(), tmp.get(), old_sz * sizeof(char));
   if (old_sz > 0)
+  {
+    memcpy(buffer.data(), tmp.get(), old_sz * sizeof(char));
     memwipe(tmp.get(), old_sz * sizeof(char));
   }
+}
 
 void wipeable_string::push_back(char c)
 {

src/blockchain_db/lmdb/db_lmdb.cpp

@@ -1077,11 +1077,11 @@ void BlockchainLMDB::add_tx_amount_output_indices(const uint64_t tx_id,
 
   int result = 0;
 
-  int num_outputs = amount_output_indices.size();
+  size_t num_outputs = amount_output_indices.size();
 
   MDB_val_set(k_tx_id, tx_id);
   MDB_val v;
-  v.mv_data = (void *)amount_output_indices.data();
+  v.mv_data = num_outputs ? (void *)amount_output_indices.data() : (void*)"";
   v.mv_size = sizeof(uint64_t) * num_outputs;
   // LOG_PRINT_L1("tx_outputs[tx_hash] size: " << v.mv_size);
 

src/crypto/keccak.c

@@ -116,6 +116,7 @@ void keccak(const uint8_t *in, size_t inlen, uint8_t *md, int mdlen)
       local_abort("Bad keccak use");
     }
 
+    if (inlen > 0)
       memcpy(temp, in, inlen);
     temp[inlen++] = 1;
     memset(temp + inlen, 0, rsiz - inlen);