Merge bitcoin/bitcoin#30444: rest: Reject negative outpoint index early in getutxos parsing

fac932bf93d9bd8cb7bef93f04ecf48ea2ccf1d1 refactor: Use util::Split to avoid a harmless unsigned-integer-overflow (MarcoFalke)
fab54db9f1d0e634f4a697480dbb87b87940dc5c rest: Reject negative outpoint index in getutxos parsing (MarcoFalke)

Pull request description:

  In `rest_getutxos` outpoint indexes such as `+N` or `-N` are accepted. This should be harmless, because any index out of range should be treated as a non-existent utxo. However, a negative index can't exist ever, so it seems better to reject all signs, whether `+` or `-`.

ACKs for top commit:
  achow101:
    ACK fac932bf93d9bd8cb7bef93f04ecf48ea2ccf1d1
  hodlinator:
    ut-ACK fac932bf93d9bd8cb7bef93f04ecf48ea2ccf1d1
  tdb3:
    re ACK fac932bf93d9bd8cb7bef93f04ecf48ea2ccf1d1
  danielabrozzoni:
    ACK fac932bf93d9bd8cb7bef93f04ecf48ea2ccf1d1
  brunoerg:
    reACK fac932bf93d9bd8cb7bef93f04ecf48ea2ccf1d1

Tree-SHA512: 8f1a75248cb61e1c4beceded6ed170db83b07f30fbcf93a26acfffc00ec4546572366eff87907a7e1423d7d3a2a9e57a0a7a9bacb787c86463f842d7161c16bc

2 files changed, 12 insertions, 6 deletions

diff --git a/src/rest.cpp b/src/rest.cpp
index 4abbc4d2ca..3cf6ad343c 100644
--- a/src/rest.cpp
+++ b/src/rest.cpp
@@ -788,14 +788,17 @@ static bool rest_getutxos(const std::any& context, HTTPRequest* req, const std::
 
         for (size_t i = (fCheckMemPool) ? 1 : 0; i < uriParts.size(); i++)
         {
-            int32_t nOutput;
-            std::string strTxid = uriParts[i].substr(0, uriParts[i].find('-'));
-            std::string strOutput = uriParts[i].substr(uriParts[i].find('-')+1);
+            const auto txid_out{util::Split<std::string_view>(uriParts[i], '-')};
+            if (txid_out.size() != 2) {
+                return RESTERR(req, HTTP_BAD_REQUEST, "Parse error");
+            }
+            auto output{ToIntegral<uint32_t>(txid_out.at(1))};
 
-            if (!ParseInt32(strOutput, &nOutput) || !IsHex(strTxid))
+            if (!output || !IsHex(txid_out.at(0))) {
                 return RESTERR(req, HTTP_BAD_REQUEST, "Parse error");
+            }
 
-            vOutPoints.emplace_back(TxidFromString(strTxid), (uint32_t)nOutput);
+            vOutPoints.emplace_back(TxidFromString(txid_out.at(0)), *output);
         }
 
         if (vOutPoints.size() > 0)
diff --git a/test/functional/interface_rest.py b/test/functional/interface_rest.py
index ae8d6b226d..aa201cb85b 100755
--- a/test/functional/interface_rest.py
+++ b/test/functional/interface_rest.py
@@ -201,10 +201,13 @@ class RESTTest (BitcoinTestFramework):
         json_obj = self.test_rest_request(f"/getutxos/checkmempool/{spending[0]}-{spending[1]}")
         assert_equal(len(json_obj['utxos']), 1)
 
-        # Do some invalid requests
+        self.log.info("Check some invalid requests")
         self.test_rest_request("/getutxos", http_method='POST', req_type=ReqType.JSON, body='{"checkmempool', status=400, ret_type=RetType.OBJ)
         self.test_rest_request("/getutxos", http_method='POST', req_type=ReqType.BIN, body='{"checkmempool', status=400, ret_type=RetType.OBJ)
         self.test_rest_request("/getutxos/checkmempool", http_method='POST', req_type=ReqType.JSON, status=400, ret_type=RetType.OBJ)
+        self.test_rest_request(f"/getutxos/{spending[0]}_+1", ret_type=RetType.OBJ, status=400)
+        self.test_rest_request(f"/getutxos/{spending[0]}-+1", ret_type=RetType.OBJ, status=400)
+        self.test_rest_request(f"/getutxos/{spending[0]}--1", ret_type=RetType.OBJ, status=400)
 
         # Test limits
         long_uri = '/'.join([f"{txid}-{n_}" for n_ in range(20)])