bugfix: rest: avoid segfault for invalid URI

`evhttp_uri_parse` can return a nullptr, for example when the URI
contains invalid characters (e.g. "%").
`GetQueryParameterFromUri` passes the output of `evhttp_uri_parse`
straight into `evhttp_uri_get_query`, which means that anyone calling
a REST endpoint in which query parameters are used (e.g. `rest_headers`)
can cause a segfault.

This bugfix is designed to be minimal and without additional behaviour change.
Follow-up work should be done to resolve this in a more general and robust way,
so not every endpoint has to handle it individually.

1 files changed, 22 insertions, 4 deletions

diff --git a/src/rest.cpp b/src/rest.cpp
index fa119ddfb7..e46406f1ad 100644
--- a/src/rest.cpp
+++ b/src/rest.cpp
@@ -200,7 +200,11 @@ static bool rest_headers(const std::any& context,
     } else if (path.size() == 1) {
         // new path with query parameter: /rest/headers/<hash>?count=<count>
         hashStr = path[0];
-        raw_count = req->GetQueryParameter("count").value_or("5");
+        try {
+            raw_count = req->GetQueryParameter("count").value_or("5");
+        } catch (const std::runtime_error& e) {
+            return RESTERR(req, HTTP_BAD_REQUEST, e.what());
+        }
     } else {
         return RESTERR(req, HTTP_BAD_REQUEST, "Invalid URI format. Expected /rest/headers/<hash>.<ext>?count=<count>");
     }
@@ -371,7 +375,11 @@ static bool rest_filter_header(const std::any& context, HTTPRequest* req, const
     } else if (uri_parts.size() == 2) {
         // new path with query parameter: /rest/blockfilterheaders/<filtertype>/<blockhash>?count=<count>
         raw_blockhash = uri_parts[1];
-        raw_count = req->GetQueryParameter("count").value_or("5");
+        try {
+            raw_count = req->GetQueryParameter("count").value_or("5");
+        } catch (const std::runtime_error& e) {
+            return RESTERR(req, HTTP_BAD_REQUEST, e.what());
+        }
     } else {
         return RESTERR(req, HTTP_BAD_REQUEST, "Invalid URI format. Expected /rest/blockfilterheaders/<filtertype>/<blockhash>.<ext>?count=<count>");
     }
@@ -652,11 +660,21 @@ static bool rest_mempool(const std::any& context, HTTPRequest* req, const std::s
     case RESTResponseFormat::JSON: {
         std::string str_json;
         if (param == "contents") {
-            const std::string raw_verbose{req->GetQueryParameter("verbose").value_or("true")};
+            std::string raw_verbose;
+            try {
+                raw_verbose = req->GetQueryParameter("verbose").value_or("true");
+            } catch (const std::runtime_error& e) {
+                return RESTERR(req, HTTP_BAD_REQUEST, e.what());
+            }
             if (raw_verbose != "true" && raw_verbose != "false") {
                 return RESTERR(req, HTTP_BAD_REQUEST, "The \"verbose\" query parameter must be either \"true\" or \"false\".");
             }
-            const std::string raw_mempool_sequence{req->GetQueryParameter("mempool_sequence").value_or("false")};
+            std::string raw_mempool_sequence;
+            try {
+                raw_mempool_sequence = req->GetQueryParameter("mempool_sequence").value_or("false");
+            } catch (const std::runtime_error& e) {
+                return RESTERR(req, HTTP_BAD_REQUEST, e.what());
+            }
             if (raw_mempool_sequence != "true" && raw_mempool_sequence != "false") {
                 return RESTERR(req, HTTP_BAD_REQUEST, "The \"mempool_sequence\" query parameter must be either \"true\" or \"false\".");
             }