From 209a1a6ffa5c60128b1a759f090facdfa08e6b91 Mon Sep 17 00:00:00 2001
From: Olek <115580134+oleks-rip@users.noreply.github.com>
Date: Thu, 15 Jan 2026 19:52:22 -0500
Subject: [PATCH] Don't throw from hostfunctions stack (#6221)

---
 src/xrpld/app/wasm/WasmiVM.h                  |  1 +
 src/xrpld/app/wasm/detail/HostFuncWrapper.cpp |  9 +++++-
 src/xrpld/app/wasm/detail/WasmiVM.cpp         | 30 ++++++++++++++-----
 3 files changed, 31 insertions(+), 9 deletions(-)

diff --git a/src/xrpld/app/wasm/WasmiVM.h b/src/xrpld/app/wasm/WasmiVM.h
index c39b577c46..0d051ea49b 100644
--- a/src/xrpld/app/wasm/WasmiVM.h
+++ b/src/xrpld/app/wasm/WasmiVM.h
@@ -108,6 +108,7 @@ struct InstanceWrapper
 {
     wasm_store_t* store_ = nullptr;
     WasmExternVec exports_;
+    mutable int memIdx_ = -1;
     InstancePtr instance_;
     beast::Journal j_ = beast::Journal(beast::Journal::getNullSink());
 
diff --git a/src/xrpld/app/wasm/detail/HostFuncWrapper.cpp b/src/xrpld/app/wasm/detail/HostFuncWrapper.cpp
index ee284fa6e9..8910f22aa1 100644
--- a/src/xrpld/app/wasm/detail/HostFuncWrapper.cpp
+++ b/src/xrpld/app/wasm/detail/HostFuncWrapper.cpp
@@ -332,7 +332,14 @@ checkGas(void* env)
     int64_t const gas = runtime->getGas();
     WasmImportFunc const& impFunc = udata->second;
     int64_t const x = gas >= impFunc.gas ? gas - impFunc.gas : 0;
-    runtime->setGas(x);
+
+    if (runtime->setGas(x) < 0)
+    {
+        wasm_trap_t* trap = reinterpret_cast<wasm_trap_t*>(
+            WasmEngine::instance().newTrap("can't set gas"));  // LCOV_EXCL_LINE
+        return Unexpected(trap);                               // LCOV_EXCL_LINE
+    }
+
     if (gas < impFunc.gas)
     {
         wasm_trap_t* trap = reinterpret_cast<wasm_trap_t*>(
diff --git a/src/xrpld/app/wasm/detail/WasmiVM.cpp b/src/xrpld/app/wasm/detail/WasmiVM.cpp
index 3c56f885dd..8bd4a7b8b8 100644
--- a/src/xrpld/app/wasm/detail/WasmiVM.cpp
+++ b/src/xrpld/app/wasm/detail/WasmiVM.cpp
@@ -103,6 +103,8 @@ InstanceWrapper::operator=(InstanceWrapper&& o)
     store_ = o.store_;
     o.store_ = nullptr;
     exports_ = std::move(o.exports_);
+    memIdx_ = o.memIdx_;
+    o.memIdx_ = -1;
     instance_ = std::move(o.instance_);
 
     j_ = o.j_;
@@ -162,22 +164,29 @@ InstanceWrapper::getFunc(
 wmem
 InstanceWrapper::getMem() const
 {
-    if (!instance_)
-        throw std::runtime_error("no instance");  // LCOV_EXCL_LINE
+    if (memIdx_ >= 0)
+    {
+        auto* e(exports_.vec_.data[memIdx_]);
+        wasm_memory_t* mem = wasm_extern_as_memory(e);
+        return {
+            reinterpret_cast<std::uint8_t*>(wasm_memory_data(mem)),
+            wasm_memory_data_size(mem)};
+    }
 
     wasm_memory_t* mem = nullptr;
-    for (unsigned i = 0; i < exports_.vec_.size; ++i)
+    for (int i = 0; i < exports_.vec_.size; ++i)
     {
         auto* e(exports_.vec_.data[i]);
         if (wasm_extern_kind(e) == WASM_EXTERN_MEMORY)
         {
+            memIdx_ = i;
             mem = wasm_extern_as_memory(e);
             break;
         }
     }
 
     if (!mem)
-        throw std::runtime_error("no memory exported");  // LCOV_EXCL_LINE
+        return {};  // LCOV_EXCL_LINE
 
     return {
         reinterpret_cast<std::uint8_t*>(wasm_memory_data(mem)),
@@ -209,7 +218,7 @@ InstanceWrapper::setGas(std::int64_t gas) const
         // LCOV_EXCL_START
         print_wasm_error("Can't set instance gas", nullptr, j_);
         wasmi_error_delete(err);
-        throw std::runtime_error("Can't set instance gas");
+        return -1;
         // LCOV_EXCL_STOP
     }
 
@@ -592,11 +601,13 @@ WasmiEngine::convertParams(std::vector<WasmParam> const& params)
                 break;
             // LCOV_EXCL_STOP
             case WT_U8V: {
+                auto mem = getMem();
+                if (!mem.s)
+                    throw std::runtime_error(
+                        "no memory exported");  // LCOV_EXCL_LINE
                 auto const sz = p.of.u8v.sz;
                 auto const ptr = allocate(sz);
-                auto mem = getMem();
                 memcpy(mem.p + ptr, p.of.u8v.d, sz);
-
                 v.push_back(WASM_I32_VAL(ptr));
                 v.push_back(WASM_I32_VAL(sz));
             }
@@ -751,8 +762,11 @@ WasmiEngine::call(
     std::size_t sz,
     Types&&... args)
 {
-    auto const ptr = allocate(sz);
     auto mem = getMem();
+    if (!mem.s)
+        throw std::runtime_error("no memory exported");  // LCOV_EXCL_LINE
+
+    auto const ptr = allocate(sz);
     memcpy(mem.p + ptr, d, sz);
 
     add_param(in, ptr);