Auto-generated `.csproj` for C# submissions includes `<AllowUnsafeBlocks>true</AllowUnsafeBlocks>`

[FedorPortnoi]

Summary

When compiling a .cs_net7 submission, the ECS runner auto-generates a project file that includes <AllowUnsafeBlocks>true</AllowUnsafeBlocks>. This enables unsafe code in all submitted C# solutions without restriction.

Affected File

ecs-runner/src/main/java/com/topcoder/runner/EcsRunnerMain.java, lines 3288–3301

Files.write(csproj, Arrays.asList(
    "<Project Sdk=\"Microsoft.NET.Sdk\">",
    "  <PropertyGroup>",
    "    <TargetFramework>net7.0</TargetFramework>",
    "    <OutputType>Exe</OutputType>",
    "    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>",   // ← here
    "  </PropertyGroup>",
    "</Project>"
), StandardCharsets.UTF_8);

Impact

With unsafe enabled, a C# submission can:

1. Use raw pointer arithmetic — allows reading/writing arbitrary memory addresses within the process
2. Call native code via P/Invoke — combined with unsafe blocks, the submission can invoke open, read, mmap, and other native syscalls that are not blocked by the seccomp filter (which only blocks socket() and socketpair())
3. Enumerate /proc filesystem via native opendir/readdir calls without triggering any seccomp rule
4. Read other files in the container (/tmp/mm-isolated-scorer-*.json, /tmp/tester-*.jar, etc.) using native file I/O even if managed I/O were somehow restricted

The seccomp filter in mm-net-isolate.c only blocks network socket creation. Enabling unsafe C# code opens a direct path to all other OS-level operations.

Expected

Remove <AllowUnsafeBlocks>true</AllowUnsafeBlocks> from the generated project file. Competitive programming problems do not require unsafe memory access. If a specific challenge needs it, it should be an explicit opt-in configured per-challenge rather than a global default.

Severity: Medium

[eulerscheZahl]

AllowUnsafeBlocks is a feature and documented!
User submissions are executed in a sandbox for a reason. And unsafe doesn't open any security risks that you don't already have by allowing C++ submissions.