fix: support rootless ICMP and verify SELinux deployment [CI]

backend/shared/tests/MoShiro.Measurement.Tests/IcmpReplyTests.cs

@@ -0,0 +1,31 @@
+using System.Buffers.Binary;
+
+namespace MoShiro.Measurement.Tests;
+
+public sealed class IcmpReplyTests
+{
+    [Theory]
+    [InlineData((byte)0)]
+    [InlineData((byte)129)]
+    public void ReplyMustMatchTypeCodeSequenceAndPayload(byte replyType)
+    {
+        byte[] request = new byte[44];
+        request[8] = 71;
+        byte[] reply = (byte[])request.Clone();
+        reply[0] = replyType;
+        BinaryPrimitives.WriteUInt16BigEndian(reply.AsSpan(6), 123);
+        // Linux changes the identifier; it is not the request's zero identifier.
+        reply[4] = 42;
+        Assert.True(LinuxIcmpEcho.IsReply(reply, request, replyType, 123));
+        Assert.False(LinuxIcmpEcho.IsReply(reply, request, replyType, 124));
+        Assert.False(LinuxIcmpEcho.IsReply(reply.AsSpan(0, 7), request, replyType, 123));
+        reply[1] = 1;
+        Assert.False(LinuxIcmpEcho.IsReply(reply, request, replyType, 123));
+        reply[1] = 0;
+        reply[0]++;
+        Assert.False(LinuxIcmpEcho.IsReply(reply, request, replyType, 123));
+        reply[0] = replyType;
+        reply[8]++;
+        Assert.False(LinuxIcmpEcho.IsReply(reply, request, replyType, 123));
+    }
+}