From 655d725f0c16620e66ee046510e1d8d137abd9a5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bart=C5=82omiej=20Dach?= <dach.bartlomiej@gmail.com>
Date: Tue, 10 Feb 2026 05:34:43 +0100
Subject: [PATCH] Perform extra checks when loading rulesets (#36641)

---
 osu.Game.Tests/Database/RulesetStoreTests.cs | 71 ++++++++++++++++++++
 osu.Game/Rulesets/RealmRulesetStore.cs       |  6 ++
 2 files changed, 77 insertions(+)

diff --git a/osu.Game.Tests/Database/RulesetStoreTests.cs b/osu.Game.Tests/Database/RulesetStoreTests.cs
index 29aec73770..7ef2429491 100644
--- a/osu.Game.Tests/Database/RulesetStoreTests.cs
+++ b/osu.Game.Tests/Database/RulesetStoreTests.cs
@@ -7,6 +7,7 @@ using System.Linq;
 using NUnit.Framework;
 using osu.Game.Beatmaps;
 using osu.Game.Rulesets;
+using osu.Game.Rulesets.Catch;
 using osu.Game.Rulesets.Difficulty;
 using osu.Game.Rulesets.Mods;
 using osu.Game.Rulesets.Osu;
@@ -116,6 +117,69 @@ namespace osu.Game.Tests.Database
             });
         }
 
+        [Test]
+        public void TestFakedRulesetIdIsDetected()
+        {
+            RunTestWithRealm((realm, storage) =>
+            {
+                LoadTestRuleset.HasImplementations = true;
+                LoadTestRuleset.Version = Ruleset.CURRENT_RULESET_API_VERSION;
+
+                var ruleset = new LoadTestRuleset();
+                string rulesetShortName = ruleset.RulesetInfo.ShortName;
+
+                realm.Write(r => r.Add(new RulesetInfo(rulesetShortName, ruleset.RulesetInfo.Name, ruleset.RulesetInfo.InstantiationInfo, 0)
+                {
+                    Available = true,
+                }));
+
+                Assert.That(realm.Run(r => r.Find<RulesetInfo>(rulesetShortName)!.Available), Is.True);
+
+                // Availability is updated on construction of a RealmRulesetStore
+                using var _ = new RealmRulesetStore(realm, storage);
+
+                Assert.That(realm.Run(r => r.Find<RulesetInfo>(rulesetShortName)!.Available), Is.False);
+            });
+        }
+
+        [Test]
+        public void TestMultipleRulesetWithSameOnlineIdsAreDetected()
+        {
+            RunTestWithRealm((realm, storage) =>
+            {
+                LoadTestRuleset.HasImplementations = true;
+                LoadTestRuleset.Version = Ruleset.CURRENT_RULESET_API_VERSION;
+                LoadTestRuleset.OnlineID = 2;
+
+                var first = new LoadTestRuleset();
+                var second = new CatchRuleset();
+
+                realm.Write(r => r.Add(new RulesetInfo(first.ShortName, first.RulesetInfo.Name, first.RulesetInfo.InstantiationInfo, first.RulesetInfo.OnlineID)
+                {
+                    Available = true,
+                }));
+                realm.Write(r => r.Add(new RulesetInfo(second.ShortName, second.RulesetInfo.Name, second.RulesetInfo.InstantiationInfo, second.RulesetInfo.OnlineID)
+                {
+                    Available = true,
+                }));
+
+                Assert.That(realm.Run(r => r.Find<RulesetInfo>(first.ShortName)!.Available), Is.True);
+                Assert.That(realm.Run(r => r.Find<RulesetInfo>(second.ShortName)!.Available), Is.True);
+
+                // Availability is updated on construction of a RealmRulesetStore
+                using var _ = new RealmRulesetStore(realm, storage);
+
+                Assert.That(realm.Run(r => r.Find<RulesetInfo>(first.ShortName)!.Available), Is.False);
+                Assert.That(realm.Run(r => r.Find<RulesetInfo>(second.ShortName)!.Available), Is.False);
+
+                realm.Write(r => r.Remove(r.Find<RulesetInfo>(first.ShortName)!));
+
+                using var __ = new RealmRulesetStore(realm, storage);
+
+                Assert.That(realm.Run(r => r.Find<RulesetInfo>(second.ShortName)!.Available), Is.True);
+            });
+        }
+
         private class LoadTestRuleset : Ruleset
         {
             public override string RulesetAPIVersionSupported => Version;
@@ -124,6 +188,13 @@ namespace osu.Game.Tests.Database
 
             public static string Version { get; set; } = CURRENT_RULESET_API_VERSION;
 
+            public static int OnlineID { get; set; } = -1;
+
+            public LoadTestRuleset()
+            {
+                RulesetInfo.OnlineID = OnlineID;
+            }
+
             public override IEnumerable<Mod> GetModsFor(ModType type)
             {
                 if (!HasImplementations)
diff --git a/osu.Game/Rulesets/RealmRulesetStore.cs b/osu.Game/Rulesets/RealmRulesetStore.cs
index b93110426b..52ea5f7f4b 100644
--- a/osu.Game/Rulesets/RealmRulesetStore.cs
+++ b/osu.Game/Rulesets/RealmRulesetStore.cs
@@ -93,6 +93,12 @@ namespace osu.Game.Rulesets
                                 $"Ruleset API version is too old (was {instance.RulesetAPIVersionSupported}, expected {Ruleset.CURRENT_RULESET_API_VERSION})");
                         }
 
+                        if (r.OnlineID != instanceInfo.OnlineID)
+                            throw new InvalidOperationException($@"Online ID mismatch for ruleset {r.ShortName}: database has {r.OnlineID}, constructed instance has {instanceInfo.OnlineID}");
+
+                        if (r.OnlineID > 0 && rulesets.Any(otherRuleset => otherRuleset.ShortName != r.ShortName && otherRuleset.OnlineID == r.OnlineID))
+                            throw new InvalidOperationException($@"Ruleset {r.ShortName} shares online ID {r.OnlineID} with another ruleset");
+
                         // If a ruleset isn't up-to-date with the API, it could cause a crash at an arbitrary point of execution.
                         // To eagerly handle cases of missing implementations, enumerate all types here and mark as non-available on throw.
                         resolvedType.Assembly.GetTypes();