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Disallow zero-length sliders from specifying a non-zero number of repeats (#35220)

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Bartłomiej Dach
2025-10-08 09:01:04 +02:00
committed by GitHub
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parent a08f7327b1
commit 1a522a19f1
1 changed files with 19 additions and 1 deletions
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osu.Game/Rulesets/Objects/Legacy/ConvertHitObjectParser.cs
+19 -1
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@@ -476,12 +476,30 @@ namespace osu.Game.Rulesets.Objects.Legacy
private ConvertHitObject createSlider(Vector2 position, bool newCombo, int comboOffset, PathControlPoint[] controlPoints, double? length, int repeatCount,
IList<IList<HitSampleInfo>> nodeSamples)
{
var path = new SliderPath(controlPoints, length);
// there are known instances of beatmaps (https://osu.ppy.sh/beatmapsets/594828#osu/1258033) which contain zero-length sliders with non-zero numbers of repeats.
// this was exploiting a bug in stable in which the slider repeats would be generated as objects but never actually judged as a hit *or* miss during gameplay,
// therefore increasing the theoretical possible max combo to be gained from a slider while in practice never giving that extra combo.
// due to lazer ensuring that an object has its nested part fully judged, this would result in broken behaviours
// (either the zero-length slider giving hundreds of combo for nothing if the repeats are judged as hit, or insta-failing the player due to HP if judged as miss).
// to remedy this in a way that seems least damaging, detect this situation via a heuristic and reset the number of repeats to zero.
// this technically *does not* match stable beatmap parsing or conversion, *does not* match in-gameplay behaviour of such broken sliders,
// and *will* fail conversion mapping tests, but again, this is supposed to be a least-worst measure to prevent exploits.
// it is also applied centrally to all rulesets rather than in specific ruleset converters because this failure scenario
// translates across rulesets (osu! and catch are both affected).
if (Precision.AlmostEquals(path.Distance, 0))
{
repeatCount = 0;
nodeSamples = [nodeSamples[0], nodeSamples[^1]];
}
return lastObject = new ConvertSlider
{
Position = position,
NewCombo = firstObject || lastObject is ConvertSpinner || newCombo,
ComboOffset = newCombo ? comboOffset : 0,
Path = new SliderPath(controlPoints, length),
Path = path,
NodeSamples = nodeSamples,
RepeatCount = repeatCount
};