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[skrifa] tthint: fix overflow in flip region instruction #1284

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merged 2 commits into from
Dec 10, 2024
Merged

[skrifa] tthint: fix overflow in flip region instruction #1284

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d196410
[skrifa] tthint: fix overflow in flip region instruction
dfrg Dec 10, 2024
f9601ed
fix it
dfrg Dec 10, 2024
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19 changes: 17 additions & 2 deletions skrifa/src/outline/glyf/hint/engine/outline.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -833,10 +833,13 @@ impl Engine<'_> {

/// Helper for FLIPRGON and FLIPRGOFF.
fn set_on_curve_for_range(&mut self, on: bool) -> OpResult {
let high_point = self.value_stack.pop_usize()?;
let low_point = self.value_stack.pop_usize()?;
// high_point is inclusive but Zone::set_on_curve takes an exclusive
// range
let high_point = self.value_stack.pop_usize()? + 1;
let low_point = self.value_stack.pop_usize()?;
let high_point = high_point
.checked_add(1)
.ok_or(HintErrorKind::InvalidPointIndex(high_point))?;
// In backward compatibility mode, don't flip points after IUP has
// been done.
if self.graphics.backward_compatibility
Expand Down Expand Up @@ -1385,6 +1388,18 @@ mod tests {
assert!(engine.graphics.did_iup_y);
}

// Add with overflow caught by fuzzer:
// https://issues.oss-fuzz.com/issues/377736138
#[test]
fn flip_region_avoid_overflow() {
let mut mock = MockEngine::new();
let mut engine = mock.engine();
engine.value_stack.push(1).unwrap();
engine.value_stack.push(-1).unwrap();
// Just don't panic
let _ = engine.set_on_curve_for_range(true);
}

fn set_test_vectors(engine: &mut Engine) {
let v = math::normalize14(100, 50);
engine.graphics.proj_vector = v;
Expand Down
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