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[skrifa] tthint: overflow in move_index stack op #1286

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merged 1 commit into from
Dec 11, 2024
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[skrifa] tthint: overflow in move_index stack op #1286

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12 changes: 11 additions & 1 deletion skrifa/src/outline/glyf/hint/value_stack.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -193,10 +193,11 @@ impl<'a> ValueStack<'a> {
let top_ix = self.len.checked_sub(1).ok_or(ValueStackUnderflow)?;
let index = *self.values.get(top_ix).ok_or(ValueStackUnderflow)? as usize;
let element_ix = top_ix.checked_sub(index).ok_or(ValueStackUnderflow)?;
let new_top_ix = top_ix.checked_sub(1).ok_or(ValueStackUnderflow)?;
let value = self.values[element_ix];
self.values
.copy_within(element_ix + 1..self.len, element_ix);
self.values[top_ix - 1] = value;
self.values[new_top_ix] = value;
self.len -= 1;
Ok(())
}
Expand Down Expand Up @@ -346,4 +347,13 @@ mod tests {
stack.apply_binary(|a, b| Ok(a / b)).unwrap();
assert_eq!(stack.peek(), Some(0));
}

// Subtract with overflow when stack size is 1 and element index is 0
// https://oss-fuzz.com/testcase-detail/5765856825507840
#[test]
fn move_index_avoid_overflow() {
let mut stack = make_stack!(&mut [0]);
// Don't panic
let _ = stack.move_index();
}
}
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