`curveCurveIntersections()` segfaults with extreme finite coordinates

[marinelay]

Summary

curveCurveIntersections() terminates the interpreter when given two quadratic curves containing only finite floats with extreme magnitudes.

Versions

fontTools 4.63.0, CPython 3.12.3, Ubuntu 24.04 x86_64, glibc 2.39

Reproducer

from fontTools.misc.bezierTools import curveCurveIntersections

extent = 1e308

curveCurveIntersections(
    ((extent, -extent), (0.0, 0.0), (-extent, extent)),
    ((0.0, 0.0), (1.0, 1.0), (2.0, 0.0)),
)

Segmentation fault (core dumped)

ASan result

I built fontTools 4.63.0 from source with Clang 18 using -fsanitize=address,undefined -fno-omit-frame-pointer.
ASan reports a native stack overflow and shows the same generated Cython recursion frame repeated until the stack is exhausted:

ERROR: AddressSanitizer: stack-overflow
    #16 _curve_curve_intersections_t  Lib/fontTools/misc/bezierTools.c:25678
    #19 _curve_curve_intersections_t  Lib/fontTools/misc/bezierTools.c:26356
    #22 _curve_curve_intersections_t  Lib/fontTools/misc/bezierTools.c:26356
    #25 _curve_curve_intersections_t  Lib/fontTools/misc/bezierTools.c:26356
    ...
SUMMARY: AddressSanitizer: stack-overflow

---

I found this while fuzzing Python C extension modules.
I expected the function to raise a Python exception rather than terminate the process.