CVE-2023-36464: improved ExtractText(3) by pubpub-zz · Pull Request #969 · py-pdf/pypdf

@MartinThoma
my problems are this section of code

@pytest.mark.parametrize(
    ("dat", "pos", "expected", "expected_pos"),
    [
        (b"abc", 1, b"a", 0),
        (b"abc", 2, b"ab", 0),
        (b"abc", 3, b"abc", 0),
        (b"abc\n", 3, b"abc", 0),
        (b"abc\n", 4, b"", 3),
        (b"abc\n\r", 4, b"", 3),
        (b"abc\nd", 5, b"d", 3),
        # Skip over multiple CR/LF bytes
        (b"abc\n\r\ndef", 9, b"def", 3),
        # Include a block full of newlines...
        (
            b"abc" + b"\n" * (2 * io.DEFAULT_BUFFER_SIZE) + b"d",
            2 * io.DEFAULT_BUFFER_SIZE + 4,
            b"d",
            3,
        ),
        # Include a block full of non-newline characters
        (
            b"abc\n" + b"d" * (2 * io.DEFAULT_BUFFER_SIZE),
            2 * io.DEFAULT_BUFFER_SIZE + 4,
            b"d" * (2 * io.DEFAULT_BUFFER_SIZE),
            3,
        ),
        # Both
        (
            b"abcxyz"
            + b"\n" * (2 * io.DEFAULT_BUFFER_SIZE)
            + b"d" * (2 * io.DEFAULT_BUFFER_SIZE),
            4 * io.DEFAULT_BUFFER_SIZE + 6,
            b"d" * (2 * io.DEFAULT_BUFFER_SIZE),
            6,
        ),
    ],
)
def test_read_previous_line(dat, pos, expected, expected_pos):
    s = io.BytesIO(dat)
    s.seek(pos)
    assert read_previous_line(s) == expected
    assert s.tell() == expected_pos